# Multiple E39 Overheating Problems



## pde39 (Jun 27, 2009)

I know there is a lot of threads with overheating/overhauling the cooling system of the 98 528 (e39) but I have multiple issues.

I have replaced; radiator, water pump, overflow, fan clutch, and thermostat & housing (twice). All 6-18 months ago.

When I run the A/C at idle, the water temperature spikes, once underway the temp returns to normal. The auxillary fan works but it doesn't seem to turn on HIGH.

Now when I start the car in the morning (65F), the temp gauge fluctuates between normal and high. This morning it spiked to the red so I turned off the engine. After a few minutes the temp returned and I started the car and drove 1/2 mile before is went to red again. Turned off car and waited a few minutes for temp to return. Then I drove with no more problems.

Is the issue with the auxillary fan, thermostat, air pockets, or temp sensor?

Please help one more time!


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## Fast Bob (Jun 4, 2004)

Always check the basics first....bleed the system, you might have an air bubble in there....


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## pde39 (Jun 27, 2009)

I will try that tonight. 
Thanks.


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## pde39 (Jun 27, 2009)

I bled the cooling system and with the car warm there was some air escaping as I opened the bleeder screw. I then added a considerable amount of water/coolant. I hope this works.


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## synenergy52 (Apr 10, 2008)

Check the E39 forum and check CN90's posts. He's a cooling guru. I've done the systems on BMWs as well. Complete cooling overhauls. Make sure the front of the car is raised when you are bleeding your system. When you have a steady smooth stream of water with no bubbles, you're done bleeding. I'd wait 1 or 2 minutes in between opening the bleed screw to give the system a chance to pressurize. Make sure your heater is turned on full blast as well. Keep a constant eye on the temp gauge.


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## synenergy52 (Apr 10, 2008)

Also AFAIK the Aux fan shouldn't turn on HIGH unless the primary fan (belt driven) isn't cooling the car enough.

You probably just have air pockets. Next time it overheats, feel the inlet and outlet coolant hoses out of the engine block. BOTH should be warm/hot. If one is cold, water isn't flowing


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## pde39 (Jun 27, 2009)

Once I bled the air out of the cooling system the car has not overheated. I think that was the problem. Thanks.


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## adischino (Apr 12, 2007)

Same thing here, I just replaced the fan clutch and aux fan and I'm still getting gauge readings higher than the 12 o'clock position, which go away when you start to drive. Fan clutch was bad after all, aux fan was frozen. Now they've both been replaced, did the rad/wpump/tstat and tstat housing about 2 yrs ago. 

Gonna try and bleed her tomorrow, funny thing is now when I put the heat on full blast I get lukewarm heat at best. Anyone think this sounds like a stuck closed tstat? One other thing to mention is the car doesn't get driven frequently, and the last time I did a flush must have been when the dealer did the radiator 2 years ago. No loss of coolant, thoughts anyone?


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## Fast Bob (Jun 4, 2004)

adischino said:


> Same thing here, I just replaced the fan clutch and aux fan and I'm still getting gauge readings higher than the 12 o'clock position, which go away when you start to drive. Fan clutch was bad after all, aux fan was frozen. Now they've both been replaced, did the rad/wpump/tstat and tstat housing about 2 yrs ago.
> 
> Gonna try and bleed her tomorrow, funny thing is now when I put the heat on full blast I get lukewarm heat at best. Anyone think this sounds like a stuck closed tstat? One other thing to mention is the car doesn't get driven frequently, and the last time I did a flush must have been when the dealer did the radiator 2 years ago. No loss of coolant, thoughts anyone?


These days, most `stats fail in the "open" position (thankfully), rather than closed....try bleeding it once or twice and see what happens.


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