Thermostat housing leak?

[breeze]

I’ve replaced my pickup, resealed the sump and replaced my oil filter housing (oil leak; I decided to do the whole housing rather than risk it being warped). All good.

However, when refilling with coolant, I noticed a leak around the alternator. If topped up to the max level, the car will loose a bit of coolant until it drops down to min, and then stop dripping.

Any ideas? It isn’t that easy to see the source of the leak. I am wondering whether the pattern of coolant loss could provide a clue. At the moment, I think a cracked thermostat housing is most likely. I suspect linked to tugging the coolant lines trying to get to the bolts on the oil cooler.

Not looking forward to stripping everything down again! 

[LC5F]

It could be anywhere fella - assuming you are running coolant - best bet is to let it dry off and it will leave a milky residue showing where its coming from.

[breeze]

Returning after 24 hours, almost all the coolant had leaked out. Keeping the expansion cap on is probably slowed it before.

Having removed the alternator for better visibility I can see the thermostat housing is cracked on the join for the radiator (I think that is what it is) elbow. It did have a minor leak, I suspect my work over the last couple of days finished it off. New housing required.

Not the most pleasurable job, but it looks to be more straightforward than the oil filter housing (which was painful).

[breeze]

Odd experience. I replaced the thermostat housing with a genuine VW part, torqued to factory specs (15nm) and even tested with a pressure tester before buttoning up.

Car was fine for around 150 miles. I took it for a drive today and got a warning light for low coolant. Looked underneath and it was dripping.

I stripped it all down and found that the housing bolts were loose. Odd, because I definitely went to factory spec and did do a pressure test. With the pressure tester at the same pressure it was leaking.

I am thinking that the bolts somehow have backed out. I re-torqued to 17nm and put back together. So far looks OK.

I’m wondering whether the bolts have been over torqued in the past and that has affected the threads. Kicking myself for not using a thread lock but hoping 17nm is enough.

Thoughts?

I can’t recall whether the factory bolts had any thread lock, but nobody online replaces them.

[RBS]

The “big” thermostat housing to the block is 9NM!
I’ll try to get you a pic with all the torque specs for the thermostats and important change all the rubber O rings!

[RBS]

Oops!!! Sorry you were right!!! It’s 15NM!!!

[RBS]

[breeze]

Thanks for sharing and yes, 15nm! 

That image has got me thinking... I can see that the water pump is very close to the area of the thermostat. It hadn't quite occurred to me that the leak that I am seeing might not be the thermostat housing. Is there an easy way to see if the leak is from the water pump? That would be funny...!

It doesn't quite fit the story, but I think it would be good to double check.

[RBS]

The easiest/best way is to get the upper timingcover off.
Then with a light or camera you could see it... but my guess is the thermostat housing.
If the waterpump should be leaking then the leaking should go down not arround...

[breeze]

The easiest/best way is to get the upper timingcover off.
Then with a light or camera you could see it... but my guess is the thermostat housing.
If the waterpump should be leaking then the leaking should go down not arround...

The coolant appears to drip from the centre front of the oil pan.

There is liquid behind the AC compressor, on the little ledge on the block and that area is between the thermostat housing and water pump (albeit the pump is around the corner if that makes sense).

Yesterday I took the upper timing cover off but couldn’t really get much of a view of the pump. I did have a look with a light, will try again.

I must say I have done so much work on this car recently that I will probably give this one to a mechanic. That includes all engine mounts and cleaning behind wheel arch liners, would have been the perfect time to do the belt and pump.

To those of you that have had a water pump leak… where does the leak show up? Knowing that would help.

[OllieVRS]

My leak was the small seal on the thermostat labeled number 5, rightmost next to number 20 on the diagram posted earlier. I found this out by digging around with my cheap endoscope and finding coolant around where that metal coolant pipe met the thermostat (but no coolant higher than that connection).

I replaced the whole thermostat and that seal just in case the seal wasn't the leak and that fixed it.

[breeze]

My leak was the small seal on the thermostat labeled number 5, rightmost next to number 20 on the diagram posted earlier. I found this out by digging around with my cheap endoscope and finding coolant around where that metal coolant pipe met the thermostat (but no coolant higher than that connection).

I replaced the whole thermostat and that seal just in case the seal wasn't the leak and that fixed it.

Already replaced all of the above! Parts from the main dealer.

[breeze]

If anybody is curious… I ended up taking it to a specialist.

They found two leaks; one at the thermostat housing for a pinched o-ring (I think the one to the block - so an installation error on my part) and one at the water pump.

Slightly kicking myself because I am normally meticulous, but I guess these things happen. At least it is nice knowing that the cambelt and water pump are done - they weren’t far off being due.

[RBS]

@ breeze: I’m glad it’s sorted out for you It’s not easy sometimes to troubleshoot…

[pudding]

Oh well, glad it's sorted. To avoid O ring misalignment, I usually set it in place with silicon grease, or a very thin smear of silicon sealant.  It stops the O ring popping off when you're wriggling the housing into place.