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Thread: Peculiar Coolant Temp Gauge Issue

  1. #1
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    Peculiar Coolant Temp Gauge Issue

    The coolant temperature gauge on my e34 touring is concerning me and I am hoping to get some advice/recommendations from the e34 gurus.

    Specifically, after shutting off the car after a highway drive and restarting it within 15 minutes or so, the coolant temp gauge on the dash moves to the 3/4 mark and then, after the maintenance lights turn off, the needle goes back to its normal 1/2 mark (actually just a hair/cm beyond the 1/2 mark). The gauge stays fixed at the 1/2 mark during all driving conditions and does not overheat or run hotter than normal. This has been happening for quite some time and I would like to learn more about possible causes/issues.

    By way of background, the touring has a new cooling system, including wp, thermo, hoses, etc. that was installed when I purchased the car in 11/2016. I also added new coolant temp and gauge senders under the intake manifold. The radiator was not replaced, but is a Behr model that is less than 2 years old and looks to be in good shape. The temp gauge itself seems to be working properly as evinced by the self test for the dash gauges. I have also bled the system on numerous occasions and am confident that I do not have any (or a significant amount) of air in the system.

    My gut is telling me that it may be a partially sticking thermostat, but other than the "hot start" issue, the thermo seems to be functioning properly. Any thoughts/guidance would be very much appreciated. I can also post a quick video if it would be helpful. Thanks all.
    Last edited by squirrelhill; 06-04-2018 at 11:10 AM.

  2. #2
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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  3. #3
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    Thanks for the response. Is there anything I can do to mitigate the heat soak or is it really a non-issue?

  4. #4
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    It's a non issue BUT I'm pretty sure you could program the heater to run after shut down via the OBC operating the aux coolant pump. That would mitigate the heat soak by circulating coolant through the heater core. Expect a hot cabin if you get in shortly after.
    If it really bothers you the pump could be connected to a timer to run automatically after shut down. I think the old MB W123s did that, just not through the heater.
    Last edited by ross1; 06-05-2018 at 12:24 PM.

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  5. #5
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    Thanks Ross. I am glad that the heat soak is not a major issue and I will explore the OBC option. I will post if I discover a viable solution.

  6. #6
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    Its normal. If it bothers you that much instal an electric fan and have it relay off battery and not ignition based.

  7. #7
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    Quote Originally Posted by Hofmeister View Post
    Its normal. If it bothers you that much instal an electric fan and have it relay off battery and not ignition based.
    That's how I have mine set up. Not my own doing but the PO removed the belt/clutch fan and hooked up an electric fan with it's own relay and t/stat straight off the battery.

    With a new rad, engine thermostat and coolant flushed the elctric fan only runs after parking it. My engine temp usually stays on the halfway mark while driving without any fans running anyway.
    I've set the fan's t/stat to only run when above halfway, and the only time it gets hotter than that is after parking as the water pump has stopped. So a few minutes after parking my fan comes on for 5-8 min.

    There doesn't seem a point to it because the pump isn't running, it's just cooling the rad until the engine thermostat shuts so there's no real benefit. But it's installed and controlled as the PO set it up and if that's the only time my fan runs then I know the temp setpoint is good because that means if in extreme conditions where the temp gets over halfway when driving the fan is set to come on at those temps.
    Last edited by fo3; 06-11-2018 at 07:24 AM.

  8. #8
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    Thanks all -- the e-fan modification is certainly on my radar.

  9. #9
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    Just about finished wiring my setup, and like fo3, I have it running of battery so it will work no matter what. That being said, I have never noticed the heat soak on my 525, you may want to do a coolant flush and reattach your aux pump.


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