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MG Midget and Sprite Technical - Thermostat help

My 1500 midget started over hearing today. Called the RAC and after a series of testing concluded that the thermostat had gone.

Removed the thermostat, added a new gasket so I could get home.

So bought a couple of new thermostats and gaskets. Spent some time this evening fitting one with a new gasket and it's overheating again! So took both thermostats and tested them in boling water, both ok.

RAC chap said the pump seems ok and think it is as I have driven it around without the thermostat in (30 miles).

So any ideas what it could be? Very confused!!
bk dyson

If the thermostat and the pump are fine, then to me it can only be 3 things:

1) An air lock somewhere in the system, it is rather easy to get one in a 1500.
2) A build up of crap in the cooling system, when was it last flushed?
3) A blockage somewhere causing part of the system to not get the cooling it requires

Not teaching you to suck eggs, but you haven't got a small leak somewhere?
R Williams

It was flushed last year, water does look quite rusty though. Would that account for it over heating when the thermostat is put in?
bk dyson

if it was flushed last year and now looks rusty....thats not good, I doulbt that rusty fluid acts a good heat transfer agent in the rad

Id say that needs fixing 1st... reflush, but use a good rad cleaner and turn on the heat so the water is flowing thur the heater maxtix...and use a good 50/50 green glyco mix

With the new fluid in, let the car run about 20 min. Without the cap on that will allow all the air out of the hidden recess of the inside of the engine,

Something you might consider that I do on all my thermo stats to avoid overheating damage from.faulty thermostates...I drill 1/8th inch hole in the stat face body, that way it can relive some of the the pressure build up

Another thought... how old are your hoses...are they collapsing in on them selves while the engine is running, If so need new hoses


But thats where id start, reflush with a good rad cleaner and heater on then fill 50/50 mix, leave rad cap off with engine running about 20 minutes to levitate the air out of the engine
Prop and the Blackhole Midget

when you flushed did you also back flush and remove the engine block drain plug and scrape the crud out of there?

you have advice from Prop and there's more advice in the Archives about refilling to avoid airlocks and hotspots, personally I've just followed the DH instructions and never had a problem (but I've not a 1275)

if you don't want to remove the rad and matrix (remember to open the heater valve) then -
• first clean the whole system with something like Bars Flush Cooling System Cleaner
• then drain the whole system - engine block, heater matrix and radiator
• use a piece of thick wire to clear out the crud that collects at the engine block drain hole whilst draining old coolant and flushing out
• flush each of the three until water runs out thoroughly clean
• reverse flush each of the three until water runs out thoroughly clean
• final flush through each of the three until water runs out thoroughly clean
• refill with the correct coolant mixture
• follow the refill instructions from the Driver’s Handbook or advice from Prop or more advice in the Archives

I used a Klingersil thermostat gasket and was very pleased with it
Nigel Atkins

Hi bk, believe them, its all in the clean out and how good that is. I have flushed, back flushed and re flushed mine after a near 10 year lay up and still found waterways blocked later when I took off the cyly head.

I am so bothered by it that even though I have had the head off twice for HG failure I have still flushed again since and have the flush for another go before the winter. Every time I flush more c**p comes out. Its finer particles each time but it still lodges in the bottom of the block waterways around where the drain is and I still have to poke the drain before the coolant will run free and drain out.

Mine no longer runs hot but it still has particles of rust in it that can be seen and that's after 2500 miles since back on the road.

I have the hole in the thermostat; it makes a big difference when refilling and topping up.

One flush in my opinion is just the beginning if you are over heating.

Having said all that the weather has been particularly difficult here this week and the last two days here have been cooler and mine has run cooler. 1500's are affected by the heat a lot and I am expecting all to be good on cooler days from now on. I will still be flushing though and in the long run am considering an electric fan with manual override for when it needs it.
Dave Squire (1500)

Brad,
just thought - check that the (radiator) pressure cap is the correct pressure rate for your car and carefully check it is in good condition, the seal and spring, as it is difficult to see if the cap has weakened renew it if in doubt

the scraping the crud out of the engine block on the draining of the existing coolant and on the two flushes helps no end

and if you can take the rad out and shake them as you flush and back flush even better

it also means you can straighten and gently brush clean both sides of the radiator fins

coolant is important as it also carries anti corrosive elements and these wear out before the antifreeze element so your antifreeze part could be up to standard but still best changed

if you wanted to extended the cleaning as well as the rad you could do the same to the heater matrix and replace as required seals,
Nigel Atkins

From BK Dyson's first post:

Did you test the (alleged) faulty thermostat once you got home?

Did the overheating suddenly occur, or was the engine temperature gradually deteriorating over several days/weeks?

When refilling the coolant, did you leave the screwed filler plug off for a few minutes whilst idling the engine, and slowly top up the coolant into the filler plug aperture? Did you leave the heater matrix 'tap' open?

I find it hard to believe that you have a waterway blockage problem if there is no overheating when running the engine without a thermostat. But I could be wrong.
Andy Hock

Andy,
I agree with you it's odd but you'd probably be surprised to see the size if some of the crud you can scrape out of the engine drain hole, some B owners think there isn't an aperture because it's blocked solid and work through with a drill bit

Brad(?) did put >>So bought a couple of new thermostats and gaskets. Spent some time this evening fitting one with a new gasket and it's overheating again! So took both thermostats and tested them in boling water, both ok.<<

I too wondered about the timing and build up of the overheating but it's overheating quickly now it seems

I did note rusty water water rather than coolant/antifreeze

can you put a thermostat in upside down :)
Nigel Atkins

*****Can you put a thermostat in upside down :)****

Come now gentleman, no need to be insultive

Just because I did it when I was 17 years old, 30 some years ago, dosnt mean everone does it ...hahaha

Prop
Prop and the Blackhole Midget

Its fairly unusual for a car to suddenly start overheating, unless there has been some other sudden "external" change causing it to overheat. So although advice on cleaning out the system, checking thermostat and filler cap seal is all good advice, these tend to give a progressively worsening problem, rather than a sudden change. I would be looking for some other fault, checking for leaks first. But I think you have done that.

I personally would then start with a compression test. If you don't have a compression tester ( they are pretty cheap and a useful item), then take it to a garage and get them to test the coolant for emission gasses, which will take minutes with the right equipment.
Guy W

Hi all

Thanks for the replies. I can confirm that the thermostats where all tested, the one that failed is broken and the new ones worked.

I am going to get the system fully flushed, all hoses are only a year or so old, rad is 2 years old and water pump works. I'm guessing that it's crud in the system, also that is mostly water in the system now not coolant as when I broke down water was just used. Timing is all good and regularly serviced so hoping its the crud through the system.
Keep you all posted!!
bk dyson

My experience is that just one bit of the system being bad can cause your problem.

Having said that all those new bits mean you have already 'cleared out' the system apart from the block and heater. Definitely take out the block drain plug and see if it drains out. If not get a cranked piece of wire (coat hanger wire is good) and push it in and around in there until a 'jet' of water comes out. The only way to properly clean the heater matrix is to take it out shake it about and back flush it.

However now I know about the new bits my suspicions are what Guy is thinking. Do you have any 'puttering' noises or a change of beat to the engine noise that you didn't have before? I agree with Guy; get a compression test done and I would do that first if I had a tester to hand to save unnecessary work.
Dave Squire (1500)

My two pennyworth...If a cooling issue it is generally progressive, unless one of your hoses develops a sudden aversion to containing fluid!

Thus, consider what is the root cause of the coolant system suddendly not being able to cope. Could be

Head gasket failure - a good indicator being bubbles in overflow bottle....usually

Vastly weaker mix caused by a bit of crud in the carb jet or a leak in a hose somewhere - check all carb hoses, spray in some carb cleaner or blow through jets - again indicators are usually a performance drop and and burnt plugs...

Fan still Ok I assume?

Oil level correct?

Consider also that any fiddling - on ignition timing say - done immediately beforehand could have had a knock on effect.

Mark O

Ok thanks

So given I have driven it around 30 miles without a thermostat are all these ideas valid? My point was that after fitting a new thermostat it didnt work
bk dyson

>>BKD wrote>> I have driven it around 30 miles without a thermostat

>>AH asks>>And what happened during those 30 miles? Did the engine temperature remain cool/cold? Did it get hot? What did the dashboard temp gauge read?

You have established that the original thermostat was faulty. My suspicion is that, when you are refilling the cooling system after fitting a new thermostat, you are creating an airlock which can cause overheating due to insufficient coolant flow. I repeat my earlier question: when you are refilling the coolant, are you leaving the screwed hex 'filling cap' (in the top of the thermostat housing) open and dribbling coolant in through that aperture? In my experience, that is the best way to eliminate air-locks.

(BTW, if you do have a damaged cylinder head and/or head gasket, one possible indicator is that your coolant hoses can become very hard due to the increased pressure of the coolant system/water.)
Andy Hock

Im agreeing with andy... air in the system

Leave the hex nut off for 20 minutes with the car idleing


You can also jack the front end up to shift the air bubbles

Prop
Prop and the Blackhole Midget

BKD

Thermostat operation is irrelevant to my points - so yes they are all valid. A working thermostat simply controls the point at which cooolant water is admitted to the block. It does not control anything thereafter. So if your engine warms up, then cools as coolant is admitted and you have checked the operation of the thermostat in the time honoured fashion of adding it to your mug of tea, or even fitted a new one, then it must be something else...

Driving around with no thermostat is fine - but of course engine will take more time to warm up from cold. How was it by the by? You need to check the coolant system for all points mentioned by others as if there is a fault there, as it is probabaly the easiest thing to establish. If everything is fine, then by all means have a look at other things - which may be the root cause of a perfectly functioning coolant system not being able to cope.

Mark
Mark O

BK,
whatever happens or the cause you want to thoroughly clean your coolant system and refill with coolant/antifreeze

if you premix the coolant or buy premixed then provided the system is as as empty as possible you know that the right mix ratio will be in there plus any top up will be with the correct ratio too (I don't know if that needs to be 50% if you don't drive in the very coldest of winter but the Driver's Handbook will say)

as your coolant hose are one year old if they're rubber I'd be interested to know if there are any signs of crazing (they'd be nothing to do with your overheating)

for checking head gasket failure I agree with Guy a compression tester or checking coolant gases, you can buy kits for this to do yourself

apart from what other posters have put all I can think of is

. crud and/or air lock in system somewhere
. external blockage/restriction to radiator
. brakes binding
. fan belt loose

you do need to check that the radiator is filled and not just the expansion tank (could be a sign of HGF)

ETA: just thought of another partial blockage of your exhaust but I'd have thought you'd notice a difference in sound if that was the case
Nigel Atkins

BK wrote

****also that is mostly water in the system now not coolant as when I broke down water was just used. Timing is all good and regularly serviced so hoping its the crud through the system.*****

Well... with that nugget, it could well be that it just needs a new flush and refill with coolant

That certianly explains the rust in the coolent or should I say "water"

I know some racers use water only and im sure water only will work for getting from A to B In an.emergency...but id think water only would loose alot of its effecancy

Because there is no luberication of the water pump, it could well be the pump is worn out if not already on its last leg to failure...spinning parts need luberication and water is not a good lubericant

With the hotter temps you guys have and the lack off coolant efficantcy of transfering heat ...this could well be why your seeing over heating issues

Prop
Prop and the Blackhole Midget

Hi all

I have now replaced the thermostat, flushed the system and added new coolant. All seems well. Used the tip of letting the engine run for 20 mins with the filler cap off. So guessing it was an air block?!

One thing to note, I could to locate the drain plug off the main engine block. I have a 79 1500, have I gone mad?
bk dyson

One of my first 'break down' experiences that I had with my '76 1500 was in 1979(ish) - an overheating engine in the area called Shepherd's Bush, west London. Not something that I would want to happen today. That was my hard way of learning that leaving the 'filler hex screwed plug' off whilst dribbling coolant into the hole and leaving the engine to idle for 10 minutes is the best way to fill a 1500 Midget cooling system - despite what any of the manuals say.

Re. main engine block 'coolant drain plug'. I believe that all 1500 Triumph engines have one. It can be found on the engine block, under the 1500 Midget carbs - the 'plug' is a flat-faced hex bolt, difficult/impossible to see when looking down into the engine bay. And even more impossible to access when looking upwards (from viewing when lying under the car). A real 'bar steward' of a position when draining the block.

Andy Hock

That's where it is and only do able touchy feelies so make sure the engine is cold for definite. Its this drain that is at the lowest point in the block so all sediment collects here and you may need to do some poking out with strong wire. (I used coat hanger wire cut to about 3" bent at the end as a 'wider' bodger). I found mine was absolutely full of rust and took three flushes (between drives) to get anywhere near cleared out even with flusher added.
Dave Squire (1500)

PS engine runs a lot better and cooler with crud out.
Dave Squire (1500)

Ah no wonder I couldn't find it! Is it easy to undo whilst "feeling for it"?

Looks as though I will be draining that and reflushing again this weekend
bk dyson

Brad,
with the plug is also a fibre washer so either have a spare or don't damage or loose the existing one

if the plug is anything like the same as on the 1275 then it's just a fraction of a turn to loosen or fully tighten but getting your spanner in the correct position for either can be fun - Dave would know the size (IIRC 11/16" on 1275) and whether ring or open ended is best to use

if you really need to you could try saving some of the existing coolant or just look at it as a flushing agent and dispose of the lot

personally I'd flush/back flush/flush the heater matrix, engine and rad again - if the rad and matrix are clean you'll soon see that on the final flush but I'd be very thorough with the engine and scrape as the existing coolant drains out and on the flushes and I'd repeat the flush & scrape/back flush/flush & scrape as Dave will tell you (and I found) the amount of crud you can still get out even after previous attempts is surprising

you know the slow fill and expel air procedure that suits you now and if you premixed the coolant before you might have some left to use, good thing with the coolant system unlike the oil is that if you overfill it'll just throw it on the ground and find its own level

also as Mark pointed out the oil is the secondary engine cooling system so keep the oil level well above Min and regular thorough oil and filter changes (get oil as hot as possible and leave to drain as long as possible to get as much muck and existing oil out as possible)

good luck let us know how you and the car get on
Nigel Atkins

Hey BK,

Id wait to flush, give it a few weeks and if the coolant looks rusty then flush ....if its still green and clean looking ...then id say your good to go

You have to remember, you where running straight water with no coolant, and that. A big recipe for rust inside these engines

If your just itching to fiddle, dont worry, im sure something will show up soon that needs atten.

Prop

Prop and the Blackhole Midget

Prop,
Brad wants to scrape the drain hole of crud so will be emptying out the existing coolant anyway

I think getting the coolant system in good condition is a priority on the engine

it's one of the first things I consider when I get a car new to me after the safety bits (and possibly a new battery)
Nigel Atkins

This thread was discussed between 26/07/2013 and 06/08/2013

MG Midget and Sprite Technical index

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