11 replies to this topic

[adv123]

Hello folks,

 

I have a '97 MPI with a weird cooling problem!

 

The coolant is expanding in the expansion tank and leaking but the temp gauge suggests that the engine is not overheating. I'm pretty certain the gauge is working because the mini was overheating earlier this year due to a seized cooling fan. I replaced this and at that time flushed the cooling system, fitted a new temp sender and a new thermostat. The fan still cuts in as required but with the engine running at normal I still have this issue with the expansion tank overflowing. Any ideas?

[Fast Ivan]

try a new cap, very common fault with the MPI's

[adv123]

Actually I should've said that I changed the cap too! However after your suggestion I did just try a spare one I have and again from a cold start I can run the engine up to normal temperature and after 5 minutes or so sitting idling, the expansion tank begins to bubble and the fluid expands and starts to force itself out of the tank? The radiator and all the pipes are warm so fluid is passing round the whole system.

[Fast Ivan]

well that's the cheap option ruled out if you are confident about the cap, the tanks are also known as a week point, can you identify where the leak is coming from?

[adv123]

I'll have a look, thank you. It's a weird problem, I mean the tank should be large enough to deal with any expansion of the coolant but it's actually boiling. Bit lost I'm afraid but I will check the tank

[Yoda]

Time to check head gasket for leaks i think?

[pdaykin]

If you are sure that the gauge/sender are ok it sounds like you have air in the system - the air doesn't transfer heat as well as water so the sender doesn't think that the engine is hot.

Does sound like it could be a head gasket or the head itself

[adv123]

I have checked for air and all seems ok. Also there is no trace of oil in the water. I am beginning to think it might be an idea to get the head off and have a look though.

[adv123]

After some research I think I'm dealing with what is called after-boil. When the water pump stops circulating the stagnant coolant starts to boil up. Oh I should say thanks for the help and advice guys - much appreciated.

[retrohire]

HI Everyone,

 

We have 2 MPI minis a Paul Smith and and a Sportspack on our rental fleet that have both recently had overheating problems with the temp guage showing normal but the coolant boiling over. I would agree with everyone who says first thing to do is change expansion tank cap for a minispares one in our experience all other ones are useless. This didn't cure the problem for either car and we were convinced in both cases that the head gasket needed replacement so the head was taken off the Paul Smith skimmed ported and replaced with upgraded ford washers and a proper gasket set after doing this twice , the car still boiled over with guage on normal  so as a last resort we changed the radiator which looked to be working properly. Hey presto no more problems, if the radiator is blocked or obscured then the water does not get to the temperature required to turn the fan on 102 degrees C and boils over. The sports pack was even worse boiling over within about 5 mins of start up from cold and again a replacement radiator from minispares approx £ 70 cured the problem.

[1275GTS]

i had this with my spi cooper. i replaced the radiator as it was possibly the original one and looked really worse for wear. I have had no issues since then (over 3 years ago). as a precautionary measure i did replace the water pump as well.

[Ethel]

The pressure cap should push the boiling point up to 120c, so the gauge need not be under reading.

 

If it is the head gasket, it may well pressurise before it gets anywhere near boiling, squeeze a hose.