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MG Midget and Sprite Technical - Coolant Issue (again)

Evening all, I've been trying to fathom out why my late 1275 has been running hot again, and would like to get your opinions based on what I've deduced so far... Sorry, this is long, but I thought I'd give you as much info as possible up front.

Whilst the car was having various jobs done inc. a head gasket, it had a coolant flush (though not sure how thorough) and refilled with long life coolant, the orange stuff. Since then the car has been running hotter than I'd like, but usually dropped back to 80/85 when not under load and in decent airflow. However, with the hotter weather we've been having, I noticed that there was a lot of black gunge/rubbish accumulating around the rad' filler neck, so I asked the garage to drain/flush/refill, this time with std green/blue coolant, as I'd read that this was safer for older engines. This was last Saturday. They disconnected the lower hose at the tube, and also the upper heater hose / outlet at the heater, and flushed through with hose. What they didn't do, from memory was reverse flush, or bleed the system afterwards, though he did run the car up without the rad cap & exp' bottle cap on, does that count as a sufficient bleed?

On the way back, it was a hot day - 25+ deg c and up a steepish hill, the temp needle went briefly up to the 105-110 mark, and spent most of the journey at or around the 90-100 mark, so I tried to keep the revs down as much as possible.

Bit peeved when I got home so just stuck it in the garage and what with work/family etc, forgot about it for a while. Went in the garage again yesterday, to find a huge pool of coolant on the floor, though surprisingly, not the green stuff that had been put in, but the old orange stuff...!!! Anyway, on checking the rad' level, it was all good, about 2" below neck, which corresponds to the height of the expansion tank outlet on the other side of the rad. But the exp' bottle was at least 2/3 full, so I removed all the coolant from the bottle and measured about 870ml, way above the 500 odd ml it should contain, i.e. around half full.

Now, with the correct amount of fluid back in, I ran her up, and strangely the top hose seemed to start getting hot very quickly, around the 60 deg mark, as if the stat was already open or opened very early, and the thermostat housing seemed even hotter than the top hose. The hottest hose, however, was the lower hose that runs from the horizontal tube below the rad to the water pump, and was at its hottest nearest the pump / bypass pipe. The two heater hoses were also scalding hot, but the rad itself and the lower hose outlet from the rad were cool to the touch. I put it away for the night, scratching my head, and looked at it again this morning. More coolant puddles on the floor, but no really obvious signs of where it was coming from.

With the front up in the air i had a look underneath, and coolant was dripping off the leading edge of the front cross member, almost directly under the water pump housing, but the area around the expansion bottle overflow looked dry...

There was also a lot of oil, everywhere, which obviously goes hand in hand with the regular pools I find on the garage floor under the sump, now mixed with anti-freeze! I've been advised by the garage that it is the rear main seal, but it never leaked a drop before going in to them... To say I'm a little disappointed by the whole experience is putting it very mildly!

So, based on all the above (sorry its so long), what is the most likely cause of my woes? Air lock? Dead stat? Dead water pump? All of these? Another HGF (please... no...)? Car runs well, no obvious misfire, good power, no mayo under rocker cover, no sign of exhaust gasses in coolant (based on HC sniff test).

I've spent more time (trying) to get this car fixed, or worrying about the problems, than I have driving it, and have already postponed a trip to France in it, as I no longer trust the vehicle to get me where I want to go. All help / thoughts greatly appreciated.
M Weller

A couple of things spring to mind...

1. Water pump not pumping, for some reason.

2. Blocked, or partially blocked radiator.

You may also find that the thermostat was removed to try and cure an overheating problem - unless you know it is in there.

do you know why the head gasket failed originally?
Dave O'Neill 2

First thing that occurs from your description:
<<They disconnected the lower hose at the tube, and also the upper heater hose / outlet at the heater, and flushed through with hose. What they didn't do, from memory was reverse flush,>>

If that is all they did then they haven't cleared or flushed the engine block at at all. At best they have flushed out the radiator core and adjoining pipes. On the 1275 there is a removable blanking plug or sometimes a drain tap in the block, situated below the carbs. If it hasn't been cleaned out for some while, then the cylinder water jackets could well be choked which alone would cause the engine to run hot.

This might also explain how there was still some of the orange coloured coolant in the system when it had supposedly been fully flushed through!

Secondly, If checking the rad, then it should be brim full, not 2" below the top. Its a sealed system, with an expansion tank. If properly filled and the air bled out then as the system heats up the expanding fluid transfers to the expansion tank. And then as it cools again when parked up the coolant contracts, sucking back from the expansion tank to keep the system full.

A couple of cycles of this heating and cooling will fully bleed any air out of the system, although there are ways of manipulating things to speed up the process

Is the garage you are using experienced with midget or other A series engines?

Thanks for your thoughts.

So, check water pump - whats the best way to confirm if a water pump is working without removing it?

Remove stat housing and see if anything in there, if there is, pop it in some water on the hob with a thermometer and heat...

Flush and reverse flush rad...

Re the original HGF, no not conclusively, though the garage did mention that the head studs weren't as tight as they should have been.

Guy, no they didn't flush the block, either on its original visit or on Saturday. Is it the 12/14mm ish (imp') hex on the left side of the block, just above the sump & just behind the rear of the inlet manifold? Is it easy to flush this yourself at home?

I've never been able to get the rad level any higher than that, as soon as you try it just escapes out the expansion bottle outlet, which is the same height below the top of he rad on the other side.
M Weller

Yes, that's the drain point for the block. If its not been off for a while it could be tight to undo. My guess is that if you remove the hex you may find quite a lot of crud and rust behind which you can poke free with a screwdriver and then flush it as much as possible with a hose. Nigel might offer to send you his detailed notes on effective engine flushing - very thorough!

To fully fill the rad you should first fill the expansion tank 1/2 to 3/4 full, then put the expansion tank cap on. This will stop coolant simply running through as you then top up the rad. ( I understand that your rad has a filler plug - some don't) You can if you want (not essential) bleed air out of the highest point in the system which is the upper heater core connection.

Once you have done this it should have no air in, or any that it does have will be expelled as the system heats up and then be replaced with coolant drawn back from the expansion tank as it cools again. Squeezing the bottom hose a few times may help to expel air as well.

Just make sure that you check and top up the expansion tank after a couple of cycles and don't allow it to get too low.

I am not addressing the other issues with thermostat or water pump as you have the advice on that.

ETA: I appear now to be a couple of posts behind but this post still stands whilst I catch up.

I'm with Guy they only flushed the rad and top and bottom hoses and only partially at that.

Very important to clean out the engine block drain hole if you don't know if it's been done.

They could have bleed the system using their method. Following the very simple refill instructions in the Driver's Handbook has always successfully bleed the system for me but as Guy has put there are some simple other methods should you still have problems or not followed the DH instructions.

There could be a partial of full blockage as Dave suggests.

If the coolant was just orange does that mean that none of the green was mixed with it then?

I think your expansion bottle back filling is a sign of of the overheating. Does the expansion bottle hose go below the chassis, if not it could be that which is making the front crossmember wet even if it doesn't show on the end of the overflow hose as it'd be coming out hot. Whether it does or not you could direct it, or oversleeve it to a container to see if coolant comes out of it and how much.

What you need to do whilst you have the car in the air is to run it up to temperature then turn it off and see where it leaks or overflows and what colour coolant.

I'm not sure the orange stuff was a good idea nor and mixing it with the green stuff so I'd clean, flush/back-flush the WHOLE heating system getting all the existing coolant out and completely refilling with traditional.

Getting all the coolant out takes a bit of effort but it's not difficult, too time consuming for a garage perhaps.

I think I sent you my thorough but very simple method, I'd suggest you do the work yourself rather than pay twice for a short job. Do at least the more basic method I describe, it's very easy and you'll be able to tell as you go along and do one piece at a time if or where there's any blockage.

Nigel Atkins

Will flush/back flush whole system again, as per your notes Nigel. Don't think the coolant pooling on the front cross member is from the exp' bottle overflow, as puddle from last nights run-up was without driving the car, just starting / ticking over in driveway, so no airflow to blow coolant back from overflow to cross member.

Yes, no sign of the green coolant in the first slick... all orange, well orange tinged... very strange!

If you bleed via the upper heater hose / outlet, do you remove jub' clip at heater end or at the solid tube end by the inlet manifold?
M Weller

The engine block drain plug is item '2' in 'Fig 1'.

I think it's something like 11/16" spanner, it's a bit awkward to get at but the initial loosening and final tightening is very little movement of the spanner if there's a washer fitted.

As always with fittings that haven't been removed for a while first clean around them and scrape off any crud/muck/rust seal you can see then a good dose of PlusGas (not WD40) and leave for a while whilst you do over stuff or have a mug of tea. Then try to tighten a little first, if you can, to break any crud/muck/rust before loosening, if no joy repeat PlusGas and leaving a while.

Refill/bleed instructions are also below.

ETA: isn't your system as below (minus item '3' perhaps)?

Nigel Atkins

I'm not sure if the notes I sent you included the following with more detail on flushing and getting more of the existing coolant out -

Flushing and back-flushing

Iíve found just using an ordinary ĹĒ (15mm) open ended plastic garden hose is ideal for fitting to the heater matrix inlet and outlet, an off cut of the same hose is ideal to use as an outlet for flush water going into a bucket, that way you can see and inspect the crud and muck that comes out and also capture the waste water.

You can easily and quickly reverse the position of the hoses on the matrix inlet and outlet for back-flushing and you donít need to secure the hoses with clips unless you have particularly high pressure cold water mains, if so also donít turn the tap on too far, you want to clean not damage.

If you are particularly worried about electrics getting wet then cover them in cling film (I only bother to do this if Iím cleaning the engine bay and will be fully rinsing the engine bay).

For the radiator you might want to use some sort of adaptors or just rags around the garden hoses if the radiator is remaining in the car.

For the engine again depending on where you use as access and drainage points you might want to use some sort of adaptors or just rags around the garden hoses as hose seals.

On each drain and each flush I like to syphon or blow out the residue liquid from the matrix, engine and radiator as a very surprising amount of liquid is left in despite your best efforts to drain Ė I had the radiator out of the car and shook it every way yet there was still some liquid left in it.

I blew the water out by just using the drain off-cut of garden hose and my lungs Ė but donít overdo it as you could hyperventilate.

For syphoning I used a very simple plastic syphon bought off ebay (you can get then for around £4 onwards) which Iíve used for various jobs on the car over the past few years so well worth the investment.

After a thorough clean like this if you use the correct coolant mixture and regularly change this coolant when required (usually every 2 years) then future changes should be just drain and refill.
Nigel Atkins

One way to check water pump operation is to remove the top hose from the radiator and direct it into a bucket, then start the engine.
I think the 'stat would need to be open first.
Dave O'Neill 2

I've just noticed something I missed on the extra notes - make sure, especially in your case, you empty out the bottom metal cross pipe as a lot of liquid can sit in there. Easiest way is to syphon out with both ends open, rubber hoses removed, then a final blow out for the last bit.
Nigel Atkins

Finally from me (well for tonight) :) - you did say you have a copy of this book?

Nigel Atkins

Some useful points there to help me along the way, thanks. I do have a handbook, and can confirm that I don't have a drain in the rad cross tube - no.3, and no.2 is what I suspected it was. Tell me, they say to do the drain on level ground - is there any reason you couldn't do it nose up? I'm thinking of the block drain plug here?

I'll try the top hose trick too before draining the whole system to check the pump.

Do I replace the block plug as a matter of course, or just the copper washer, if fitted?
M Weller

Oh, I meant to ask, when stationary at idle, how hot are the cooling fins / inner face of the rad supposed to get? Only my top hose gets pretty hot very quickly, as does the hose from the cross pipe to the pump, but the rad face itself is only very slightly warm and the little lower rad outlet hose always feels cold.
M Weller

sounds to me like a slightly blocked rad.
you mention the top hose getting hot quickly, and from how I read it only a partially successful flush through.
I would whip the rad out, and get that pressure tested/ looked at by a specialist.
P Bentley

I think its the water pump, plus maybe clogged block waterways.
If the pump isn't working then it won't be pulling water through the rad tubes as it should. The top hose will still heat up quickly as the water rises thermically to the top and this will also make the thermostat open quickly. But with a piss poor pump performance it wont then circulate through the rad, leaving the fins and bottom hoses cold.

My concern is the huge pool of coolant on the garage floor if it didn't come from the expansion bottle overflow, could there be a leak from around the water pump(?).

I can't think of the diagram of the engine water ways so can't think where the coolant will get trapped but just to clean and drain the engine block drain hole you could do it nose up but to get all the coolant out which is what would be best to do you'll have to have the car level I think.

On a usual coolant change a lot of the existing coolant is left in the system which becomes obvious when you measure how much you use to refill, if the system was completely empty then it should take 6 pints (3.4 litres) including heater, as per DH.

As for the engine block drain plug it doesn't need replacing unless the sides have been rounded and the washer can be reused (unless it's the squashed type then I'm not sure). The washer is the same washer as the sump plug washer.

The reason I checked if you had a copy of the DH was that the refill method in it, along with other very useful info, I've always followed and had no problems.

A poor water pump might be a cause or contributing cause of the problem but I can think of a wild card blockage along with the usual blockages or partial blockages.

When you flush the rad you should be able to tell how blocked up or otherwise it is.

If you have to completely remove the radiator and replace the water pump it's not a difficult job even I've done them (rad out several times) and one advantage is that you can clean even more and better the coolant/heating system and you can easily get to do a couple of other small jobs at the same time if required.
Nigel Atkins

further thought. . .I wonder if it is possible that there is a break in the impeller shaft. So the outside is turning via the fanbelt drive but the inner is not.
With the coolant being stationary then it would get hotter at the top in relation to the bottom of the Rad.
Either way, I would still remove the rad for a cautionary check which makes changing inspecting the water pump and bypass hose easier still.
Go to it Mr Weller and report back !!
P Bentley

I had a problem just like that. I had serious overheating on the way home from a track day at Silverstone leading to a serious engine failure on the M6. I thought the cause was HGF so expected the overheating to be gone after I rebuilt the engine. Actually the HGF was a symptom not the cause and the overheating continued. I tried everything I could think of and even had the radiator rebuilt with more cores but it still over heated. Until I removed the plug on the lower nearside of the engine block (as described by comments above) and left a hose to flush out the block for half an hour or so until the water came out clean. I've had no problems since (except the engine runs a bit on the cold side now).

The odd thing was that I had no overheating problems for the hundreds of miles before or during the track day. I happened very suddenly so I'm guessing that a lump of 'crud' must have shifted inside the waterways and blocked something until my final flushing exercise.
Chris Hasluck

I'm guessing that removing the engine block drain plug (or opening the tap on earlier cars) is almost always overlooked or ignored on drain downs, cleaning and coolant changes.

Those like Chris, me and a few others on here who have seen how much crud can come out when the drain hole is opened and cleared know how important it is.

My engine was reconditioned but when I done the first coolant change at 2,000 miles from recon I was surprised how much crud came out of that drain hole and even at the next (distress) change 11 months and 5,000 miles later there was still a small amount of fine crud left to come out.

And anyway, who are we to go against the word of the good book!

"A drain plug (2) is provided on the engine cylinder block."
Nigel Atkins

Cool running from high quality cleaning is where it is. After the crud came out of mine and the sludge out of the heater, radiator and header. And I cleaned the hoses (still mainly original) it ran so cold Nigel gave me a high temp thermostat to keep tootsies warm in the winter. (Still many thanks Nigel). It's still in there in the warm weather and going fine 3 years or so later.
Dave Squire

I realise that I've got to go the whole hog and do rad, block and heater, all pipes etc. Tell me, are there any tips for removing the rad? I have the process in theory in the Haynes manual, but new(ish) parts and 43 yr old parts rarely come apart in the same manner...!!! So, any time/knuckle saving tips/techniques would be appreciated. I've never removed a rad in my life... sad I know, but...

I've been soaking the block drain plug for the last couple of days, and have a syphon on order. Just girding my loins now and waiting for parts.

I'm afraid I'm at the stage where I don't trust anybody, specialist or otherwise, to do a job properly anymore. So, I don't have a choice but to start learning more about the greasy side of things. I actually enjoy it once I get started, just always worry that I'm going to bu**er it up in some way...

Thanks everybody for your assistance thus far, lets hope my outcome is similar to Chris's & Dave's...
M Weller

No problem Dave. I must admit I just couldn't get used to seeing the needle near and after the 'N'. In the depths of winter sometimes it'd be nice to see the needle nearer the 'N' but even so the heat in the footwell is very warm and more often, even in winter, too hot.
Nigel Atkins

There's nothing difficult, sometimes the odd screw, nut, bolt, fixing might be awkward to undo or get back in so just take your time.

Take plenty of photos from all angles or drawings.

Note which way jubilee clips and fittings face as you remove them, whether they are easy to get at or not so when you put them back you can still easily get at them with everything back in place and more awkward to get at. What I mean is putting a clip or fixing back on in a certain position/orientation when the rad and shroud are out might be easy to get at once the rad and shroud are back in.

Pick a time when you won't be in a rush and have access to shops, allow loads more time than you think that way if you finish early it's a bonus. Personally I'd pick when the weather is warm as you wont mind getting wet so much.

Soak all fixings with PlusGas as long in advance as possible, have all the correct sizes tools and new spare fitting to replace any worn ones. Coppergrease.

You can do the job by yourself but a second pair of hands might be useful if, like mine, the shroud sliding locating bars don't all want to slide.

Once the rad is out you'd be amazed how difficult it is to get every last drop of whatever liquid out even if you shake and tip it every which way and lay it on black plastic bags in blazing sun.

Start by cleaning, draining, flushing and back-flushing as much as required, then final draining - removing all hoses, syphoning/blowing out as required.

Remove rad grille, remove rad and shroud, inspect water pump and gasket, bypass hose, fan belt, etc. etc..

Refitting the outer screws and nuts at the top of the rad grille is the most difficult bit for me so I get my wife to literally give me a hand and thinner fingers.

I can't remember what I've forgot but I will be replacing my rad this summer sometime when I can be bothered so if you find any difficulties let me know so I can be reminded or prepared, thanks.

Nigel Atkins

It is a long time since I have taken a 1275 rad out. Am I right in thinking that when putting it back, it is easiest to put the short elbow on the bottom of the rad first, then feed it onto the cross tube as you refit the rad?

Also, if there is a chance the rad might have some mayonnaise inside (you mentioned changing a head gasket), then I found the rad would just fit in a domestic oven; warm at a low temperature and it helps to turn the mayo back into liquid that can be poured/shaken/flushed out.

If you get stuck with anything, at least you have this forum to help (I don't think it was available last time I had a 1275 rad out!).

Jonathan Severn

For the difficult bottom hose on a crossflow I changed to a Samco silicon one - difference in flexibility/easy of fitting was well worth the additional cost.

Also most new rubber hoses are rubbish anyhow !

richard b

The small rubber bottom hose is a bit fiddly, possibly it's swings and roundabouts for loosely fitting it to the rad first if Sod's Law comes into play and it catches or folds on end edge of metal cross pipe but overall that sounds a thing to try.

I can't remember if I've tried that but have had silicone hoses for a good while anyway so as Richard says more flexible..

That small bottom hose certainly doesn't want to be too short but sometimes it can be just a little too long and make fitting just a little (more?) fiddly.
Nigel Atkins

Jubilee clips - something I've not put, if any of the clips look slightly suspicious then use new instead, I've had one of the large ones that has slightly ovalled so when you think it's fully tight it's just that it's stuck. When checking tightness, say after you've fully warmed the engine and after the first run and the engine has fully cooled down, then you want to slightly loosen the clip before tightening to check it's not just stuck rather than tight.
Nigel Atkins

ETA: by it's first run I meant first road run
Nigel Atkins

Cheers for the tips guys. Wondering whether I should have ordered a pump too... or just wait till its all apart and order then if required?

Oh, and is it easier to undo the block drain plug from above or below with it up on ramps?

And, is it safe to run the engine briefly without coolant to get it back in the garage overnight?
M Weller

I checked in March this year MGOC pumps are still good and only cost £15 (check year for vane depth). I changed mine as a matter of course only to find the one already fitted was obviously new when I looked at the insides.

I don't think you need the car on ramps unless it's very low. I'm not sure if you can get at the plug from below but it's a bit tight from above if you have twin carb heat shield but can be done, watch your knuckles on initial release.

If the car is on ramps you'll probably need to be taller than me (5' 6") or stand on something solid to raise you.

Oil would be the coolant if there's no water coolant but the water coolant also lubricates and cools parts the oil doesn't get near enough to - the water pump's not going to be happy without water for a start, then I suppose if there's some residual coolant in some parts of the system perhaps the air in the missing parts might cause problems - I'd say push it in the garage, or filling it full of just water will be fine for this purpose - or do the work outside in the sunshine (lie those of us without a garage). :)
Nigel Atkins

Yes, safe to run the engine briefly with no coolant.

If putting the rad in the oven, make sure the other half is out!
Dave O'Neill 2

I was too much of a coward to suggest doing it, I'd worry about what briefly means, that it's someone else's car not mine, that Sod's Law strikes.

Coolant overheating is another good reason to have the wider safety margin given by better quality oils in the engine and gearbox at least, every little extra margin adds up when things start to get hot.

Not that I'm suggesting a brief run to get in the garage will get things that hot.
Nigel Atkins

When I say ramps I mean the little drive on variety!!!

And I will be doing the work outside, you wouldn't be able to do much in my garage, except perhaps polish the front and rear number plates...

There's a steep ramp up into the garage too, had some fairly interesting 'pushes' up the ramp in the past when no one around to lend a hand!
M Weller

Funny that I was just about to post, whilst doing the washing up I thought if you have ramps you could add a couple of axles stands at the rear to lift the car and have it level.

I've got two small ramps, well 4" blocks of angled wood but I really need four - do you use your steep garage ramp at the rear and small ramps at the front to lift the car and keep it level (handbrake, in gear, chocks etc.).

I regularly clean and polish my front and rear reflective numberplates (and lights), more regularly than I clean the car so that I can be seen at night, it also makes the car look cleaner when it isn't, soon get dirty anyway without a garage.

My days of pushing any car are now over and it was a couple of decades back that I found the level road I live on actually has a slight rise that I hadn't notice before.

A couple of years back I actually hurt myself pushing a modern Porsche because the battery was flat as the owner was in dispute with Porsche because you have to buy the expensive battery from them and the car wasn't that old, he could have turned up in his Westfield which would have been easy to push start, but he didn't. This was at Gaydon motor museum and they lent him a jump starter that looked like something out of a 50s si-fi film, amazing looking bit of kit.
Nigel Atkins

Ive had water pumps leak when they go bad

Becuse yourgoing on a long trip Id probably change out the water pump and put in a new stat...both are cheap and easy to do

To drain off the air... i always jack the front of the car up high then add the fluid that way the air is forced out to the highest part

Then i run the car at idel about 20 minute with the cap off then set the car down level let it cool for a bit, then cap it and run agian for 15 minutes watch the gauges for over heating

1 Paper

I'm thinking you could be right re the water pump.

I checked by removing the top hose with engine running and there was coolant coming through, but not sure if it was at the correct rate, as I have nothing to compare it to. New coolant puddles under the car every day, very difficult to see exactly where its coming from, as there's so much gunge etc from the rear main leak... But it seems to be dripping down from the rear edge of the front cross member, so could very well be the pump, even though it appears to be working. Strangely, even two weeks after the last coolant change (to green standard coolant), the puddles are still the orange long life coolant that was drained out...!!!

I eventually got the block drain plug out, having tried to use a 3/8 W ring spanner with no success. Eventually got the bugger with an 18mm socket on a long 1/2" drive wrench. To my surprise, coolant immediately flowed out, with very little detritus either. Bit miffed as I'd secretly hoped that was going to be the cause of my overheating woes...

Flushed and back flushed the radiator too, very good flow out the bottom hose, again hardly any rubbish.

Now, here's my problem. I disconnected the heater top hose, the outlet, and attempted to flush the heater out by flushing through the top hose again. With the heater tap open I reasoned that the water would go to the rear of the block, through the open tap and round the heater and back out, but instead all the water flow came back out the block drain much lower down? Surely as the heater is higher I would have expected to see some flow from the the heater outlet? Or should I have put the block drain plug back in first?

M Weller

Water pump output I donít know so will leave to others.

Leak could be water pump or its gasket or perhaps rad, cross pipe, hoses Ė you could dry everything then wrap tissue round various areas to see where it soaks up the leak allowing for fact that the leak coolant can travel.

The fact that the leaks are orange concerns me as it might suggest a blockage or air lock as I thought youíd get some colour mixture between the two types of coolant but I could be wrong as I have a poor memory and donít have the two types to mix as an experiment.

Obviously 18mm will get the drain plug out as youíve done it but I wonder if it might round the edges a bit and 18mm is around 11/16Ē AF my memory was probably right about that.

Even though not much debris can out on the drain itís still worth the flush and back flush to make sure itís clear around there, especially if youíve not used a cleaner on the system before.

For the back flush of the rad it works better to have the rad out and upside down and even shaking it between flushes, I found it difficult to get all the residue liquid out each time so assume some crud might also be sitting in the residue liquid.

Top hose is inlet, heater tap hose goes to the top pipe connection Ė this is where photos of your engine bay would have been helpful, if your heater is plumbed other way road it would be noticed. Either way, disconnect the hoses and flush water through one with the other running to a bucket so that you can see what comes out and are able to dispose of it as required.

Flushing the rad and heater in situ is OK but a much better job can be done with them out of the car particularly the heater matrix as again it can be shaked to clean and empty out residue plus brush clean the fins and check the condition and position of body and interior seal.

For the block you could run water through the heater tap and another way through the block drain hole if you can get a hose to it, not easy and a reducer pipe or metal pipe with bend would be handy.

You can after that put the drain plug back in to flush out through other outlets / inlets.

There are my notes and additional update in a previous post on this thread, or just let me know - and/or keep posting here. Keep going you will get to the bottom of this coolant business.
Nigel Atkins

The orange coolant may well be from the expansion tank as that does not drain - empty with a large syringe etc - mine often has a rather nasty sludgey stuff in it even after cleaning !

Cleaning the heater matrix - i had to replace mine as it never flowed well even after cleaning.

As Nigel has said try identifying the leak location his tissue idea works well - cleaning down the engine helps.

If the pump is leaking you can usually see it when its hot and running or just after turning off when hot as the temps rise a bit.

From earlier posts noted water not drawn back into rad from expansion tank on cooling even with low rad level - air leak/pump leaking or blocked/colapsed coolant pipe to expansion tank/tank cap rusty/sealing issue ?

richard b

Thanks chaps, more things to investigate in due course!

Re the heater hoses, the inlet (via tap) is definitely the lower hose - if that's wrong way round, could that be causing a problem?

M Weller

Not a great pic, but you get the idea, yellow hose is connected to outlet, but nowt came out when i shoved the hose into the top hose, as I said.

And you certainly couldn't eat your dinner off my engine bay I'm afraid... sorry!

M Weller

Thanks I'll try that. Does it matter which way the water from the tap goes in - inlet or outlet?
M Weller

Sorry totally my mistake, I had another brain fart, your heater pipes are correct way round.

At the risk of me looking stupid again - the heater tap looks closed(?) but it might just be angle of photo(?).

Easy way to test if the heater matrix is blocked is to put a second open hose on the bottom connector to a bucket and turn on water.

ETA: no the matrix wouldn't be your problem anyway and don't worry about engine bay as most of us don't have show cars.
Nigel Atkins

Sorry got distracted - I'm not sure that it does matter that much but I could well be wrong.
Nigel Atkins

Have a look at the underside of the bonnet. Often if the water pump is leaking, coolant will be sprayed around by the fan, including the underside of the bonnet. Of course, if there is no coolant there, it doesn't mean that there is not a fault with the pump.

If you suspect that there is still some orange coolant in the expansion tank you could just take the cap off, insert the hose pipe and flush vigorously with clean water. That should get most of the orange out, though it will be a tad messy. Perhaps ask an assistant to watch the expansion tank closely while you turn the tap on and off from a safe distance...
Jonathan Severn

I've tried the hoses both ways round and can't remember noticing any difference but I don't remember much.
Nigel Atkins

Tap is fully open, well near enough I usually don't leave taps like this tightly open / shut if I'm leaving it for a while, normally just back off 1/16 of a turn.

I've already siphoned everything out the expansion tank, so I don't think the puddles are coming from there, only green coolant in there. Strange thing about the orange coolant on the floor is that it looks 'clean' - would love to know where the old girl is secreting it away...
M Weller

Good idea not to fully open so that it doesn't sieze but I've found with mine that if I don't fully close it the heater gets hot. I should check mine more often as it only gets opened or closed a few times a year, it remains open during cold winter and closed the rest of the year.

I must have swallowed a bucket load of silly pills today as after tea and washing up I went outside to lift the bonnet on mine to see the wheel on the tap sits very close to the body of the tap when it's closed, shows how much I notice, I could say I thought possibly you'd got the other type of tap with the longer spindle but I'd be lying, it was just the silly pills.

I did wonder about putting that the expansion bottle had been questioned before but I thought it'd come out sounding a bit patronising in my usual rush, which is why I wonder about the puddle being so orange, have you tried mixing the orange and green to see if they merge or remain separate?

If they do merge a bit then it perhaps suggests a leak and a blockage, even a blockage leading to a leak?

Another reason I'd suggest taking the cooling system apart a bit or at least checking all openings for blockage - crud or even something left in by mistake, bit of rag or paper that was supposed to temporarily cover an exposed opening and forgotten about when things where put back together (or is that a touch paranoid?).

(Could I have severe man-flu coming on?)
Nigel Atkins

Nigel, I think you're right about the very thorough approach, leave nothing to chance etc. I suppose I'm just always a little cautious about pulling loads of stuff off / apart, as by my own admission, I'm pretty green when it comes to dismantling/diagnosing/fixing old cars. I always wonder if it will ever go back together again properly!
M Weller

you'd struggle to open the bonnet if you were any worse than me and I've had the rad out at least twice (soon to be thrice) on my present Midget let alone the other bits of the cooling/heating system .

Do as I say and not as I do like sometimes relying on memory (like I did earlier in the thread) instead of checking and double checking (like I didn't do earlier in the thread).

As I've put before -
. allow loads of time (I'd allow 2 dry days and not worry at all about how quick others might be able to complete it, if you finish earlier great)
. have things prepared (parts, tools, etc.)
. don't be in a rush
. take loads of photos if you can at lots of stages before moving on
. try to do as much as you can when the shops are open in case you need something extra or run out
. if you need an extra hand get an extra hand even if it means taking a break
. check twice before you do anything ("measure twice to cut once" principle)
. be thorough - if you can be thorough fast great if not take your time, don't cut corners - do a good job once not a poor job two or three times, anything you skip or skimp Sod's Law you'll regret later
. don't assume what's on now and how it is is standard or even correct, check

It really is just a matter of undoing fixings, cleaning and reassembling, nothing difficult, perhaps the odd awkward bits where something won't line up or go on straight away and then out of the blue they fall into place for no really good reason.

I tend not use the repeated swear-words method now i take a break instead, have a mug of tea and a pee and when I return things seem to be easier, if not or I'm fed up/bored with it I leave it for the second day, if it is the second day I leave it for the next or another day. The car has to work for me not the other way round (bit like computers but a lot less frustrating).
Nigel Atkins

Anybody know where I can get a decent quality water pump? I can't believe the ones at Moss are any good for £16...

Wonder if they have a cast iron impeller or just stamped steel?
M Weller

Try Minispares or Leacy MG
Dave O'Neill 2

Thanks, Minispares do a slightly 'improved' version for a few quid more, looks about the best I can get.
M Weller

think mine had a plastic impeller, be surprised if it were metal given its propensity to rust
P Bentley

check with MGOC Spares if they still have the same pump as I bought a few years back the standard pump they sell at £15 was very good, made in Turkey or some country where they lost building ships or ship parts.

Also whilst I remember check your pressure cap for condition and that it's correct poundage, 15lb.

And something I've forgotten previously, grommets in the heater box face around the holes for the heater matrix inlet and outlet pipes, they help to hold the pipes when fitting and removing heater rubber hoses and help to seal the heater box just that little bit more.

MGB heater here but gives you the idea of grommets and seals that help to get the heat into the cabin.
Nigel Atkins

All the standard non oem ones are either stamped steel or cast iron for the 'better' ones. The 'Evo' pump from minispares has a 'glass filled plastic impeller'. Not sure which is best, but based on the descriptions, I'm going with the Evo version.
M Weller

Bit of overlap there Nigel, but yes I've checked pressure cap, its all good and the correct 15lb version. Will look into the heater pipe grommets too.
M Weller

you night have missed my last post.

And the grommets only help hold the pipes a bit didn't get time to edit that in.
Nigel Atkins

Double overlap now.

New fan belt?, check size.
Nigel Atkins

Is it worth changing it anyway while everything else is off (looks ok...)?
M Weller

Do you know if it's new(-ish)? is it a good make? is it correct size (if it comes off, goes on and adjust well then it's a good fit).

You can always replace it later but at £5 or £6 whilst everything is out of the way now's not a bad time.

If the rad is out and if required now is definitely the time to replace the bypass hose if needed as that can be a pig to fit when everything is in situ.

Personally I'd use either silicone hose or an off-cut of good quality thick walled hose so that it's fit and forget (bear in mind a lot of rubber can be piss-poor).

Hi-res (within board limit) photos of the state of play might help spot things (not the fan belt unless you have a lens that can zoom in that much).

I keep finding other small jobs that need doing when I change my rad and completely (well as much as possible) empty out the existing coolant that will probably mean too much time working on the car instead of driving it.
Nigel Atkins

Don't know how old it is but looks ok to the untrained eye! Will probably just get a new one, are there any better quality ones out there? Do Gates make them?

Re the bypass hose, if I go for the thick walled offcut option, is there anything I need to look for spec/material wise? Or just match up length & ID?
M Weller

Gates are good as far as I know, the last Gates I had was good too.

Just match up length and ID (1/2" IIRC). I got an off-cut from a local trade supplier for free (well I gave him enough for a vending can of Coke) that way I could check quality. I will replace it with a silicone cut piece sold (with clips) by some company in Wellingborough, I forget who now but I could look it up if you wanted.

I'd strongly suggest you take the existing bypass hose off first to check it was long enough to fit well and see how well the jubilee clips fit (very little space to grip on adapter under stat) and note the position of the screw heads so that you can still get at them when the rad and all the hoses are back in place (same for all the jubilee clips).
Nigel Atkins

This thread was discussed between 13/07/2017 and 01/08/2017

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