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E85 / E86 Z4 (2003-2008)
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Old 08-07-2012, 03:01 PM
'04Z4 Texas '04Z4 Texas is offline
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Mein Auto: BMW '04 Z4
overheating '04 Z4

My '04 Z4 is overheating. I took it to a dealer and they replaced the sensor sending unit. The car still overheats. Fans are working. Coolant is full. Any suggestions? I also realized the temperature gauge is actually more like a switch than a gauge. It jumps in increments when the car gets hot. (buffered?) anyone have experience with this? Car only has 60k on it and has been well maintained. I don't want to take a shotgun approach to the issue and start replacing a bunch of parts needlessly.
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Old 08-07-2012, 03:30 PM
wifesauto wifesauto is offline
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many many things to check. thermostat,radiator plugged[inside /outside] ,water pump [flow] hose flattening. head gasket
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Old 08-07-2012, 04:32 PM
ZEEBOY ZEEBOY is offline
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Mein Auto: 2001 Z3 Coupe
Jumping in increments often means air in the coolant system. But, that does not just happen for no reason...usually the result of improper filling after waterpump or thermostat replacement...
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Old 08-07-2012, 05:17 PM
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acoste acoste is online now
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The position of the gauge is not linear to the measured temperature. It stays in the middle for a wide range, something like 80-115 Celsius and then rapidly moves to the right.
Watch the real temperature value
(I can do that on my model when I unlock the instrument panel by pushing the reset button in a specific way)
Does the overheating happen at traffic lights, in the city or on the highways?

Sent from my ADR6350 using Bimmer App
2010 BMW 550i MT
2003 BMW 325i @195k and counting
1998 BMW 528i MT @ 231k //sold
1997 Saab 9000 //sold
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Old 08-07-2012, 06:32 PM
chickdr chickdr is offline
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How many miles on the car? It may just need a cooling system overhaul? New radiator, hoses, water pump, thermostat. Newer BMW's supposedly need the systems done every 50-100k.
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Old 08-08-2012, 03:18 AM
Mikey48 Mikey48 is offline
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Mein Auto: BMW Z4 3.0
I agree with ZEEBOY. If your gauge is jumping around there could be air in your cooling system. Is your water at the right level in the rad ? The stick you see rise after you remove the rad cap should rise to the 2nd ball on the stick to the rad inlet no further ! Also double check your hoses. My 2004 Z4 3.0i had a hose go bad and started leaking after I would turn the car off. It turned out to be the top rad hose was bad.I replaced it flushed my cooling system making sure to get all the air out of the cooling system. You have to remove the shroud at the top of the rad to get to the bleeder screw. Some cars will burp themselfs if you start the car when it is cold and let it idle with the rad cap off and let it idle up to temperature. Keeping a close eye on your temp gauge. DO NOT drive your car if it is running hot ! You will kill your car !!! This is where I would start. Good luck !
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Old 08-08-2012, 03:35 AM
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crewdog843 crewdog843 is offline
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So the dealer replaced the sending unit without testing the car to see if would overheat afterwards...shoddy workmanship. You may have to bleed the system as you may have air trapped in it. Don't forget to put the heating control for the cabin to full hot, and park on a slight incline. BTW: What caused it to start overheating in the first place?

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Old 08-08-2012, 04:08 AM
brock5ga brock5ga is offline
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Location: Monroe, GA
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Mein Auto: Z4
BMW has had problems with the plastic impellers on the water pumps. There are aftermarket versions available with metal impellers. Check in order 1) Air in system 2) Water pump impeller ( I usually use the small hose to the reservoir to check for flow, but I don't see one on my 03 unless it is under the cover) 3) Blown head gasket (Usually results in pushing water out of system. Should notice visible water loss.) My guess is the water pump.
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