Coolant leak near plastic pipe troubleshooting - thoughts?

[troman]

Hi everyone. I'm hoping someone might give me some insight on this problem I'm having:

I seem to have a coolant leak where the plastic return pipe comes out of the block. Coolant pools in the small concave area right under the pipe. I have replaced the O ring, but the pipe seems to be separating from the block and weeping coolant, as if there is a lot of pressure pushing it out.

Coolant temp never gets to the exact middle of the gauge; it always sits one click below, or just a bit above that. I'm running 50-50 mix of dealer blue coolant.

I noticed yesterday, after running errands, that the coolant hose going into the radiator was hot (normal), but that the throttle body heater plates (vertical and horizontal) were cool, and the metal "u-turn" connector that connects the two combo coolant/pcv (?) hoses under the intake was also cool.

It seems to me that the throttle plates and the "mess under the intake" metal pipes should be full of hot coolant, right?

Since they are cool, and the radiator hose is its normal hot temperature might there be a blockage? Could this cause pressure to build up in the plastic pipe, making it separate from the block (we're only talking one millimeter, but noticeable that it isn't perfectly flush), and therefore leak?

It'll drop about three inches in the coolant overflow tank about every two weeks, and there is always coolant pooled in the area under the pipe.

Best regards,

Tim

[romkasponka]

On the plastic pipe in the block there is O-ring. I have seen few time this pipe cracked near the O-ring. Could be leak source because there is not enough pressure on O-ring to seal pipe.

[DesktopDave]

+1 - that o-ring tends to fail and high-pressure coolant weeps out. I wouldn't think there was any blockage, even though the pipes are cool. They don't tend to flow very much coolant. Be sure the car is bled correctly - they do tend to get vapor lock in that case.

Don't consider replacing the o-ring alone. Every time I've taken one of these plastic coolant pieces out, it's cracked in my hands. Be sure you get the stock BMW OEM piece too, the aftermarket URO one doesn't fit correctly. I'd also strongly recommend a pressure test of the entire system after you've replaced the coolant piece.

[troman]

Thank you for the feedback.

The plastic pipe is new in the last two years, and the o-ring is brand new...yet that seems to be the point of failure, in that the pipe seems to be separating from the block by about a millimeter.

I do have an extra radiator cap - I think I need to make a pressure tester, like you're suggesting. See if if holds pressure, and maybe spray some soapy water around the connections.

Thanks!

[DesktopDave]

Are you sure the pipe is OEM? Was it installed by a dealer? I've seen a few (non-BMW) dealers use generic parts instead of OEM. Many indies will use them too.

The Uro part is cast with a very slight angle - so the flange won't sit tightly against the block. That's the problem with them. Some will work temporarily, but the OEM part is the permanent solution.

[troman]

Conveniently, you can look up past orders on Pelican Parts....the pipe is the OEM version.

This piece of junk, though (11-15-1-739-266-M253 combo breather hose), was APA brand, and it broke apart after a month, and had to be replaced with OEM.