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Thread: Please help diagnose ...

  1. #1
    Join Date
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    Question Please help diagnose ...

    Greetings to the forum!

    Did not find specific answers searching around, please help me diagnose the trouble ..

    1996 E38 740iL

    Water pump and thermostat were replaced few thousand miles ago. Car had a defective fan that broke the old water pump. Car was running great after the replacement.

    First thing I noticed around 2-3 weeks ago was that the coolant was vanishing somewhere .. no visible leaks around the water pump, nothing under the car. Had to start adding around 1/2 pint in a week or so, sometimes bit more.

    Suddenly the exhaust started smelling like gasoline a LOT, MPG went down 3 units.

    Checked the codes, looked like Oxygen sensor @ Bank 2. I replaced the O2 sensor few days ago, MPG stayed low ... next thing, a PENDING code " P0116 Engine Coolant Temperature Circuit Range/Performance problem" came up.

    Today the PENDING on P0116 changed to FAULT.

    MPG is still too low. Smell of gasoline is less than it was before O2 sensor change but is still there ...

    EDIT: After the PENDING code turned to FAULT, the engine temp gauge started showing wrong. It was always at 1/2 when engine warmed up, now it stays at 1/4. I took out and plugged in again the connector from the sensor in the radiator and the gauge went close to the position it should be. Could it be that the radiatior sensor is causing low MPG ?

    I have a shi**y code reader and nothing better nearby at the moment, please share some ideas where to start looking for the problem ...

    Thank You ahead!
    Last edited by vonpakkas; 12-10-2018 at 07:07 PM.

  2. #2
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    a bad thermostat causing a clod engine will reduce MPG
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  3. #3
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    Learning every day! Thanks for the reply! I assume the thermostat is OK, just replaced with OEM part. Messing with the radiator temperature sensor plug fixed the gauge for a short while ... could be that this is it ... new is on the way! Will post update after replacement!

  4. #4
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    Cooling system might have air pockets or sensor starting to fail. Try to compare temperature readings in the dashboard or scanner live data during engine warm up with with actual temperature. You can switch you dashboard to digital reading using service mode.

    - - - Updated - - -

    Engine temp sensor is not in the radiator. It is in thermostat housing on M62 and behind intake manifold on M60.

  5. #5
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    Hmmmm got it ... Water pump and thermostat were recently replaced, which does not mean that the new one couldnt have broken down ... is there a chance that there is a bubble in the system causing this ? Coolant is slowly vanishing from the system, maybe it sucked in some air and this is messing the thermostat up ?

    Just thinking out loud before buyng new sensor!

    Though as I have the fault code on the system, it probably cannot be just the air bubble in the system ?
    Last edited by vonpakkas; 12-11-2018 at 01:45 PM.

  6. #6
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    Quote Originally Posted by vonpakkas View Post
    Hmmmm got it ... Water pump and thermostat were recently replaced, which does not mean that the new one couldnt have broken down ... is there a chance that there is a bubble in the system causing this ? Coolant is slowly vanishing from the system, maybe it sucked in some air and this is messing the thermostat up ?

    Just thinking out loud before buyng new sensor!

    Though as I have the fault code on the system, it probably cannot be just the air bubble in the system ?
    I don't think the new thermostat is faulty. If you have a code, most likely sensor has some problem, maybe intermittent. This is why you should check the temp values with scanner. For example, if the engine is cold and temperature outside is 20 degrees than coolant temperature should be roughly the same. If it shows 40 degrees, than you know the readings are incorrect. Or if during warm up temperature jumps from 20 to 60 in one second this is again impossible.

  7. #7
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    I opened up the dashboard diagnostics and got some temperature readings from there ...

    First drive, with temp gauge showing engine fully warmed up, 15 minutes drive, KTMP reading did not go above 79C.
    Second drive, around half hour on highway, gauge stayd at 11 oclock never reaching the center, KTMP reading 69C max.

    Otherwise, the reading acted normally, temperature went up degree at the time etc.

    Any ideas ?
    Last edited by vonpakkas; 12-11-2018 at 11:43 PM.

  8. #8
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    Your thermostat is not fully closing or installed incorrectly - that's about it for possibilities unless the temperature sensor is not reading the temperature correctly.....
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  9. #9
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    Quote Originally Posted by Timm View Post
    Your thermostat is not fully closing or installed incorrectly - that's about it for possibilities unless the temperature sensor is not reading the temperature correctly.....
    Hmmm, it was installed 3 months ago, the engine warmed up fast until just short while ago. New part on not, I have to agree that is has to be broken. Or could it be that the incorrect installment just did not affect it at first but started doing it in few months ? Seems unlikely as the installment is quite straight forward ...

    Ironic situation, bought a good OEM water pump and thermostat just for the reason that I would not have to replace it on this car again
    Last edited by vonpakkas; 12-12-2018 at 10:02 AM.

  10. #10
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    I'd say it's more likely the thermostat is defective in that case. Wrong installation should have been obvious right away.

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