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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 12-24-2014, 12:24 AM
emann117 emann117 is offline
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Possible thermostat going out?

Hello everyone. So today has been a day and a half. Started out this morning running some errands and noticed in the bank line, that my car was overheating. I quickly pulled out of line and drove into a parking space. Then I noticed as I was driving into the space, the temp had gone down. And went back to normal. I stayed there for a while to let it cool. And then it happened while driving down the road. And I pressed on the gas more and the temp went down again. What could this be?!? Please help!!!!

1998 528i
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  #2  
Old 12-24-2014, 03:34 AM
AH673000 AH673000 is offline
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That's a good bet.... Either that or a water pump..... I would plan on doing both if they are original along with the thermostat housing.
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  #3  
Old 12-24-2014, 05:53 AM
pudl pudl is online now
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A faulty E39 thermostat would cause low temperatures not overheating.
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Old 12-24-2014, 06:16 AM
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ztom ztom is offline
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Quote:
Originally Posted by AH673000 View Post
That's a good bet.... Either that or a water pump..... I would plan on doing both if they are original along with the thermostat housing.
Probably neither IMHO. More likely to be low on fluid, fan clutch (do newspaper test) and/or combustion gas getting into system. Checking the hose temp for radiator fluid from radiator to engine could give good diagnostic info.
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Old 12-24-2014, 07:36 AM
cn90 cn90 is offline
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Tow the car home.
Then sit in front of a computer and start searching "cooling overhaul" before you regret big time.
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  #6  
Old 12-24-2014, 08:54 AM
bmw540san bmw540san is offline
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I'd start with the question to OP. Have you done anything to cooling system yet or you simply don't know? If former, you better do a complete cooling overhaul if you're planning to keep the car.
Also, that symptom could be as simple as sticking thermostat and as complex as blown head gasket. I'd diagnose it properly first before proceeding any further.

Last edited by bmw540san; 12-24-2014 at 08:59 AM.
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Old 12-24-2014, 11:09 AM
emann117 emann117 is offline
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A new motor was put in the car about a year or so ago and with that came a new cooling system. The pump is working fine. Not sure. It might have just been low. I mean I added quite a bit of fluid. But later on the night after adding the fluid, it started to heat up again, so I hit the gas again and it went down to normal again. And normal for me is shy of 12 o'clock. So like 88 degrees Celsius?
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Old 12-24-2014, 12:16 PM
bmw540san bmw540san is offline
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Quote:
Originally Posted by emann117 View Post
A new motor was put in the car about a year or so ago and with that came a new cooling system. The pump is working fine. Not sure. It might have just been low. I mean I added quite a bit of fluid. But later on the night after adding the fluid, it started to heat up again, so I hit the gas again and it went down to normal again. And normal for me is shy of 12 o'clock. So like 88 degrees Celsius?
Are you 100% sure that cooling system is properly bled? Also, you do know you can unlock your low cluster OBD and check the actual coolant temp (test#7)?
I'm sure you know that coolant temp gauge is buffered and 12 clock needle position can be anything from 75 C to 110 C. It's simply not possible to know the exact temp. without unlocking OBD.

Last edited by bmw540san; 12-24-2014 at 12:19 PM.
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Old 12-24-2014, 12:28 PM
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johnstern johnstern is offline
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+1. You need to bleed the cooling system and make sure it's full IMHO.

http://www.bimmerforums.com/forum/sh...-(Low-and-High)

The thread below has an excellent procedure for leading a 540 in post#2. There is other great info in the thread too.

http://www.bimmerfest.com/forums/sho...d.php?t=514099

Last edited by johnstern; 12-24-2014 at 12:45 PM.
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  #10  
Old 12-24-2014, 08:14 PM
emann117 emann117 is offline
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Quote:
Originally Posted by johnstern View Post
+1. You need to bleed the cooling system and make sure it's full IMHO.

http://www.bimmerforums.com/forum/sh...-(Low-and-High)

The thread below has an excellent procedure for leading a 540 in post#2. There is other great info in the thread too.

http://www.bimmerfest.com/forums/sho...d.php?t=514099

Okay. Thankyou all for the responses. This will sound kinda dumb but I've never bled coolant. How do you do this? I'm 16 and not experienced. But I have done all other work on my car.
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