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Thread: Thermostat

  1. #1
    Join Date
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    Thermostat

    Hey everyone!
    I have been reading about the thermostat mod, or should I just say replacement. Seems like replacing the OEM with a newer and lower temp rating might be good for the life of the motor.
    Doesn't look too hard to replace, just wanted to know if anyone has done this already, and if so were there any surprises. I understand I will loose some coolant, and have to replace it... is that
    a simple matter of refilling the tank after the job is done.
    The original is rated at 105C, but the replacement is 90C.
    Timm, if your out there, any thoughts?
    Thanks guys for any information you may provide...!

  2. #2
    Join Date
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    The original thermostat is a temperature-mapped device, a mechanical 108C thermostat with a built-in heater that allows the thermostat to be opened down to 85C - more information (from the M62 specs - but the N62 uses the same thermostat):

    https://www.meeknet.co.uk/E38/M62%20...ls.pdf#page=10

    It is used by the DME (engine computer) to adjust the coolant temperature as it enters the engine - hotter for part-load driving (better MPG), and cooler for full load (better power). If it has been fiddled with you will probably get an error code, but I doubt if this will illuminate the check-engine light on the dash.

    The temperature as seen from an unlocked dash display is measured at the outlet from the engine so this will be higher than the thermostat chamber temperature - usually 10C hotter.

    As far as I know, the thermostat supplied is the standard thermostat, but fiddled with, sometimes by squashing the wax chamber, sometimes by fiddling with the spring tension - neither of which is that accurate. But, if they do reduce the low-load temperature then I'm all for it!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    Many Thanks Timm. I am thinking the lower temperature will be good for the motor in general. Would you agree that doing this would also lower the oil temp a small amount, as well...?
    I was reading your coolant system problems, but could not read the link concerning bleeding after working on the system. Is there a set procedure to accomplish that?
    Additionally, I noticed my car has a separate cooler located at the bottom of the radiator, its the same width as the radiator, but only about 3" tall... is this an oil cooler?
    Since installing the Avin system with the OBD adapter... I really appreciate the extra gages one can select. I am not so much interested in the acceleration features, just having coolant temp,
    and instant mpg are valuable. What is does not have is oil pressure, which would have been nice.

  4. #4
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    OK, a quick update. Got the new thermostat installed, lost about a gallon of coolant in the process, but bought more of the blue stuff (bmw). So no problem there. I thought I had the hose connected from the radiator to the thermostat, but it must have been not completely seated.... ended up with a slight leak during the bleeding, and initial drive. The coolant temp remained at 90 to 93 C during the drive, which was my goal.
    Hose is now reseated, and more coolant added.... waiting to go out and drive again, hopefully no more leaks.
    One thing that did happen, the little plunger that goes up and down in the coolant tank broke, actually it was very soft, and about to start disintegrating. Does anybody know if you can replace the plunger, or do you need to replace the coolant expansion tank?
    Since my car did not have a bleed screw, I look everywhere, I used the upper hose squeezing method to purge out the air bubbles.

    - - - Updated - - -

    One more thing.... "TIMM" thanks for your help and guidance, your the man!

  5. #5
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    2001 525it
    Replace the expansion tank and hoses, its old.

  6. #6
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    Yes, you are probably right. I am putting that on my to do list.
    Anyone done this...? Timm?
    Looks simple enough, at least I hope so!

  7. #7
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    UPDATE! Just finished the expansion tank replacement. I siphoned out the coolant first, then removed the hoses, then the tank. Worked out quite well, and no coolant spill.
    Have not done much driving lately, but from what I notice so far... the engine oil temp is running cooler, along with the coolant temp. So far,very pleased with everything.

  8. #8
    Join Date
    Aug 2019
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    Seattle
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    1997 BMW E39 528i
    Hello, did you replace thermostat by "ready solution" usually around $200, or found one that fit into caddy? If fit into caddy, what part number it have? Thank you.

  9. #9
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    Wow, funny how things happen. Yesterday I finally tossed the old thermostat in the trash.... and your post comes today. I do not remember the company it came from. It did come in a new housing, so it was a simple R&R. The new one runs between 90 to 94 C, vs the old one that was 105 to 107. Also, the oil temp seems to run cooler, the needle never goes to the mid point on the gage now.

  10. #10
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    Apr 2018
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    Wilkes Barre PA
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    2009 BMW 650i
    I found a hidden menu which you guys might know about. Press and hold the odometer reset until the VIN comes up. It showes you RPMs digitally and it also shows ambient air temp and coolant temp. I can’t get heat at high speeds. I froze my ass off driving home from DC thanks

  11. #11
    Join Date
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    Montreal Canada
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    BMW 645 E64 2005
    Quote Originally Posted by dhlairbus View Post
    Hey everyone!
    I have been reading about the thermostat mod, or should I just say replacement. Seems like replacing the OEM with a newer and lower temp rating might be good for the life of the motor.
    Doesn't look too hard to replace, just wanted to know if anyone has done this already, and if so were there any surprises. I understand I will loose some coolant, and have to replace it... is that
    a simple matter of refilling the tank after the job is done.
    The original is rated at 105C, but the replacement is 90C.
    Timm, if your out there, any thoughts?
    Thanks guys for any information you may provide...!
    hello there,
    one thing i can advise you is not to use the logic7, way overprice and its not accurate. they claim it opens at 95 but really opens at 103. i have even spoken to other people who have used it and were quite disappointed. finally what i did was use the original thermostat and heat up the coil with a torch, that would weaken the spring. now the thermostat opens at 93 and my temp does not go higher than 95. its gamble but worked for me and at least its cooler that what it was. good luck

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