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Randall Voss
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Discussion Starter #1
Need some advice from the experts and those who have traveled my same road. I apologize in advance for the length of this post - I wanted to be pretty specific about what I'm experiencing.

2008 Clubman, N12 (70K miles) had major leak in thermostat housing and engine went hot enough before shut down that the seal grooves around the center 2 bolts in the valve cover distorted.

I replaced the thermostat and housing along with water pipe which also had some deterioration where it meets the water pump housing and a lot of sludge buildup in the tube. Had to use RTV sealant on valve cover to keep #1 & #2 spark plugs free from being surrounded by oil.

Having read numerous posts here about bleeding the air out of the system, and having talked to the service manager and a mechanic at BMW dealer, I am still getting air in the system.

I have bled the system with heater on, waited for coolant at bleed screw and then topped up reservoir. After a drive I find heater starts to loose heat. Open hood and reservoir is now full with both upper and lower radiator hoses rock hard until I again let the air out of the bleed screw and then reservoir drops to normal level.

Also as I drive, sometimes temp warning will come on and then go off shortly. Sometimes it will not come on at all. It acts like the thermostat stays closed too long and then problem clears when it opens.

Why can't I keep the air out? Is it possible that head gasket is allowing compression gases into cooling passage? Have I possibly reversed the upper and lower hoses at the thermostat housing? Water pump no longer pumping?

Confusing part is that system never seems to overheat and stay overheated. Warning light always goes off after a few seconds but reservoir gets highly pressurized.
 

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It sounds like when it overheated you might have warped or cracked the head especially as its got hot enough to warp the valve cover. The first thing I would suggest is go to a garage where they can check your coolant for combustion gases
 

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Randall Voss
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Discussion Starter #3
I was thinking maybe head gasket. Engine runs fine and there is no evidence of oil and water mixing. And I don't know where I would go here in Hawaii to have coolant checked for combustion gases. Is that something a BMW dealer should be able to do?
 

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A garage can either do a compression test on the engine to see if a cylinder is reading low pressure, or they can pressurize the cooling system to above normal operting pressure and see if that leaks off, or do a sniff test on the coolant to check for combustion gases in it, all these would test for possible head gasket/head casting failures.
Sometimes there will be no evidence of water in the oil, it depends on where abouts the gaskets etc have gone, if it has.
 

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Randall Voss
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Discussion Starter #5
Had a great discussion with service guys at local BMW dealership. They were incredibly forthcoming with advice and discussion. I then went to NAPA to get the tester to check for combustion gases in the coolant. If the answer is yes I am then going to loosen and attempt to re-torque the head bolts. According to BMW, overheating of their aluminum block engines often leads to pulling the head bolt threads out of the block - ouch. Then I'll be looking for a replacement motor. Service guy told me he has never pulled a mini head but has done engine swaps. He is waiting for a used motor for his personal 5 series for the same reasons.
 
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