Coolant level sensor too sensitive?

  • Hello dear community,

    After a long search, I (Daniel, 41) am finally the proud owner of a 986, year 97 with 200,000 km but in a very good and well-kept condition. The first 500km home were also without problems except for one small thing. After a few kilometers the coolant level warning light started to flash. However, the coolant level has not changed by a millimeter and is still as it was at the beginning - full to the brim. After I unplugged the sensor, the flashing was also gone. Today I took a closer look and removed the sensor... No flashing. Sensor reinstalled... flashing again. Then I thought that maybe the float was stuck, but it was also moving perfectly. As a final test, I only installed the sensor "halfway" and did not lock it. The flashing was off and came on as soon as I pushed the float down with a rod. Could it be that the sensor is suddenly more sensitive than before? I noticed that the sensor can be moved in the expansion tank despite being locked🤔, can anyone confirm that this is normal? The expansion tank and sensor are only 1.5 years old. Perhaps someone has already had the same problem and can tell me whether it makes sense to replace the sensor or whether it might be due to something else.

    Lg

    Daniel

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  • The "sensor" is just a lot of plastic with a reed switch, a switch that reacts to a magnet. The magnet is in the float. The reed switch itself cannot move, the sheet metal tongue is sealed in a glass bulb.

    Is the float still floating at the top or is it already a submarine? It is conceivable that the float is not completely sealed and is therefore sinking further and further, causing the sensor to respond.

    Greetings

    This post has been automatically translated.

    Nach 320'000 Spiegeleiern kann die Kantine nicht so schlecht gewesen sein!
    Harm Lagaay

    PS: Ich heisse nicht Greetz k:thinking:

  • Thanks for your input. I would say the float is at the upper stop, but the coolant goes 1 to 2 cm above the float. I've only tried pushing it down so far. I'll get a wire and try pulling it up. Let's see what happens😉. The sensor was quite loose in the housing, maybe the glass body was damaged🤔

    Greetings

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  • The sensor should look like this, straight and unbent. The reed switch itself is a normally closed contact, i.e. without a magnet nearby it is closed and the current flows. If a magnet comes to the sensor, one contact bends and the circuit is open.

    How does the plug connection of the sensor face the expansion vessel? I don't know whether the sensor can be installed upside down by 180°, but you could check that.

    Greetings

    This post has been automatically translated.

    Nach 320'000 Spiegeleiern kann die Kantine nicht so schlecht gewesen sein!
    Harm Lagaay

    PS: Ich heisse nicht Greetz k:thinking:

  • Are you sure that it is a normally closed contact?

    If no sensor is connected, the flashing is gone. I could also swear that the contacts did not touch without a magnet🤔

    When locked, the plug looks approx. 45° to the bottom left


    Greetings

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  • Aaalllso, new sensor is installed, same problem. The float is definitely floating right at the top at the stop🤔.


    What else I noticed... The dashboard has a funny wobble, if I move it directly after turning the key then exactly this light goes out or flickers. After the "self-check time" is over, the wobble also seems to be gone, at least I can't "turn off" the flashing. Could this be connected somehow?

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  • Check the plugs on the back of the speedometer unit. These are locked plugs, but perhaps something is "bent" there. The alternative is then the wiring harness...

    Greetings

    This post has been automatically translated.

    Nach 320'000 Spiegeleiern kann die Kantine nicht so schlecht gewesen sein!
    Harm Lagaay

    PS: Ich heisse nicht Greetz k:thinking:

  • Then I'll give it a try. However, it is still the case that it does not flash when the sensor is outside the tank, as soon as I insert it the display flashes. If I only insert it "halfway", i.e. I don't let it click into place but leave it on the floor of the vehicle, it doesn't flash or only flashes when I press the float down. I'm thinking about building my own sensor that is a bit shorter, that should solve my problem

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  • Pilot69 could you perhaps take a photo of your float when you get the chance, I have the feeling that the installed tank is not compatible with the original sensor because the float sits too low in the uppermost position.

    That would be super helpful to check this

    Greetings

    Daniel

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  • I'm currently on the road in Italy on various race tracks...

    Greetings

    This post has been automatically translated.

    Nach 320'000 Spiegeleiern kann die Kantine nicht so schlecht gewesen sein!
    Harm Lagaay

    PS: Ich heisse nicht Greetz k:thinking: