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Thread: Thermostat

  1. #1
    Join Date
    Nov 2018
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    parrish, fl
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    650i, E350

    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
    Feb 2010
    Location
    Hampshire UK
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    7,077
    My Cars
    99 840ci Sport Indv
    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


    My Current 840ci Sport Individual
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  3. #3
    Join Date
    Nov 2018
    Location
    parrish, fl
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    650i, E350
    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
    Join Date
    Nov 2018
    Location
    parrish, fl
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    My Cars
    650i, E350
    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
    Join Date
    Jan 2016
    Location
    Ca
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    3,167
    My Cars
    2001 525it
    Replace the expansion tank and hoses, its old.

  6. #6
    Join Date
    Nov 2018
    Location
    parrish, fl
    Posts
    50
    My Cars
    650i, E350
    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!

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