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MG MGA - The Perennial Overheating Question

My Mk II recently began overheating when the car is at idle. I live in Houston, which can be tough on these cars, but I had been driving the car in temps up to 95F without problems for about 2 years. The problem came on somewhat abruptly, beginning to overheat at stop lights. The car will hold 190F while driving.

I'll check the thermostat - only has 1000 or so miles on it. Can I just pull it out ? Or do I need some type of blank ?

engine rebuild also is only at 1000 miles or so, block was boiled at that time. Radiator is pretty old though.

Anything else I should check on ?

Thanks,
Chuck Mosher
Chuck Mosher

Chuck-- there is a whole bunch of stuff on this subject in the archives, but the usual things to check in addition to the thermostat are fan belt tension, timing and fuel mixture. One easy way to check the thermostat is to take it out and put it a pan full of water and heat the water- it should open before the water boils-- if you have one of those kitchen cooking thermometers, you can read the temperature that it opens at.
good luck/ gil
gil

Hang on.

Check the red plastic shoulder on your points first. If this is worn, your timing will advance very gradually till it becomes a problem and produces just what you describe. It's an easy visual check you can do without using a spanner.

If you have a duff thermostat, it will not warm up, as they are designed mostly to fail "open" these days. If it has failed closed, the car will overheat even when driving. It's therefore unlikely to be a thermostat problem.

I have the reverse problem, the thermostat is fine, but car is taking forever to get up to 60 degrees C, and an age to reach 70C, and only when I have a large passenger going uphill do I make 80C. Who ever heard of an A that refused to heat, let alone overheat?

dominic clancy

If a sudden change, look for things that break. A bad water pump impeller come loose, broken points, a hung up breaker points rotating base plate, something come loose within the radiator or block which could plug up a bit of the core (like an internal baffle, if there is one, or even a baffle inside the muffler (if it is old and rusting) which could be blocking the exit inside the muffler or a chunk of which could have gotten wedged in the tailpipe.

Most overheating problems don't start suddenly as they are usually related to things which either result from long term deposits or setup problems. If a long term problem you will usually see changes in operation build to a point where it overheats over time. If a setup problem, you usually know about it immediately after whatever work you have done to change things.

Mystery problems, however, which seem to happen suddenly and for no explicable reason, are usually unforeseen mechanical or electrical failures.
Bob Muenchausen

"check in addition to the thermostat are fan belt tension"... Just be sure that you don't overtension the fan belt or the next problem you will be facing is a genertor that doesn't work. With a generator equipped vehicle, there is not the drag created by current draw as there is with an alternator and the fan belt doesn't need to be real tight. See my article regarding fan belt tension at: http://www.omgtr.ca/technical/tdtf_fan_belt/loosen_up.htm
Good luck - Dave
David DuBois

How are your radiator hoses? Old hoses can deteriorate and partially block the flow.
R. L Carleen

Hi Chuck,

I posted this question earlier this year and had over 50 replies, each with very useful suggestions.

I'm sure if you search te archive youwill find it, the thread was titled, All out of ideas - overheating.

I'm still working my way through the ideas, improving my A with every job.

Roy.
R. Maher

This thread was discussed between 30/10/2005 and 31/10/2005

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This thread is from the archive. The Live MG MGA BBS is active now.