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    Member No: 97719 ncamie is an unknown quantity at this point ncamie's Avatar
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    Thermostat Sensors

    Hello All,
    I have a 1988 535is with some cooling problems I'm trying to solve. I'd like to know which are the names of the sensors on the thermostat as you look at it from the front of the car and the sensors from left to right. I have included a link to a picture here http://picasaweb.google.com/Norman.Camamile/MyPictures/photo#5155013992619175970

    Please list the sensors as they appear on top left, top center, top right, and bottom right. I have attempted to use the picture on the REALOEM website but its a bit confusing. Thanks, Norm


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    I think the other board has some pictures at the

    top of the page. bimmerb oard dot com

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    Re: Thermostat Sensors

    ECU temp sensor
    Thermo time switch (cold start valve)
    Gauge sender

    Green vac valve (purge valve?)

    If you have a lot of that RTV blue sealant (engine to thermo housing in picture) on more things like the water pump etc, that stuff may be clogging up the system.

    What are the symptoms of your cooling problems?Steve B
    4/85 e23 735i (summer/fall use)
    1/88 e32 735i (winter/spring use)
    6/88 e32 735iL (long term project)

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    Re: Thermostat Sensors

    Hi,
    Well there are several symptoms. Firstly, my coolant level LED light illuminates (the one up by the rear view mirror). This happens about 3 to 5 minutes after I start and drive the car. I have checked the coolant level and there are no leaks though the level is a little bit higher (maybe one fingernail width) than the arrow mark on the tank.

    Secondly, on the same drive if you observe the temperature guage in the instrument cluster, as we drive the engine starts warming up normally but the temperature needle won't stop at the normal 12 o'clock position, it continues to go on to just below redline and on rare occasion redline. Continuing the same drive, the needle doesn't steady on one reading, instead it behaves sort of erratically. It may vary slightly (not enough to ease my overheating worries) as I apply and remove the gas pedal, brake pedal, and other electrical components. Occasionally and without input from me the temperature needle might bounce back to the middle where it should be, but immediately starts creeping back up toward red.

    So far I haven't had any boiling over, pinging, power loss, or other adverse side effects (that I know of). The car drives great but I am really worried about this.

    In trying to remedy both problems I have bought a new bavauto coolant level sensor (the one with the bob/float) but no changes there. Previous to this new sensor I jumped the terminals and there was never a low fluid indication, but now with the sensor it just won't go away and tells of a bad sensor. Is there a way to test the sensor?

    Additionally I removed the radiator and back flushed it. Seems good but couldn't look inside. I removed the water pump; it looks good. Removed and "cook tested" the thermostat; it opened and closed fine at the right temperatures. I re-installed it arrow up and spring assembly facing rear and out of sight.

    I bled the coolant system of air with the cabin heater wide open/hot and the engine running on a steep incline engine facing uphill. Is that all the is to bleeding?

    I don't know of a way to test the radiator cap but the hoses are warm/hot, and pressurised/firm when the engine is hot. I assume this is a good cap.

    I found out that the fan clutch is freewheeling and I need a new one; it won't lock up when the engine is hot. I'm not worried about fixing this yet though because 99% of my driving is on the highway at highway speeds at night and it is really cold here where I am at. The problems my car is having occur during this highway driving.

    I have checked and noted down the resistance readings of the three sensors on the thermostat housing when they are cold, warm, and hot but I don't have my Bentley here and accesible to know what they should be reading.

    Sorry for the extra long post but hopefully I have been descriptive enough to give you guys an idea of what is going on.

    Norm
    1988 535is

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    Re: I think the other board has some pictures at the

    Thanks! I didn't know of that board. I'll check it out.

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    Check your ground straps-

    when I had my 86 535i, it would do the same thing with the gauge. The longer I had the motor running the higher the gauge would read. If I turned on an electrical accessory, the gauge would respond and move around.
    I found that the meter readings didn't match when I measure between the battery terminals and the alternator. I added another ground strap from the battery to the intake manifold and it cleared up the gauge problem. I never really had a chance to troubleshoot correctly and see where the problm actually was, but the extra strap fixed the temp gauage.
    In addition, I also had a no start situation, which required me to add another ground from the back of the valve cover to the passenger side upper strut mount, so check that strap too. You might as well check and clean all of your straps and connections: battery/body, valve cover/firewall, passenger side motor mount/body, alternator (grounds through the bracket on yours), battery terminals.

    If you jump the expansion tank plug and the light goes off, then the sensor is bad. If you jump it and the light is still there, then you will have to troubleshoot some more (maybe the check panel is bad??).

    Get a new clutch as soon as possible, it only takes one traffic jam or snow storm to force you to have to idle the car or creep along-especially with the unknown temp gauge readings.Steve B
    4/85 e23 735i (summer/fall use)
    1/88 e32 735i (winter/spring use)
    6/88 e32 735iL (long term project)

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