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  1. #1
    loach1
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    Temp gauge shot up then down - all OK?

    Twice in the past 3 days my temp gauge has shot up into the red upon starting after being away for 30 minutes or so, then as soon as I get moving it shoots back down again. It's hot in NC this time of year so AC is blowing very loud and I can't determine if aux fan is failing to come on or not. Does this sound familiar to anyone? Usually it is pegged at the midpoint when I'm driving, or stuck in traffic so I'm a bit mistified. If this car boils over and needs ANOTHER tow, it will be history.


  2. #2
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    Have U checked the water level in the expansion (m

    tank? You might be low. Do it when the engine is cold.
    You can get out of the car and see if the fan in front of the radiator is running when the AC is on, it should be.
    The needle should stay in the center even when it is 100 outside, mine does.


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  3. #3
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    Member No: 111493 rajaieq is an unknown quantity at this point rajaieq's Avatar
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    Low on coolant


    If I'm right on this, you're gonna get an earful from me :)

    The temperature gauge is normalized. If the temperature is within a normal range of operation the gauge is artificially set for noon. As soon as the temperature goes outside the range the gauge will show a true representation of the temperature. Thus the gauge will jump back and forth from noon to red hot very quickly.

    Overheating when idle and then cooling down when the car starts moving is a common occurrence. The moving air cools down the radiator. I've had the same situation. The problem is almost always low coolant. The last time I had the problem was when you worked on my car and drained half my coolant on my garage floor. You told me then that I had overfilled coolant. Thank you. :D

    Now, if you fill her up and bleed several times and still find that you're loosing coolant then you need to look for a coolant leak. The most effective approach is to perform a pressure test. I'm not familiar with commercially available products. Of course the TIS calls for a BMW special tool.

    If I'm right on this you'll have to answer my questions and hear me nag about my driveline problem for another year!! ;)

    Meanwhile you need to fill up coolant before you blow your head gasket. I have a gallon of the BMW blue. You donít want to mix in an after market product with the original. As a matter of fact, you need a flush anyway, as I had recently suggested. How about I come over and bring some of the goods. But youíre gonna hear it from me!

    And I donít want to hear it from you about how the auxiliary fan is supposed to come on and resolve an over heating problem due to low coolant!! ;)
    Rajaie
    528i 5sp 06/00

  4. #4
    loach1
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    Coolant appears normal

    The guideline is 'max' with the float level with the top of the threads on the expansion tank when cold. I just checked (quite cold) and the float was level with the bottom of the threads, or 3/4" below max.

    The car keeps cool in traffic in 100deg heat so I think it's more like an electrical gremlin that doesn't turn the fan on or won't because the electrical load is so high (AC fan blasting, etc.). The scenario was the same both times - left the car for 30 minutes after an uneventful stop/start srive in 100deg heat, got back in and started up only to watch the gauge go up, moved 100 yds or so in a parking lot (not fast enough to make anything cool), then temp dropped just as quickly as it went up.

    Rajaie keeps his coolant overfilled - I'm surprised he hasn't blown a gasket! Why does his car overheat if he has 'only' the correct level in the system? What is the weakness here? Pump? Temp sensor for the fan?

  5. #5
    Jim Cash
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    Re: Temp gauge shot up then down - all OK?

    Actually I would expect to see this more often, but the fact that others have not reported it, and I have never seen it makes me wonder.

    The engine normally runs at about 108C and in hot weather it is not uncommon to see it climb a few degrees above that - but then the thermostate is forced open by the engine computer and the temp drops.

    When you park a hot car ten all cooling stops and residual heat in the engine will be transferred to the coolant which should then become as hot as the engine.

    The pointer of the coolant temperature gauge in the cluster is kept located in the mid-position at coolant temperatures of 75C - 113C.
    The reasoning for that is they consider that temp range to be normal operation and therefore "normal temp".

    I can see where the coolant in a a parked hot engine could easily come to 113 or higher, and if restarted in this condition then that will cause the guage to go to hot.

    As mentioned above - the puzzle is why have I never seen this even though I know I have parked a hot car and restarted it not long after.

    I think you are OK as long as it drops quickely - but to be on the safe side you should discuss with your service manager, and perhaps have error codes read.

    Cheers
    Jim Cash


  6. #6
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    Re: Coolant appears normal


    Ok, well, maybe, just maybe I might not be right :)
    I guess a student should always be respectful of his teacher, otherwise he's asking for trouble. But that was fun while it lasted! :)

    What Jim says makes lots of sense. Of course his note about us not seeing this is also important to keep in mind. One can presume the t-stat opens up quick, or is open by default, and the water pump works things through quickly. In your case, the car needs to move for it to workout??
    I doubt your t-stat is malfunctioning. I would think your problems would be more intermittent.
    Maybe itís your water pump. Maybe it takes the engine revving higher for it to work better. Maybe during traffic stops the engine block coolant doesnít have a chance to heat up to that level since itís still being moved out, albeit slowly.
    Maybe itís your mechanical fan clutch starting to fail and not gripping as well.
    Maybe your coolant is aging and just not performing as well.
    Maybe this is due to air pockets somehow; still thinking low coolant.

    It might be a good idea to flush your system and get some new stuff in there. We could box it out then about how much to overfill the tank :)
    We can also see about diagnosing some of the above components.

    Let me know. But not too early! :)
    Rajaie
    528i 5sp 06/00

  7. #7
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    Yes | No

    When my top hose blew last Thursday and I (m)

    used duct tape to get to a garage I did notice that my temp gauge was rapidly going from hot (just below the red) down to just above normal, but this was caused by the radiator cap not being tight and the water boiling (no pressure) causing air pockets (probably around the temp sensor, I believe).
    Can you turn you temp control up to 90įC with the fan on high and see if you have plenty of HOT air coming out?
    When I initially bled my system after the new hose was in place, I had heat, but it wasn't real hot so I knew that I still had air trapped in the heater core. After a while I got most of it out and the heat was very hot. Then after 200+ miles I got the low coolant alarm. Funny thing though is that the temp gauge always stayed in the correct position. Guess I was just low on coolant and didn't have enough air in system to warrant any problems.
    You could be right about it being an electrical problem. I don't know what the temp sensor resistance should be for hot and cold.

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