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Thread: 740 overheating, help!

  1. #1
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    740 overheating, help!

    I recently changed the coolant tank as there was a water leak. Now after the car being on for around 45mins-1 hour the temperature starts rising.

    Any ideas?
    BMW 840, INDIVIDUAL DAYTONA PURPLE , 20 INCH ALLOYS, MAGNAFLOW QUAD EXHAUST SYSTEM , CSI BODYKIT, CARBON FIBRE BADGES, BILSTEIN SHOCKS, ELBACH LOWERING SPRINGS, ALPINE HEADUNIT WITH 12 INCH SUBS.

  2. #2
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    Quote Originally Posted by Naz840 View Post
    I recently changed the coolant tank as there was a water leak. Now after the car being on for around 45mins-1 hour the temperature starts rising.

    Any ideas?
    Did you bleed the cooling system properly?

  3. #3
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    Quote Originally Posted by purplecty View Post
    Did you bleed the cooling system properly?
    Yes, the system was bled properly.
    BMW 840, INDIVIDUAL DAYTONA PURPLE , 20 INCH ALLOYS, MAGNAFLOW QUAD EXHAUST SYSTEM , CSI BODYKIT, CARBON FIBRE BADGES, BILSTEIN SHOCKS, ELBACH LOWERING SPRINGS, ALPINE HEADUNIT WITH 12 INCH SUBS.

  4. #4
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    Bleed it again. Nothing else changed, except you opened the system introducing air. More than likely that is the problem.
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  5. #5
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    .....and:



    Last edited by Timm; 10-16-2020 at 03:38 PM.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  6. #6
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    Quote Originally Posted by Timm View Post


    .....and:



    I’ve noticed that when the car is at full temperature the fan is only going around at the same speed even when you increase the revs.

    I think the fan might need changing? Doesn’t feel as strong as my fan on my 840.
    BMW 840, INDIVIDUAL DAYTONA PURPLE , 20 INCH ALLOYS, MAGNAFLOW QUAD EXHAUST SYSTEM , CSI BODYKIT, CARBON FIBRE BADGES, BILSTEIN SHOCKS, ELBACH LOWERING SPRINGS, ALPINE HEADUNIT WITH 12 INCH SUBS.

  7. #7
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    Quote Originally Posted by Naz840 View Post
    I’ve noticed that when the car is at full temperature the fan is only going around at the same speed even when you increase the revs.

    I think the fan might need changing? Doesn’t feel as strong as my fan on my 840.
    Fan as in fan clutch? If so time to replace it...

    https://www.fcpeuro.com/products/bmw...m-11527502804b

  8. #8
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    If the temp is going up when moving, then it is likely not the mechanical fan or fan clutch. Are you in the UK? If so, the ambient temp is low enough to not be a factor. If it creeps up in traffic, stop lights, then look at it. Also, if this is new behavior since you swapped the overflow tank, then it’s a bleeding issue. I know, you don’t want to hear that. Did you put the heat on full hot, and the fan on high?

  9. #9
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    I'm with CPHES! There is probably still air bubbles trapped in the system somewhere that need to be bled out. Raising the front end up helps as well. These can sometimes be tricky to bleed properly...

  10. #10
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    My e38 was the most difficult BMW I've had to bleed to date. Took multiple times, even using Tim's method.

  11. #11
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    Quote Originally Posted by Naz840 View Post
    I recently changed the coolant tank as there was a water leak. Now after the car being on for around 45mins-1 hour the temperature starts rising.

    Any ideas?
    What else did you change besides the coolant tank? If nothing else, I know it is hard to believe but you have a pocket of air in the system. The only other item that would cause this is blockage of some type and we know that is not the problem. When there is air in the system, some of the radiator fluid is no longer moving through your system. Put your car on an incline and follow exactly the video above.

  12. #12
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    Also, how much coolant came out when you changed it, and what bleeding procedure did you use the first time? Are you watching the temp gauge, or are you watching the temp from the secret menu on the cluster?

  13. #13
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    **Update** replaced the viscous fan and it has solved the overheating issue!

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