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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 07-30-2011, 10:17 AM
entropy4 entropy4 is offline
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Yet another Z4 Overheat question

Hi all, couldn't quite find anything that precisely matched my symptoms, so I was wondering if anyone might be able to help me troubleshoot.

I have a 2003 2.5 Z4 ~110k. It recently began overheating. This does not occur at highway speeds, only while idling. The odd thing is if it begins to overheat while idling i can rev to ~3000 rpm and the engine temp drops back to the middle. I've only really noticed the problem while the AC is on. Unfortunately it's averaging 100 degrees outside right now When turning on either AC or Heat the electric fan does come on, but if I turn on the AC, let the thermometer climb and then turn of the AC, the fan turns off too.

Kinda stuck here and hoping someone has some suggestions before I start randomly buying expensive cooling system parts.

FYI coolant system does not appear to be leaking and was bled when I replaced the expansion tank about a year ago.

Thanks in advance!
Corey
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  #2  
Old 07-31-2011, 03:43 AM
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Pinecone Pinecone is offline
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Sounds like the electric fan is not working.

The electric fan should run whenever the AC is running.
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  #3  
Old 07-31-2011, 05:50 AM
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If it cools down when you rev the engine, it sounds as if the water pump isn't fully working. If it were the fan, revving the engine would not have any impact.
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  #4  
Old 07-31-2011, 10:21 AM
entropy4 entropy4 is offline
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Brilliant, I'll try replacing the WP later tonight.

Thanks for the idea!
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  #5  
Old 08-01-2011, 05:57 AM
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Pinecone Pinecone is offline
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There are two fans. An electric fan and one driven off the engine.

When you rev the engine, the engine fan moves fast enough to actually move air through the radiator. At idle, the electric fan assists if the temps get up.

Check the electric fan before you change the water pump.
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  #6  
Old 08-01-2011, 06:28 AM
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Quote:
Originally Posted by Pinecone View Post
There are two fans. An electric fan and one driven off the engine.

When you rev the engine, the engine fan moves fast enough to actually move air through the radiator. At idle, the electric fan assists if the temps get up.

Check the electric fan before you change the water pump.
My '03 3.0 does not have two fans, only an electric fan.
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  #7  
Old 08-01-2011, 06:28 AM
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Ron Stygar Ron Stygar is offline
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Quote:
Originally Posted by Pinecone View Post
There are two fans. An electric fan and one driven off the engine.

When you rev the engine, the engine fan moves fast enough to actually move air through the radiator. At idle, the electric fan assists if the temps get up.

Check the electric fan before you change the water pump.
No fan?
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  #8  
Old 08-01-2011, 07:35 AM
entropy4 entropy4 is offline
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Just looking at my motor, there is one large electric fan directly in the center of the radiator, I don't see a belt driven fan. I would very much prefer it to be a fan issue seing as how replacing the water pump apparently requires me to move the engine.
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  #9  
Old 08-09-2011, 08:56 AM
entropy4 entropy4 is offline
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Just an update, replaced the water pump and the thermostat for good measure (It does suck that you have to move the engine to pull out the pump).

Needle's been hovering in the middle for two days now, keeping my fingers crossed!

Thanks for your input everyone!
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  #10  
Old 08-09-2011, 07:06 PM
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When this happened to my Audi TT a few years ago it was the electric fan that had stopped working. Your symptoms also indicate a possible water pump issue which you have replaced so good luck!

To check for the fan, it should turn on automatically on a hot idling engine w/o the AC actually being on to regulate the temp by moving air. I don't know what the trigger temp is for BMWs though.
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  #11  
Old 08-13-2014, 05:30 AM
Isaiah73 Isaiah73 is offline
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Overheated z4 when idled

Quote:
Originally Posted by entropy4 View Post
Hi all, couldn't quite find anything that precisely matched my symptoms, so I was wondering if anyone might be able to help me troubleshoot.

I have a 2003 2.5 Z4 ~110k. It recently began overheating. This does not occur at highway speeds, only while idling. The odd thing is if it begins to overheat while idling i can rev to ~3000 rpm and the engine temp drops back to the middle. I've only really noticed the problem while the AC is on. Unfortunately it's averaging 100 degrees outside right now When turning on either AC or Heat the electric fan does come on, but if I turn on the AC, let the thermometer climb and then turn of the AC, the fan turns off too.

Kinda stuck here and hoping someone has some suggestions before I start randomly buying expensive cooling system parts.

FYI coolant system does not appear to be leaking and was bled when I replaced the expansion tank about a year ago.

Thanks in advance!
Corey

I have the same problem even after water pump and thermosated along with pipes and water resovoir was replaced.

Anyone have any ideas what else could be going wrong?
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  #12  
Old 08-13-2014, 05:31 AM
Isaiah73 Isaiah73 is offline
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I have the same problem even after water pump and thermosated along with pipes and water resvoir was replaced.

Anyone have any ideas what else could be going wrong?

I did read that the over heat sensor does need to be reset is that another option?
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  #13  
Old 08-13-2014, 04:13 PM
pokeybritches pokeybritches is offline
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Did you bleed the air out of the system?
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  #14  
Old 08-13-2014, 05:33 PM
Isaiah73 Isaiah73 is offline
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Yes I did bleed the water coolant but not sure about reset the sensor, is that something I can do or do I need a pro?
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  #15  
Old 08-13-2014, 06:29 PM
pokeybritches pokeybritches is offline
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Just to make sure we're talking about the same thing, you purged the air by cracking the vent near the radiator cap as the car was running but cold?

The coolant temp sensor shouldn't be too hard to replace, IIRC.
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  #16  
Old 08-14-2014, 05:03 AM
kalali kalali is offline
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You should also verify the overheat using a temp gun. Also keep in mind engine overheat could potentially damage the cylinder head if it is not addressed quickly.
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  #17  
Old 08-15-2014, 08:13 AM
Isaiah73 Isaiah73 is offline
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Yes the coolant was blended the only two things not replace was sensor and fan..
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  #18  
Old 08-15-2014, 08:19 AM
pokeybritches pokeybritches is offline
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Quote:
Originally Posted by Isaiah73 View Post
Yes the coolant was blended the only two things not replace was sensor and fan..
The coolant being blended or replaced has nothing to do with purging the air from the system...
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  #19  
Old 08-15-2014, 02:35 PM
Isaiah73 Isaiah73 is offline
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Yes the air was purge and took it to be looked at and it turns out it was some bad wiring. Fingers crossed... thanks guys for the help.
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