550i coolant leak detected, your expert advise?
#1
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My Ride: E60 550i
Model Year: 08
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Had hard time finding out where is coolant leaking from, every 3-4 months have to add about 1-2 quarts of coolant.
Finally located, with engine hot removed the expansion tank mounts and noticing under the tank dripping coolant from the bottom hole.
Last year I replaced the expansion tank cap just as preventive measure (so cap is fairly new) but it does not appear to be normal having this much coolant loss that happens at engine normal operating temps.
Would it be safe to conclude the tank needs replacement?
img host
![](https://i.postimg.cc/RVTXQGJ2/cl2.png)
![](https://i.postimg.cc/pTYFbcvH/cl3.png)
Finally located, with engine hot removed the expansion tank mounts and noticing under the tank dripping coolant from the bottom hole.
Last year I replaced the expansion tank cap just as preventive measure (so cap is fairly new) but it does not appear to be normal having this much coolant loss that happens at engine normal operating temps.
Would it be safe to conclude the tank needs replacement?
![](https://i.postimg.cc/BvZWBXvB/cl1.png)
![](https://i.postimg.cc/RVTXQGJ2/cl2.png)
![](https://i.postimg.cc/pTYFbcvH/cl3.png)
#3
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My Ride: E60 550i
Model Year: 08
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Still not clear how does this process work in terms of releasing coolant at high pressure levels, between the cap and the tank?
Is it possible that even the cap is good the tank can be defective causing coolant loss via that hole?
I can say this was kind of pain to detect as it leaked under the tank (not visible) and every time coolant would dry very quick from heat.
#4
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My Ride: 2008 550i
Model Year: 2008
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If your tank was original from new, it was due for a replacement. The cooling system is pressurized while the engine is running, and when the tank is nearing the end of its life, around 10 years, the plastic cannot withstand the high pressure anymore, and will develop cracks. Most of the time, they are on the side and is visible with dried blue coolant stains. Yours happened to crack on the bottom.
Ideally, this part should have been made out of metal, but beans have to be counted.
Ideally, this part should have been made out of metal, but beans have to be counted.
#5
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If your tank was original from new, it was due for a replacement. The cooling system is pressurized while the engine is running, and when the tank is nearing the end of its life, around 10 years, the plastic cannot withstand the high pressure anymore, and will develop cracks. Most of the time, they are on the side and is visible with dried blue coolant stains. Yours happened to crack on the bottom.
Ideally, this part should have been made out of metal, but beans have to be counted.
Ideally, this part should have been made out of metal, but beans have to be counted.
#6
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My Ride: 2008 550i
Model Year: 2008
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Mine lasted 10 years, but others might have shorter lifespans, depending on how much mileage they drive. And believe it or not, but all of my rubber cooling hoses are still in good condition. When I replaced my second water pump six months ago, I checked all the main radiator hoses. The only hoses I replaced so far are both tank return vent lines, which only failed from the plastic tube connectors on them disintegrating, the rubber tube portions were still useable.
#7
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Mine lasted 10 years, but others might have shorter lifespans, depending on how much mileage they drive. And believe it or not, but all of my rubber cooling hoses are still in good condition. When I replaced my second water pump six months ago, I checked all the main radiator hoses. The only hoses I replaced so far are both tank return vent lines, which only failed from the plastic tube connectors on them disintegrating, the rubber tube portions were still useable.
![Wink](https://5series.net/forums/images/smilies/imported/wink.gif)
#8
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My Ride: E60 550i
Model Year: 08
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Just to clarify, there is no crack at the bottom, coolant is dripping from very top point through that bottom hole. When checking with light it appears there is a small hole at the top, maybe that is the same valve hole that releases coolant at very high pressure levels in case of overflowing the tank.
Currently have 130K and this is original expansion tank, 2008 550i model.
Currently have 130K and this is original expansion tank, 2008 550i model.
#9
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Just to clarify, there is no crack at the bottom, coolant is dripping from very top point through that bottom hole. When checking with light it appears there is a small hole at the top, maybe that is the same valve hole that releases coolant at very high pressure levels in case of overflowing the tank.
Currently have 130K and this is original expansion tank, 2008 550i model.
Currently have 130K and this is original expansion tank, 2008 550i model.
#10
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My Ride: E60 550i
Model Year: 08
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The cap relieves the pressure but is that extra coolant also dripping via same hole as shown in my pictures?