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MG MGA - engine temp

My MGA temp always gets up to near boiling at anything over 70 degrees ambient. Just how hot do people reckon is normal for these cars? (I have not so far had vapour lock but have a Xflow head so carbs on other side from exhaust. Have that problem acutely on my 1950 MM Minor though!)
H L Davy

There's loads of stuff about engine temperature in the archives and running temperatures seem to vary greatly. As far as I can tell, 'normal' would seem to be 190F, but after-market radiators, grilles and modern fuels can push 'normal' up considerably. If you are not literally boiling over, don't worry. Your engine will not explode or melt if the gauge reads 230F, and it will run quite happily at that temperature, at least mine has, I wouldn't have known it was running hot if I hadn't looked at the gauge.
Some of the things that can make the engine run hot are, retarded ignition, faulty thermostat, inefficient radiator and grille slats too 'closed'. My new radiator (from MGOC) was hopeless at cooling the engine, and it routinely ran at 212F in warm weather. The 'Bob West' radiator I now have, is much better, and it runs at 190F most of the time when I am moving. A coolant recovery system is a must if you haven't already got one.
So basically, I would say that 'normal running temperature for an MGA these days is anywhere between 185F and 220F. If you see steam or the temperature goes above 230F while you are on the move, STOP!
Lindsay Sampford

Do you have the correct radiator cap?
dominic clancy

Although I must admit my car doesn't wear one, an MGA owner just recently told me that the felt attached to the bonnet above the radiator, was a great help in keeping his engine cool. Do you have one in place?
Graham M V

Lindsay's comments are spot on and reflect my long experiences with MGA's. Just make sure that you do not run out of coolant. Anything above the thermostat rating means that the cooling system is not being controlled. Many years ago we bought a new Mini (for my wife) and the temp gauge remained rock solid somewhere in the middle of the dial (presumably at the thermostat setting), searing-hot days or biting-cold, for the many years that we owned it despite the small radiator which was tucked under a wheel arch! Frustrating! I think that it has something to do with repro (and factory?) MGA grille slats, very little air seems to come through the heater unless the blower is on?
Barry Bahnisch

Graham, I honestly do not know if the felt helps, hurts, or does nothing. I I do know that I never had any overheating issues in 32 years of driving without one. I put one in my latest MGA when I had an overheating issue. The solution ultimately was buying a new three-row radiator. I have since removed the felt thinking it may restrict total air flow within the engine bay. To say it's a great help is definitely an overstatement in my opinion.
D Quinn

I think the felt wad is there to force the air through the radiator! Not to let it slip around and over the top where it has no cooling effect.
Barry Gannon

Barry, I agree, that was the felt's designed purpose.

But air flow was not the science it is today. For example, the idea of the bonnet vents was to let hot air out and wind tunnel testing proved they did just the opposite.
D Quinn

Thanks all. Lindsay you describe what I get very well. I did in fact overheat due to a water leak and had to have the head worked on. Fortunately it seems undistorted and now ok. In the process the end of the temp sender melted and I have temporarily fixed another gauge which reads in centigrade usually 90/95. On my minor 1000 it's always steady at 70. Do not have coolant recovery how does one check the coolant level and top up with such fitted? I removed thermostat entirely and fitted sleeve as advised by Moss. What is correct radiator cap? Does modified rad need more space? (I have an oil cooler in front of the rad.)
H L Davy

HL, MGAs do tend to discard a lot of coolant over a short period of time, which I reckon leaves the top hose half-full, which much reduce the ability of the coolant to circulate properly. A coolant recovery system solves this problem, and is dead easy to install. See the archives or Barney's site for details. The coolant level in the overflow tank can be checked even when the system is hot, as it is not pressurised, so if the overflow tank has coolant in it, your rad is full to the brim. I'd advise you to fit a thermostat. Running without a thermostat can do more damage than running hot. In cooler weather you will be doing a lot of miles with a 'cold' engine and oil does not circulate properly until it is warmed up. My rad is a standard shell, but has a more efficient core design. The correct rad cap is a 7lb one. If you have a standard MGA radiator, make sure you use the correct long-reach cap. If you fit a modern type 3/4" reach rad cap, you will not pressurise the system and it will boil at 212F. With the correct cap and anti-freeze you will not boil under 235F and everything will be lovely whilst the needle is on the water scale (apart from the occasional bout of vapour-lock if you get stuck in traffic!).
Lindsay Sampford

Wow thanks again Lindsay. How deep should the correct rad cap be?
H L Davy

Hugh, the rad cap should be an inch and one eighth from the inside of the top flange to the rubber seal. The standard rad filler orifice is 1" from the flange to the seal step, so your rad cap spring compresses by 1/8" to give the system pressure.
Lindsay Sampford

In my experience, a hot running engine is usually caused by a huge build up of scale and gunk in the back of the engine block. The area around No. 4 cylinder is a very dead area for the water circulation and it tends to collect an enormous plug of almost solid crud.

In the good old days it was expected you would drain and refill the whole coolant system at least twice a year because the anti freeze was hopeless. These days the stuff usually stays there for ever.

The proper solution is to have the block hot tanked but it is impractical on an otherwise good engine.

I have managed to clean out two blocks in situ by taking off the head and removing the water drain tap and (literally) bashing the crud through the holes in the block with a long screwdriver and a light hammer until it is all broken up and washing it out of the drain hole. First I have had to carefully drill out the drain hole with a 1/4" drill.

A useful tool is one of those pump up garden water sprayers to help jet the crud away.

The effect is nothing shot of miraculous. A good 20 degree improvement.

It is possible to get an idea of the state of your block by attempting to drain the block from the rear tap. My guess is it will be absolutely solid.

Lindsay, if you are loosing coolant like that I would look at a small head gasket leak between the cylinder and water jacket, probably between 2 & 3 cylinders. the only water loss you should see is a brief loss on the first time out after filling, as the filled level equalises with the expansion of the water.

The right rad cap is a 1" reach (Moss (UK)Pt no GRC103) at 4lb but I wouldn't hesitate to use the GRC101 at 7lb


P Reardon

Paddy, I don't lose ANY coolant!!
Lindsay Sampford

I agree with everything that Lindsay has said. My 1600 Coupe runs happily all day between 190-212 F depending on the outside temperature and terrain. At the Reno 2011 event recently it even went over 230F when I stopped the car after a long run up to 9000' over Mount Rose. The car quickly cooled to 190F on the way downhill. The car did not overheat and if you didn't have a temperature gauge would know no different.

Andrew Preston

Andy, yes, I've seen that plenty of times after switching off (Barney has seen that while on the move! ). Did you feel how hot the hood/bonnet was? When my gauge reads like that, the bonnet is so hot you don't want to keep you hand there, and I get burnt fingers when I touch the bonnet prop!
I don't worry where the gauge needle sits now. As long as I see it occasionally move downwards I know that everything's OK. The time to start worrying is when it only moves in an upward direction!
Lindsay Sampford

I agree with what Paddy experienced. I just got through rebuilding an 1800 engine for my A and the water jacket area behind the drain tap had to be thoroughly cleaned out due to compacted junk and rust globs. Not only that, I had to run a long drill bit down two of the water passages that come up to the head, in that same area. Their internal diameter had decreased in size due to corrosion to about 75-80% of original size.

I even considered running Muriatic acid through all of the water jacket but guessed I might create more problems than I cured.
JM Morris

This thread was discussed between 23/08/2011 and 27/08/2011

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