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MG MGF Technical - Thermostat

What if any thing would cause the temp guage to hit the top, the expansion tank to fill with coolant enough to activate the pressure relaease on the cap. I am guessing the thermostat did not open when it should.
Nkosi_Ecosse

HGF?, but I hope for your sake it's not. (HGF = Head Gasket Failure). When the headgasket fails it can create high pressure in the cooling system. This is because the head gasket breaks its seal and gas escapes into a number of areas in the engine. This usually pops the pressure cap.
Here are some things to think about.....
Did the front radiator fans turn on at all?
Did the engine bay fan turn on?
Check if the engine oil is clean and that there are no signs of creamy "mao" in it.
Check to see if the coolant fluid is clean and that there is no oil in it.
Have a workshop test for HGF. They do a chemical test.
Don't let the car overheat again until you can sort this out.
or if you're lucky, maybe its just a stuck thermostadt.
Cheers,
Branko
Branko

What if it was the cap that failed first, lowering the system pressure, coolant boils etc. High temps in the system could have been the starter so any of Branko's fan checks etc are worth doing - caps are only about a fiver but you may need to bleed it if it dumped a lot of water. Good luck and hope it's not you know what.
Tony

The first thing to do is to get it to a garage and stick an exhaust sniffer in the expansion tank - HC's in the tank are game over.

It could be a sticky thermostat, but they are a bugger to get to, you will need a good quality ratchet spanner from halfords (call back if you want instructions)
Will Munns

I had a problem with a sticking thermostat on my F a few months back, initially it just caused the temp gauge to rise one notch in traffic then returned to normal, of course when it went into the dealer it couldn't be traced because all was working fine. Finally it stuck completely and the temp gauge shot from normal to hot in about 5 seconds. Thermostat was then replaced! If its is HGF, that should be reasonably easy to spot for an experienced MGF mechanic, as oil/water mixing is evident.
Mike

The oil is fine and the coolant looks OK, the problem first started with the engine revving high and missing, then flooding, due to (I think) the ECT sensor having a dirty connection on the plug. Pulled the plug off and give it a bit of a clean and refitted teh plug was going to try it out but the cap operated while I was busy revving the car with the throttle linkage. I guess putting into the garage might be the best idea, mmnn still 4000 miles short of its next service. Good job I made a bit of overtime last month.
Nkosi_Ecosse

Here are some things to think about.....
Did the front radiator fans turn on at all?

Yes it did.

Did the engine bay fan turn on?

Yes it did.

Check if the engine oil is clean and that there are no signs of creamy "mao" in it.

The oil is fine, definatley no salad cream.

Check to see if the coolant fluid is clean and that there is no oil in it.

The coolant seams fine.

Just took it for an eighteen mile round trip both town and some motorway. Tenp guage stayed where it should and always was usually just one notch under half. Oil temp got to 120 where it normally always sits car is responsive enough and no funny noises. I think I'll still have the system pressure checked just to make sure.
Nkosi_Ecosse

This thread was discussed on 26/07/2005

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