M54 Coolant Pipe Will Not Seal!

[Andy Woods]

Hello All,

First I want to thank everybody who contributes to this forum. I am relatively new here and purchased a 2001 Z3 2.5 a few months ago. Thanks to all of the previous input that I searched through I successfully removed my intake manifold in an effort to replace the two coolant pipes underneath. I have now replaced the entire cooling system, including the two hard pipes under the manifold, but have run into a problem.

Also due to somebody's input here I decided to do a pressure test to the coolant system with a Motive Brake Bleeder and the correct fitting for the expansion tank bleeder screw. As I was pumping air into the system I thought I could hear air coming back out. It was hard to tell if it was leaking or the noise was just air running through the pipes. I was pretty sure it was leaking, and I was pretty sure it was one of the hard coolant pipes under the intake manifold. Thankfully I have not installed the intake manifold yet! Since I couldn't really tell where the air leak was I put distilled water into the expansion tank as if filling the system and sure enough, the water started leaking out of the uppermost hard coolant pipe that comes out of the side of the engine.

I figured I probably messed up the o-rings so I pulled the pipe off but the o-rings looked to be intact. My original installation included some coolant for a lubricant and the pipe seemed to go into the opening OK. So, since everything looked good I put the pipe back in and conducted the testing again but again it will not seal to the block. Same leak with air and/or water. I took the pipe back off and compared it to the old pipe and they are both identical. I even measured the inside diameter and outside diameter of both pipes including the o-rings and everything is identical. The old pipe was very difficult to remove and I broke the mounting tab in doing so, though the pipe was still intact, so I re-installed the old pipe and got the same result. Both pipes leak air or water, whichever test I choose to use. I examined the port in the block and it looks good, I don't see any cracks or chipping around the edges and it's clean. It seems like the port is too big or the pipe/o-rings are too small.

Any suggestions? What am I missing?

Thanks for you help,

Andy

[Wrench Turner]

Hm. I did this on my m54b25 in my e46 this past summer and everything sealed up perfectly fine. When I removed mine, it practically disintegrated, half of the pipe remaining lodged into the port on the engine. I had to pick it out slowly and then needed to sand the port itself to remove everything. Old pipes has just over 200k miles on them though...

Everything you are saying seems to be spot on in terms of installation. Did you use OEM parts for this? Were the O-rings supple and not hard? Are absolutely positive the pipe is fully seated? They take a bit of effort to seat fully. Is there any corrosion present on the upper port into the engine (mine has stupid amounts of corrosion I had to take care of)? Some people have reported using RTV sealer on these pipes but that really shouldn't be necessary.

[s8ilver]

Oh, that was fun job. NOT!

I concur with sanding the inlets. I had a lot of old gunk on mine and used a piece of Scotch Brite to get the bigger bits off (used a tiny angled exacto to pull as much of the looses pieces out as possible). Then I followed up with some fine grit sandpaper before I reseated the new pipes. The only thing I can think of if your pipes are seated properly and the gunk is all gone is that there is some pitting beyond what the o-rings will seal. Perhaps get an inspection mirror down there and look at every surface you can. I know the area is a pain to work in.

I might have been the one that suggested the Motive bleeder as that's how I tested mine. However, I ran the pressure test BEFORE I pulled the old pipes off and the system held pressure somehow. I was convinced my leak only occured when the motor was up to temp. But of course, without a manifold and all the hoses disconnected, I wasn't about to start the motor to find out. I found evidence of coolant trails near the pipe ends, so was certain I found my mysterious leak. After replacement, she hasn't leaked since.

My post from a while back:
https://www.bimmerforums.com/forum/s...ur-water-pipes!

[Andy Woods]

What am I missing?

Thanks for you input, I really appreciate it. Now for the laugh! I WAS missing something. After messing with this coolant pipe for most of the day I decided to take the other coolant pipe off just in case and sure enough those o-rings were messed up! It was very difficult to tell where the leak was actually coming from between those two pipes. I inspected the port and found hard rubber from the previous o-rings so got that out with a dremel tool and a soft brush. I put new o-rings on that pipe and installed, and put two old o-rings on the upper pipe and installed, and ran the air test again and voila! No leaks this time. So now I will obtain new o-rings for the upper pipe and replace those old o-rings before I proceed.

Thanks again for your help. I hope you didn't rack the brain too much!

Andy