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Thread: e38 750il Slow Coolant leak

  1. #1
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    e38 750il Slow Coolant leak

    Hello,

    I had my water pump and thermostat replaced about a month ago. Last week when checking coolant level It went down to the point where I had to refill.
    Now its going down below normal level after 4 days of driving, and sometimes I can see coolant on the floor when parked for a while.

    Not positive but When looking at the front of the engine it looks like its coming from the water pump area. I can see drive coolant.

    Any idea where it maybe leaking from? I hope its not from the water pump as am not ready to remove it again.

    Please healp

  2. #2
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    If yours is facelift look at the small vent hose that T off on top coming out right next to oil-filler cap. It could be leaking from that hose, and sipping coolant from there.

    Second place to look at is the mid size hose coming front the bottom of the water pump into the expansion tank, its very hard to see but the belt could touch it and cut into the hose causing a sipping leak.

  3. #3
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    Quote Originally Posted by asianvenom View Post
    If yours is facelift look at the small vent hose that T off on top coming out right next to oil-filler cap. It could be leaking from that hose, and sipping coolant from there.

    Second place to look at is the mid size hose coming front the bottom of the water pump into the expansion tank, its very hard to see but the belt could touch it and cut into the hose causing a sipping leak.
    yes it is a facelift. the vent hose cracked one day and was replaced when new water pump and thermostat were replaced.
    Am going to take a look at the hose from extension tank to water pump. Will try to take pics

  4. #4
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    Instead of guess have the system pressure tested.
    If you're not experienced (and by your question I assume you're not) leaks may look like they start in one place but maybe somewhere originate else.

    Check engine light (CEL) means 'Cost Estimate Large'
    I've spent most of my money on this car the rest I just pissed away

  5. #5
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    Quote Originally Posted by ebida3 View Post
    Instead of guess have the system pressure tested.
    If you're not experienced (and by your question I assume you're not) leaks may look like they start in one place but maybe originate somewhere else.

    Check engine light (CEL) means 'Cost Estimate Large'


    Check engine light (CEL) means 'Cost Estimate Large'
    I've spent most of my money on this car the rest I just pissed away

  6. #6
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    Quote Originally Posted by asianvenom View Post
    If yours is facelift look at the small vent hose that T off on top coming out right next to oil-filler cap. It could be leaking from that hose, and sipping coolant from there.

    Second place to look at is the mid size hose coming front the bottom of the water pump into the expansion tank, its very hard to see but the belt could touch it and cut into the hose causing a sipping leak.
    seem like its coming from behind the water pump, can see the coolant behind the Vibration damper. I was also able to see a drip from a hard hose that does into the water pump on the driver side. you can see it on the pics below.

    IMG_1513.jpg IMG_1514.jpg IMG_1516.jpg IMG_1515.jpg IMG_1517.jpg

  7. #7
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    Quote Originally Posted by masu3701 View Post

    yes it is a facelift. the vent hose cracked one day and was replaced when new water pump and thermostat were replaced.
    Am going to take a look at the hose from extension tank to water pump. Will try to take pics
    I'm not talking about that vent hose...I'm talking about the vent hose that t off of it and goes under the intake manifold, into the valley pan. You can not replace that hose without removing the intake manifold.

  8. #8
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    Quote Originally Posted by masu3701 View Post
    seem like its coming from behind the water pump, can see the coolant behind the Vibration damper. I was also able to see a drip from a hard hose that does into the water pump on the driver side. you can see it on the pics below.

    IMG_1513.jpg IMG_1514.jpg IMG_1516.jpg IMG_1515.jpg IMG_1517.jpg
    IMG_1518.jpg IMG_1526.jpg

  9. #9
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    Quote Originally Posted by asianvenom View Post
    I'm not talking about that vent hose...I'm talking about the vent hose that t off of it and goes under the intake manifold, into the valley pan. You can not replace that hose without removing the intake manifold.
    you talking about the vent hose that goes from the front center of the top of the engine to the top of the radiator and T into the water pump?
    24568_x800.jpg ??

    If thats what you're talking about, yes it was replaced, and yes I had to remove the intakes in order to access it.

  10. #10
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    Yes...you're a good man. Other that if its behind the water pump, then its leaking from the coolant tube is a good suspect.

  11. #11
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    Quote Originally Posted by asianvenom View Post
    Second place to look at is the mid size hose coming front the bottom of the water pump into the expansion tank, its very hard to see but the belt could touch it and cut into the hose causing a sipping leak.
    +1 on checking this hose. Be aware that this hose is moulded with a flattened section from the factory in order to clear the belt, so don't be fooled into thinking its deformed.

    However, it does balloon a little over time, and as soon as this happens you see wear marks on the hose. Really, anyone doing the 750 WP should replace this as a matter of course.

    At the rear of the WP are 2 tubes. The smaller one has a black coating applied to the end, where the o ring sits and seals to the WP. Unfortunately, this flakes off in places so there is a possibility of a leak here.

  12. #12
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    Quote Originally Posted by chrisn7 View Post
    +1 on checking this hose. Be aware that this hose is moulded with a flattened section from the factory in order to clear the belt, so don't be fooled into thinking its deformed.

    However, it does balloon a little over time, and as soon as this happens you see wear marks on the hose. Really, anyone doing the 750 WP should replace this as a matter of course.

    At the rear of the WP are 2 tubes. The smaller one has a black coating applied to the end, where the o ring sits and seals to the WP. Unfortunately, this flakes off in places so there is a possibility of a leak here.
    Any picture of the that goes from extension tank to water pump? When I trace the hose from the bottom of the extnsion tank I see the other end goes into the engine I believe.

    I can see coolant from the hose on this picture but not sure were it does. I can see drips from where this hose connects to bottom of water pump on the driver side, but dont see where it ends.

    IMG_1516.jpg IMG_1526.jpg

  13. #13
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    This hose is quite short, going only between the expansion tank and the WP. Unfortunately it is not possible to see the WP end with everything assembled. Indeed there is so little clearance that there is not room for a typical worm drive hose clip. BMW used a single-use crimp type clip to overcome this problem.

    In your image, as best as I can judge, there are a couple of hoses on that side connected to the oil cooler. Look at Realoem / Engine / Cooling system water hoses - to see where they attach.

  14. #14
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    I believe the coolant is leaking from the back of the water pump between the water pump and the block. Once pressure builds up I can see coolant coming slowly at the top of the water pump where it seats against the block.

    in this picture, the coolant is leaking around the edges where i marked in read. I can definitly see it coming out from the top, not sure about the bottom but can see its wet. SO cant confirm that the bottom side is leaking.

    Screen Shot 2017-06-18 at 8.06.25 AM copy.png


    Now do i need to remove the water pump in order to fix the leak? Trying to avoid remind it as much as I can.
    Hope I can just seal it somehow while mounted on the block without removing it.

    What do you guys think?

  15. #15
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    Quote Originally Posted by masu3701 View Post
    I believe the coolant is leaking from the back of the water pump between the water pump and the block. Once pressure builds up I can see coolant coming slowly at the top of the water pump where it seats against the block.

    in this picture, the coolant is leaking around the edges where i marked in read. I can definitly see it coming out from the top, not sure about the bottom but can see its wet. SO cant confirm that the bottom side is leaking.

    Screen Shot 2017-06-18 at 8.06.25 AM copy.png


    Now do i need to remove the water pump in order to fix the leak? Trying to avoid remind it as much as I can.
    Hope I can just seal it somehow while mounted on the block without removing it.

    What do you guys think?

    SO I took off the fan and the upper radiator hose so that I can get a good view of the leak. I found that the upper water pump bolt was very loose and that was the same area I was seeing coolant coming out under pressure. So I put some gasket maker sealant around the upper part of the water where it goes against the block ( as shown in red on the picture above) and tightened the loose bolt. That bolt is where I put the red arrow on the picture. I couldnt reach the bottom part of the water pump, so left that part alone.

    Put everything back together and reused the same coolant I have drained. Took it on test drive. I dont see the leak but am getting low coolant level

    Will let it coolant down and check level tomorrow.

    Hopefully that fixed the issue.

  16. #16
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    The sealant won't really do anything, its the O ring that does the sealing - and you did replace it didn't you? In view of the effort involved in this job I replaced every single seal = no leaks

  17. #17
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    Quote Originally Posted by chrisn7 View Post
    The sealant won't really do anything, its the O ring that does the sealing - and you did replace it didn't you? In view of the effort involved in this job I replaced every single seal = no leaks
    Well the water pump is fairly new with new O rings and everything. Maybe that loose bolt was letting coolant out.
    Will see what happen.

  18. #18
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    I found the second source on my coolant leak which is at the small water pipe that goes into the right side ( driver side) of the water pump.
    On the picture below, It is leaking from #7 where I have the red arrow.

    Screen Shot 2017-06-23 at 10.11.04 PM copy.png IMG_1559.jpg IMG_1561.jpg


    Has anyone had to deal with this pipe before? How do you secure it in to prevent leaks? I couldnt find a part number for the O ring what goes into the small hole on the water. Real realOEM does show that hole on the picture or an O ring for it.

    Please advise on how to seal it properly to prevent leaks.

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