MG Car Repair: MG Midget repair

Question
Head temp rises after engine shut off. Engine won't start until head temp goes back down somewhat. Could sparkplug temp rating be causing problem?....thanks..

Answer
Hi Joe.

No, I don't think it is anything to do with the spark plugs.  It is quite normal for the temperature on the gauge to go up a bit immediately after switching the engine off.  The water pump is no longer pumping, so the heat still in the engine comes out as a temperature rise.  If the park plugs are too soft, you will usually hear some pinging under acceleration.

First thing to do is to check that the fanbelt is not slipping.  With the engine switched off, you should NOT be able to turn the cooling fan by hand.  If you can, then the fanbelt needs tightening.

Also, I have heard a lot of reports recently from the USA about fuel vaporisation.  Has American gas changed recently?  Are they adding more Ethanol or Bio-Ethanol to the gas?  If your heat shield is missing or damaged then the heat from the exhaust headers could be causing the fuel in the float chambers to boil when you stop with a hot engine.  After a while it cools down, and then the engine will run normally again.

/============ UPDATE ============/

The best way to solve this problem is to remove the mechanical cooling fan from the engine and fit an electric fan instead.  You can wire it so that it continues to run after you have switched the engine off, or fit an over-ride switch so you can turn it on after you have stopped.