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Registered User
Join Date: May 2005
Posts: 71
BMW Roundel '86 325es cooling

this just rose this morning on the way to the last 2 months i've done complete maintainance on my car, including the water pump and thermostat (75 deg celcius). i look down at my temperature guage while at a stop light, and it's reading 2 marks above normal (one notch above half). it normally sits right between half and the first notch. it would gradually creep up, then cool down when the car was moving, but never below the halfway mark. then at stoplights, creep up again.

i understand it was never overheating, but still was not functioning properly. i'm thinking the thermostat could have been stuck, or not opening all the way, but i just replaced it. could have been a bum part i guess, but it was a "gutes deutsches" replacement, so i figured it would last. i have plenty of coolant. no apparrent leaks, from what i see. no steam. no coolant in oil. hopefully just thermostat................

any ideas? clueless in miami..... thanks
Old 05-04-2005, 04:36 AM
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Registered User
Join Date: May 2003
Location: Kernersville, North Carolina
Posts: 13
Did you bleed the system?
Old 05-07-2005, 09:01 PM
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Join Date: May 2005
Posts: 71

yes, i did bleed the system, and added some coolant. guage worked fine, thermostat opened at correct temperature, get home from work, park my car and 2 hours later there's a puddle of coolant below my beloved bimmer.

trace it down to the water pump gasket, PITA......does the water pumps on bimmers have a weeper hole like some domestic cars do? buddy of mine said the pumps (domestic) have a weeper hole that work like a pressure-regulated bypass when an internal seal goes bad, but the pump i used was so simple i don't think there was an internal i correct?

i used the stock paper gasket in concert with ultra blue gasket maker to keep it from leaking(2 mos ago).....i know i couldn't have added too much coolant, cause it would have come out the overflow tank. also do not see any leakage from the head, or coolant in oil, etc.....

Old 05-08-2005, 09:38 AM
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Join Date: Oct 2004
Posts: 14
I would be interested to know what you find on this one. I have similar symptoms on my 89 except that mine normally will run just below the center and creep up. I am the original owner and it used to be rock steady in the center.

Old 05-23-2005, 05:12 PM
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Location: Poquson, VA
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In my experience it has been the viscous fan clutch that creates a temperature rise in traffic and a cool down at speed. Every time I had this problem, I changed the fan clutch and the problem went away.
Old 06-08-2005, 06:05 PM
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Junior Member
Join Date: Jan 2005
Posts: 5
Anyone find a solution to this one. I have the same problem in my car.
I've replaced :

Fan clutch twice
Thermostat twice
water pump

I suspected the gauge but the aux fan comes on when the gauge is at three
quarter.....I think this is right. Anyone know if there is a backup switch on the
aux fan that keys off the temp gauge sender???? Or just the one mechanical?
Old 07-29-2005, 09:09 AM
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BMW cooling systems are the weakest point of the egine. The system has a tendency to trap air bubbles which create pockets of heat and prevent cooling. Before troubleshooting any cooling problem, I tell people to bleed, bleed, bleed again and again. Bleed, then run the car, then bleed again, etc.

After that, you can start measuring temps at the radiator and hoses (infrared thremometer, $60) to see if your thermostat is opening up all the way, and to see if your water pump is pumping properly.

Also, if you forget to replace the o-rings around the water pump and/or the thermostat, then you will not have efficient cooling (some people forget these).

Wayne R. Dempsey, Founder, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997
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Old 07-29-2005, 11:59 AM
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