New Upper Radiator Hose Leaking Coolant

[bimmer48i]

Hello all,

I recently decided to completely overhaul the cooling system in my 2009 E70 4.8i xDrive (N62B48). This included,

1. Expansion Tank and cap (1.4 Bar)
2. New cooling system hoses including Y hose under throttle body
3. Geniune BMW Water pump
4. Mahle Thermostat (90c from ebay)
5. Bimmerfix Stent

I installed everything, connected all the hoses properly until I heard the click sound. Filled it with BMW Blue Coolant mixed with distilled water.

Initiated the self-bleeding process, and filled her up. Drove for 10 minutes around the neighborhood, came back and parked the X5.

After it cooled down, I checked the coolant level in the Expansion tank and it was low. It wasn't low enough to throw the 'Low Coolant" warning but low. I added the coolant again, drove for 10 minutes and same thing happened again.

Performed a pressure test and turned out the coolant is leaking from upper radiator hose where it connects to water pump. I removed the hose, inspected inside and there was no debris or anything. The water pump surface is clean too, since they both are new and Genuine BMW parts.

I connected the hose until I heard the click sound again and filled the coolant. I even double checked that the hose was connected properly into the tiny slot it has. Unfortunately it still leaks in that place.

I've exhausted all my options that I knew of. Any help or pointers would help.


Sorry about the long post; it's my first post.

[Black-Forest]

Check the O-ring in the hose for any missing chunks. Potentially it may have been damaged when installing. I usually smear a bit of silicon grease on them to prevent damage.

[Cyrix2k]

I agree with Black-Forest, although I usually just wet the o-ring with coolant. If the o-ring is damaged, you can pop it out and may be able to find a replacement locally.

[ard]

I spit on it.

[bimmer48i]

Thank you all. I did use the coolant to lubricate the O rings but I'll inspect O ring again and lubricate once more. Hopefully that will fix it.

I bought the parts from FCPEuro so my last resort is to get replacement part under lifetime warranty (although I really don't want to do this ).

[twarr1]

The o rings are an oddball metric size. Almost impossible to find.
Make sure the plastic spacer didn’t fall out at some point.

[LightlyToasted]

Originally Posted by twarr1

The o rings are an oddball metric size. Almost impossible to find.
Make sure the plastic spacer didn’t fall out at some point.

Plastic spacer is critical. When I replaced my upper hose I forgot it or misplaced it and it leaked all over the place. Luckily the old hose with spacer was still in the garbage.

[bimmer48i]

So I replaced my new hose with newer one (Thanks to FCPEuro’s Lifetime Warranty). Filled her up with BMW blue, pressure tested, and no leaks!! Was really excited, test drove and what do you know, the coolant level had gone down.

Although I had self-bled the system, I gave her the benefit of the doubt that there was some air in the system. So added the coolant, test drove again but coolant went down again.

I don’t see any leaks dripping out.

I’m totally lost here and honestly I’m tired. I literally overhauled the entire cooling system and still it’s losing coolant.

Any ideas where is it going? What can I check next?