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E85 / E86 Z4 (2003-2008)
E85 Z4 Roadster, E86 Z4 Coupe, E85 Z4 M Roadster, and E86 Z4 M Coupe talk with our BMW gurus here.

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  #1  
Old 07-08-2014, 05:49 PM
Xtrs87x Xtrs87x is offline
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Cooling problem :-(

So I have an 05 z4. I recently bought it and it overheats. The first time it was overheating I saw that there was coolant all over the coolant expansion tank, so I ordered it and put it on. Just drove it and it's still overheating. Open the hood and there is coolant leaking from somewhere near the expansion tank. The engine only seems to overheat when I rev it really high. What can the problem be?
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  #2  
Old 07-08-2014, 06:50 PM
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pungo pungo is offline
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Mein Auto: Z4 coupe, Corrado
Are you saying it never overheats if you drive normally without high revs
? What are really high revs? hitting Rev limiter often?
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Old 07-08-2014, 07:23 PM
Xtrs87x Xtrs87x is offline
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I only drove it for like 10 minutes. Once it was warmed up I hit 6-7 rpm thats when I saw the temperature gauge go up. The rest of the time I was crusing at 50 and it was late in the day so it wasnt hot anymore. When I pulled over and opened the hood it smelled like burned coolant? (Not sure) and I saw it leaking somewhere around the expansion tank.
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  #4  
Old 07-08-2014, 09:26 PM
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pungo pungo is offline
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Unless you know what you're doing, you should probably take it to a reputable shop to diagnose the problem before you cause severe engine damage $$$.

If you do know what you're doing, pressurize the system and check for leaks.
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  #5  
Old 07-08-2014, 11:35 PM
Clearancediver Clearancediver is offline
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Likely the o ring in the hose connection to the expansion tank is leaking. You should either replace that hose or remove/lubricate/replace as a minimum.


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  #6  
Old 07-11-2014, 07:29 AM
Vladi Vladi is offline
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Mein Auto: Z4 M (2007)
1) What's the level of coolant in the expansion tank?

2) If you have a temperature gauge on the instrument cluster (not sure if the other models have it, the Z4 M does not, it has only an oil temperature gauge) - what's the behavior of the needle? Does it move towards hot faster than the usual once you start the car cold?
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Old 07-11-2014, 08:56 AM
Xtrs87x Xtrs87x is offline
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Problem is fixed. It was the coolant expansion tank cap. It wouldn't overheat when it was just turned on but once I hit the pedal it would start pouring out from the pressure. Cap was damaged. Glad it was an easy fix.
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  #8  
Old 07-11-2014, 11:08 AM
Mikey48 Mikey48 is offline
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Glad you got it fixed ! Enjoy !
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  #9  
Old 07-12-2014, 01:33 AM
Vladi Vladi is offline
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Great news! But keep an eye on it for a while - damaged cap might mean damaged thread/bayonet of the expansion tank. So a new cap in this case does not solve the problem.
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