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MG MGB Technical - Radiator

I am the owner of a 1971 MG B and radiator cap is broken. It has an inscription of lbs 4. G 280 U2. but in the spare parts catalogue I just discover the 10 and 13 lbs. What must I do as replacement? I live in Portugal with temperatures from 10 to 40 Celsius.
ALFREDO SIMOES

Alfredo,
you would normally have a 10lb cap on a '71.

4lb caps go back to earlier cooling systems on other cars and not on a MGB as that was 7lb.

So it makes me wonder if it was just a mistake to fit 4lb on yours or if it was fitted by someone else for a reason.

Is the car new to you?

Does it have the standard radiator fitted?

A photo of the radiator also showing cap position on radiator or expansion bottle might be useful.
Nigel Atkins

There are short reach caps and long reach, so if you have a 4lb cap fitted now it may be because you have a non-standard radiator.

A 71 would originally have had a 'top fill' radiator with the filler cap centrally on top of the header tank, 67 and earlier had a rear fill where the cap was on a neck behind the radiator. But that doesn't seem to be the whole story for what size (not pressure) cap you need.

You need to measure the depth of the filler neck, from the inner sealing face to the top of the neck. These can be 19mm and 26mm, and there is some difference of opinion as to which was used when on the MGB. You also need to measure the cap from the main rubber seal to the upper spring seal, and these need to be a mm or so longer than the neck. The caps on both my 73 and 75 V8 are 20mm.
paulh4

Sorry for the delay in sending pictures. I have this car since 2001 and since then it is the same radiator but I suppose that it will not be the original.
Is it possible, with the photos to confirm it?


ALFREDO SIMOES

Another image


ALFREDO SIMOES

Thanks photos help.

I wouldn't know if the rad is original or is an original type for sure but it looks like it is to me.

Either like far too many B owners you do very (too) little annual mileage as it all looks very clean (externally, the cooling system internally might not be so clean), the alternator looks very clean is it unless it new(?).

If there are no other variances from the standard on your cooling system then the rad cap is rated below the usual (10lbs).

Do you mean your rad cap is 'broken' because it is letting coolant out now and didn't before?

Good idea to fill the gap between the rad and surround to help get the cooling air through the rad more.
Nigel Atkins

Here is the part you need Alfredo to fill the gap between the radiator and the diaphragm. It's a self adhesive foam seal and not too expensive.

https://www.moss-europe.co.uk/seal-diaphragm-to-radiator-foam-ahh8887.html?assoc=108511

Andy
Andy Robinson

Alfredo,
1. Your climate is not important.............just something to envy!!!
2 The cap determines the pressure within the system.
3. The pressure is necessary to stop the coolant boiling.
4. Measure the neck depth as Paul suggested.
5. Check that your new cap has the correct dimensions, i.e., slightly longer than the neck depth. I've bought one or two, supposedly "correct", which were too short, so the system didn't pressurise and i was losing coolant.
When you fit the correct one, you can feel that you are compressing the spring to engage the lugs.
6. Choose the correct pressure cap for your year, i.e., GHN 4 & 5, 10lb/sq"
Allan Reeling

Does look like the original style for that year.

I can recommend the foal seal between radiator and mounting panel, I was surprised how much effect it had in very warm weather even in the UK.

However the two sections parted the first time I drive the car as there was barely any adhesive between them. Fortunately the radiator section (which isn't glued to the radiator, only the panel section is glued to the panel) was still in the engine bay and with fresh adhesive it's been fine since.

Also fit the rubber seal along the top of the mounting panel, to seal to the bonnet.
paulh4

Sorry for my late reply to your comments but I have been out of my house and just returned now. In fact the broken cap is still working and I have used it today with no problem despite the fact that I just make 20-30 kms each time and have to mount and dismount properly until a new one replace it.
The gap of the filler neck is around 19-20 mm and I will follow your recommendations to replace it and to mount the foam seal. Thanks again for your informations.


ALFREDO SIMOES

Alfredo,
was your car standing unused for a good while and/or do you not use antifreeze/coolant or the antifreeze/coolant hasn't been changed for a good few years. All a bit unusual to me, but that might just be my lack of experience in this area.
Nigel Atkins

In this part of the year I use the car on the weekends for 20-30 Kms but on winter it is possible to stay for 2-3 weeks stopped. I don't use coolant but there is no lack of water in the radiator and water is clean
ALFREDO SIMOES

It's always advisable to use antifreeze as a coolant even when you have no risk of temperatures reaching zero, as plain water will cause internal components to rust and silt to form which can block passages. If you remove the radiator cap - carefully - with the engine warm and the water is orange then you have rust in there. This settles out when the system is cold and is not visible in the radiator neck.
paulh4

Thanks Paul for your information. In fact it is so easy that I will put the antifreeze. I was not warned to the fact that when cold the eventual rust would be deposited. Thanks again for the information.
ALFREDO SIMOES

I was going to put the same as Paul, I will now add don't just add antifreeze, check as Paul suggested and if required a proper clean of the cooling system.

The antifreeze/coolant also lubricates the system so should be changed every couple of years.

If you need to clean the cooling system I have a very simple but thorough method that has three stages for you to chose how far you go with it.

I would add a single journey of 30km is barely enough to get the oils flowing and systems working and putting the starting charge back into the battery(ies). 20km is barely enough to get it fully ready for proper driving using the gears, brakes, steering and tyres on longer enjoyable runs, these cars were designed and built for everyday enthusiastic use.
Nigel Atkins

Forgive me if you already know this, but going from water to antifreeze needs a bit of care, even though you don't need the cold weather capability. There is usually quite a bit of old coolant left behind which will dilute the new, if you just use ready-mixed.

Drain the system as much as you can - quite warm if you have a radiator tap as that will flush a lot of the sediment out. If no tap then it will have to be the bottom hose at the radiator so needs to be cooler. There is a tap or plug on the distributor side of the engine but few people can get anything out of that.

Then put the required amount of neat anti-freeze in - needs to by , then top up with water. Run the engine, and it helps if the front of the car is higher than the rear, topping-up with water as needed. For the first couple of times it is run up to temperature and cooled again top up with water if needed, but thereafter top up with ready-mixed anti-freeze.

Keep an eye open for any leaks from hoses etc. as anti-freeze tends to leak out easier than water.
paulh4

Thanks for your most useful informations on this matter and you are right, because I am completely blind on mechanical issues. So as I am afraid to intervene in a wrong way, I use to get professional aid on that despite I usually tend to see what they are doing, and that is what I am going to do. Fortunately that is not too much expensive here in Portugal.
ALFREDO SIMOES

Alfredo,
if you have not already got a copy then if you buy and read the relevant Driver's Handbook you will know more about your car than many even long term owners. This is not the workshop manual but covers servicing and maintenance as well as what the driver needs to know about the car.

Ref: 0052 - https://mgownersclubstore.co.uk/catalog/Online_Catalogue_Handbooks_5.html

Example of contents from my midget Driver's Handbook below.



Nigel Atkins

Alfredo
The same thing happened to my pressure cap. I kept on using it for years in pieces. It was rated at 7 psi but apparently it should have been 10 psi. I replaced it eventually with another from David Manners but the spring looked much stronger even though it was still rated at 7 psi. I was getting leaks from my heater valve and bottom hose which I never had before. I ordered a 10 psi one from Gates thinking they were a reputable supplier. Turns out that all radiator caps appear to be made by Presco in Worcester. I've gone back to the first 7 psi one from Manners and cured the leaks.
I've also recently fitted a Revotek electric fan and removed the mechanical fan. The gauge shows the engine getting pretty hot but I've not had it boil up yet. I decided to turn the thermostat down a little and put up with the fan running more often. There is no doubt that when its running it cools things down but I can see the drop in voltage (top end of the green band on my gauge to the bottom). I also fitted a standard 82 C stat instead of the 88 C I ran with the mechanical fan.
Paul Hollingworth

My 1973 mgb roadster was running OK during the cooler weather but as soon as we got a few hot days the temprature gauge went into white section and radiater boiled over, I am now in the process of flushing the system. I run the engine until it was at full pressure then removed the engine block drain plug expecting water to come gushing out but no, a bit of gunge came out but no pressure. I screwed a hose attachment into the drain plug hole with a hose connected, in theory water should have went through the system and come out at the radiater. can any one tell me why that didn't happen, full pressure from the tap into the engine should have cleared it. John Cook.
JG Cook

The number of engines where the block drain plug works can probably be counted on one pair of hands. Some have been found to be blocked with casting sand i.e. blocked from the factory.

This is one of the rare cases of true overheating I've come across, 99% of people of complain of overheating are only getting the temp gauge going a bit higher than they think it should. If it's not losing coolant, it's not overheating, and yours does seem to be.

That can be down to two things - a) the engine producing too much heat, and b) the cooling system failing to get rid of it. There can also be a third where the the head gasket fails but I'd expect that to be more obvious from many air bubbles in the radiator when run with the cap off and oscillations from the temp gauge.

The first thing to do is feel the radiator as it is warming up from cold, to check the function of the thermostat. It should warm very slightly as the temp gauge is rising towards normal, then suddenly get pretty hot as the stat opens. If the radiator doesn't get hot then the stat is stuck closed, and it will boil. It will boil with a stuck stat in cooler weather as well, but maybe it's only recently completely stuck.

If the rad is getting hot then check the surface all over, and the bottom hose. Any cold spots in the rad with a hot outlet indicate the rad has blockages.

If the rad is hot at the top and cools rapidly as you work down, then either it is completely blocked or maybe the pump isn't circulating coolant as it should, the vanes can corrode and even spin loosely on the shaft. There could also be major blockages in the block and/or head.

If the rad is hot all the way down and the outlet is hot as well, then it's more likely that the engine is producing too much heat i.e. more than the cooling system can get rid of. Check ignition timing and carb setup, although I'd say that problems there would be unlikely to cause boiling over unless there were obvious running problems (i.e. in addition to the boiling) as well.
paulh4

John Cook,
part of my simple thorough method is to drain the engine block whilst using a piece of thick wire to clear out the crud that collects at the engine block drain hole at each draining of coolant, cleaner and when flushing out.

I know some say it's a waste of time but it's very simple, easy and free to try and it can have effect. If you're getting nothing through at the moment and by cleaning you get some clearance that has to be an improvement.

As you screwed a hose attachment into the drain plug hole you would probably be one of the very few that would actually appreciate my simple thorough cleaning method, if you want me to send you a copy just ask.

Cheers.
Nigel Atkins

John Cook lvk25l@yahoo.co.uk
RE-Overheating.

Further to my MGB over heating problem, Thank you Paulh4 and Nigel Atkins for your replies and advice.
I have flushed the system out 3 times using Holts & Wynns cleaner even driving short distances with it in then flushed via the heater pipe on top of the engine after each cleaner through the heater, engine block, radiator, clean water out of the radiator top. During hot days gauge went up to the white section but didn't boil over, today Friday warm wet day did 8 mile round trip, gauge stayed half way between O & N moved to N while ticking over on arriving home, so all of this seem OK. Now while doing this I have been driving with the engine block drain plug out hoping a gush of water would exit from it but no, I have been getting a bit of gunge and clearing it using Nigel's wire suggestion, today a bit more gunge followed by trickle of water and I mean trickle! I will continue doing some short trips with plug out but pressure at that point seems very little. (I am carrying a container of water and the plug in my boot just in case. John Cook.
JG Cook

As you seem to have solved the problem now I'd put the plug back and forget about clearing that drain, just drive and enjoy it.

It really dates from pre-antifreeze days when people drained their systems on cold winder nights and filled up again next morning. In the normal course of events the times when that drain might be needed for other reasons is very limited. At the bottom of the water jacket it's in the coolest part of the engine, so coolant there isn't doing much anyway.
paulh4

I am always about driving the cars (and would always try to avoid a journey of less than 20 miles) so totally endorse what Paul has put about driving the car to enjoy it.

On the other hand I like to do a real thorough job once so that in future it's just routine simple maintenance.

If there's any crud/muck in the system I prefer to get it out where reasonably possible as I like to drive my classic in a spirited way so want all the safety, protection margins I can get because let's face it there's often something in some system that plays up with our old cars.

I like to deal with the system in sections as far as flushing, back-flushing and flushing and concentrate on removing as much residue in the system at each drain and flush of coolant, cleaner and flush fluids as that also takes out as much muck/crud as possible. So I would be draining and clearing out the drain hole and fluid residue in the block as a section.

As the plug is already out and if the drain hole is still partially blocked I'd try a stage up from the wire and use a drill-bit or extractor bit rotated by hand (if you can get in there, sorry can't remember how much space there is) to, er, extract any crud/muck I could.

I fully realise this is just one section and aspect of the cooling/heating system and other elements and components affect the overall, er, effectiveness of the system, one being the accuracy or not of the gauge reading and worrying too much about an over narrow expectation of what the reading should be.

Nigel Atkins

From what I remember with mine out as soon as you get through the outer wall there is a cylinder wall. The passage turns sharply round that and it's narrow, no chance of using any kind of bit in there, hence tales of chiselling down from above with a hard rod. It would be interesting to see a block with the top half of the cylinders sliced off.

Despite being blocked mine has never given me a moments worry in the most trying of conditions.
paulh4

With the drill or extractor bits I was only thinking of the drain hole and the cavity behind it to try to fully open that aperture so that more crud/muck gets out through that hole rather than backing up behind an obstruction there and if so inclined poking around further back and round with the wire to loosen more crud/muck to get it out.

I accept that it might not be necessary from the experience of others and only suggest it as it's easy to do and might save further work down the line.

I loathe, l-o-a-t-h-e, doing any work on my car, horrible, messy, dirty and generally unsatisfying for me, if I still had the money and could find reliable, good quality mechanics to do the work I wouldn't lift the end knuckle of my smallest digit on my car other than driving and driver's checks.

So I'm one of the last owners that goes looking for extra work on these overpriced old cars called classics and don't have the reverence to marque or history that some have on the forums but I do accept some maintenance input is needed to actually drive these cars in a spirited way as they were designed and built to be used.

It's different strokes for different folks.
Nigel Atkins

Just for info, the vertical drilling from the water jacket to the drain plug hole is in the back top corner of the tap hole. The rust that settles there is deprived of oxygen and it turns into a solid black oxide plug. The way I clean them out is from the top after the head is off, using a long 1/4" masonry drill on hammer action!

The space in the water jacket behind number 4 cylinder is actually one of the hottest places in the engine block as water flow there is low. It is not unusual to find casting sand or even lumps of cast iron trapped in that space.
Chris at Octarine Services

This thread was discussed between 30/06/2019 and 10/08/2019

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