Spontaneous Max Overheat during Idle in Hot Nebraska Parking Lot - BMW Forum - BimmerWerkz.com

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post #1 of 3 (permalink) Old 07-19-2011, 05:13 PM Thread Starter
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Spontaneous Max Overheat during Idle in Hot Nebraska Parking Lot

I have asked another board but just wanted to ask you guys to, so forgive me, if you follow both.

I am already freaked out that this is a cracked cylinder head but let me just post what happened. I am driving through Nebraska and got a call so instead of staying in the restaurant and taking the call, I jumped into the car and idled and had the AC running for 20 minutes in the noonday heat. I noticed the AC was off and just the blower/fan and then noticed the temp was not in the middle, like always, but in the red, with the light on. All the way in the red. Instead of turning the car off, I started driving to get some air in it and it got worse, so I stopped the car, opened the hood, and there was coolant all over the inside of the hood/bonnet. The temp gauge went all the way to hot and turned off, actually. And stayed all the way right. I had a rural mechanic come over and look at it and it had cooled but there was no coolant in the reservoir. I drove 1/2 mile to the garage and their first diagnosis is a crack in the Radiator Coolant Overflow Tank, which I will replace, so they can do the test to see if it is, in fact, just that crack or if the pressure backup from a cracked cylinder head. What is your intuition. I know that I should not have been idling in 100F heat in the car with the AC on -- and I also know that I should have turned the car OFF when I saw the overheat and left it there for at least 1/2 hour. But I didn't. But I will do from now on. What does your intuition say? Replace the Radiator Coolant Overflow Tank or the whole engine?
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post #2 of 3 (permalink) Old 07-20-2011, 07:03 AM
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Welcome to the Werkz.

An expansion tank isn't a huge expense, start with that if its cracked (which they do after aging). If the engine still had coolant in it it, check the engine oil to see if its contaminated with coolant. If not, get the whole cooling system pressure tested and see what comes from that. Expect the worst and hope for the best.

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post #3 of 3 (permalink) Old 07-20-2011, 09:29 AM
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Test for CO2 in the radiator (or is that CO)
Done with a colour changing liquid
The one I used went from blue to yellow very quickly as I definitely had a crack in the head. Also blowing bubbles in the tank.

Also after topping up the system and leaving it to sit for a day or so, disabled ignition and fuel pump, removed spark plugs turned engine over and watched water come out of No 5 cylinder. Good indication.

As Bretski said look for water in oil also look for oil in water.

My daily is a Mitsubishi HSGR (but I wouldn't mind an e34 525i)

Last edited by Penngwyne; 07-20-2011 at 09:31 AM.
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