Lower radiator hose leak

[perttu]

Recently, as part of full cooling system overhaul, I obviously replaced all cooling hoses.

Everything else is working just fine now, but there is a small, although noticeable coolant leak, right where the lower hose connects to the radiator.

Even though the hose is definitely fully pushed into the radiator nipple (with a reassuring locking 'click'), the connection seems a bit loose. Some very small movement can be seen at the joint where hose connects to the nipple when moved by hand. Is it supposed to be this way or should the connection be super tight with absolutely no play at all?

The spare hose is from Gates, maybe there's something wrong with it. Both the radiator-side connection nipple and the hose look externally just fine. I'm wondering should I try to seal the connection somehow or buy a new OEM hose just to be sure.

 

[smorris_12]

I wonder if you've dislodged the o-ring. I always find those connectors an absolute pain to get on well, even will lubed. IME, after market stuff always seems tighter rather than looser. But the o-ring does the actual sealing rather than the plastics.

 

[perttu]

The first thing I also suspected was the hose o-ring. However, I already took the hose off once to check and the o-ring seems ok. I didn't double check the radiator however, the only part that wasn't changed in the overhaul. Getting the old (original) hose off the radiator was a huge pain and I really had to wrestle it and use a lot of force and then some. I guess it's theoretically possible that the radiator nipple took a hit, but I suspect it. Btw, is the hose's o-ring the only sealing ring in this hose-radiator connection? I'm thinking maybe I've missed something there, what I'm currently seeing is the one sole o-ring.

 

[smorris_12]

Yes, just a single o-ring. Can you identify exactly where the water's coming from? It's unusual for the bottom radiator boss to break up as it runs cooler than the upper.

 

[perttu]

I can't tell the exact spot where it leaks, but I got under the car when it was running and watched the coolant drops form and eventually fall to the ground under the connection, so the leak is definitely there. Also, other parts of the engine and cooling system look dry, so I don't think the leak originates from somewhere else.

Well, today there was a -39% day at Autodoc, so I bought a new hose and a radiator . Might as well finish the cooling system job once and for all (hopefully), even though I originally thought to do the radiator some other time

 

[patriot66]

Hi Perttu. Presuming you have an M54 engine then I suspect your leak may be coming from the small o-ring on the temperature sensor. This is a common fail and can be tricky to see. The leak runs down the hose and can be misleading as to where the source is. Take a look at this thread from February
https://z4-forum.com/forum/viewtopic.php?t=140069

 

[perttu]

Thanks for help both smorris_12 and patriot66! I replaced the temperature sensor a while back, but then again, I guess it’s no guarantee the new one does not leak for some reason. I will still double check the whole cooling system chain for leaks.

 

[patriot66]

 

[perttu]

Just to close on this, I replaced the lower hose and the radiator this week. No more leaks. Upon close inspection, the previous, almost new, hose was just fine including the o-ring, so I guess it will forever remain a mystery why it leaked. Next up, hard

 

[smorris_12]

Problem fixed. Cost will soon be forgotten!