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Discussion Starter #1
Hello,

Some advice please for an overheating mini one 2003 petrol. The water/coolant is boiling in the expansion tank at 95 degrees. There is no bubbling until it reaches this temperature at all. Cant see any leaks at all and the level doesnt drop. Top and bottom hose are hot so im presuming the pump/stat and rad are circulating ok. Is this likely to be a blown head gasket causing the loss of pressure at high temperatures causing the lower boiling point ? There is no sign of oil in the coolant or vice versa but im guessing it could be between a water jacket and cylinder ? Anyone had similar issues like this ? Thanks
 

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A blown head gasket (or other failure between the combustion chamber and the water jacket) doesn't cause a drop in pressure in the coolant. The combustion pressures are far higher than that of the coolant system so causes excessive pressure in there. This can be felt in the hoses. It can't cause the coolant to boil at a lower temperature than normal either.

With the car running and hot do the hoses feel firm when you squeeze them?
 

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Discussion Starter #3
A blown head gasket (or other failure between the combustion chamber and the water jacket) doesn't cause a drop in pressure in the coolant. The combustion pressures are far higher than that of the coolant system so causes excessive pressure in there. This can be felt in the hoses. It can't cause the coolant to boil at a lower temperature than normal either.

With the car running and hot do the hoses feel firm when you squeeze them?
Ok thanks. Yes the hoses are firm to squeeze when its running and hot. What do you think could be the causes ?
 

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There's a good chance of a failure between the combustion chamber and the water jacket as you were suspecting. Does the exhaust have excessive whitish 'smoke' too? I'd be doing a sniff test of the coolant for combustion gasses at this point.
 

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Discussion Starter #5
There's a good chance of a failure between the combustion chamber and the water jacket as you were suspecting. Does the exhaust have excessive whitish 'smoke' too? I'd be doing a sniff test of the coolant for combustion gasses at this point.
Thanks Gary. No smoke. Ill keep my fingers crossed its just the gasket and not the head which is bad! I bought the car as a hobby project to do with my nephew so he will be happy we get to do more work.
 

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Discussion Starter #9
Small update as not had lots of time to work on it. Got a coolant pressure tester and it holds the pressure at 1.1 bar for over an hour. No visible leaks. Tried a " sniff tester" in the overflow tank and this was negative as well, so its not putting combustion gases into the coolant. Any ideas please guys ?
 

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Discussion Starter #12
Forgot to add....also did a compression test of all the cylinders for good measure. They were all 122 to 127
 

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275947

Well decided to go for removing it and getting a better look. The cooling jackets dont look corroded and nothing stood out with the gasket. Theres a lot of dry coolant but im guessing thats normal ? Ill be taking it to a machine shop this week for their opinion so fingers crossed. There is some discolouration on the inside at the exhaust manifold side. Should that be something to worry about? Cheers again for all the advice guys
 

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Discussion Starter #15
276030

Head skimmed and rebuilt. Put it all back together and ran nicely.....until it hit 95 degrees and started to boil again in the overflow tank.....noooooo. So after all that ( cant complain too much as i enjoyed doing the rebuild) it still has the same issue. Any ideas anyone ? Im refusing to give in haha
 
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