Hi guys,

I bought and fitted a new thermo etc yesterday, all went well, refitted all the new parts - thermo and o-ring, bolted all back and topped it up. I then started it and I lost a whole load of coolant. After inspection it escapes from between the thermo housing and the block/thermo.

All the parts are genuine VAG. It was tightened enough and from what I gather the o-ring was in the correct position.

I really don’t know what it could be.

The o-ring looks the same as the old one but I’m thinking they may have given the wrong one?

Any suggestions would be a great help.

The o-ring might have slipped out of its seat when you were tightening up the bolts, and it's pinched between the housing and the block, causing a gap.

Or the bolts haven't pulled up fully because the housing is misaligned.

Your best bet will be to whip it off, inspect it all, and re-install. I'm sure it'll become obvious then.

It could certainly be the wrong O-ring.

I had mine done before Xmas by a local VW specialist, using genuine parts I picked up from the local dealers. When I went back to pick up the car the mechanic told me that the supplied O-ring turned out to be slightly too large, but the old one was still servicable so they re-used it.

Possibly a VAG QA problem, or maybe just a mistake by the dealers parts dept.

I had it on and off loads yesterday. It is definitely aligned in the block. When I took it off it was still there. It seems to fit the diameter, I was thinking it might not be thick enough. The housing is tight to the block -it wont go any tighter, just doesn't seem to grip on the o-ring.

I still have the old o-ring but don't want to use it. I'm going to ring the dealer on Mon.

I need it done by Mon too because I have booked it in for the clutch/flywheel for Tue. :wonder:

I'm going to have another go at it tomorrow. I was thinking of buying a cheap QH thermo from halfords and using the seal in that. They have paper seal things that sit between the housing and block in too. Might help...

I've had another look this morning and think I may have found the culprit. The o-ring appears to be the same diameter and thickness as the old one.

I think it could be one of two things, or both:

The thermostat housing seems to be warn slightly - where the o-ring makes contact.

Also the block looks as if its started to erode!

I'm of to Halfrauds to get some gasket seal and go for a more "permanent" solution.

It took me ages to do my Mk1. Dont do what I did and over tighten the bolts. I stripped one and had to tap another thread. Best to take the hose off the cover, put the O ring on the cover first using a sealer, make sure its central. Thermostat in the block then using sealer fit cover with O ring attached. Use plain water to make sure it dont leak, when ok drain some and top up with anti freeze.

Yea thats basically what I done - put gasket seal on the housing, placed the o-ring, a bit of seal on the outer part of the ring and fitted. I ran it for 20 minutes and it didn't leak

from those pics it looks like the old o ring is still sat in place.... please tell me its not?!

forgive me if i am wrong..... but i have highlighted in red where it looks like the old o ring still sits. if this is the case then that needs to be removed straight away and replaced with your new o ring. having 2 o rings fitted is probably whats causing the loss of coolant and the bend/warping of the thermo plastic housing as you tighten it up

Edited 21 February, 201115 yr by vrs200bhp

forgive me if i am wrong..... but i have highlighted in red where it looks like the old o ring still sits. if this is the case then that needs to be removed straight away and replaced with your new o ring. having 2 o rings fitted is probably whats causing the loss of coolant and the bend/warping of the thermo plastic housing as you tighten it up

LOL that was the new o-ring. Its still there - surrounded by a layer of gasket seal so its going nowhere fast

Eh..should the o ring not be in the groove on the cover/housing???

Edited 21 February, 201115 yr by kenny rsell

Yes, it should sit on the face against the plastic housing!

LOL that was the new o-ring. Its still there - surrounded by a layer of gasket seal so its going nowhere fast

the old "o" ring you mean? im confused. :'( the new o ring is clearly in shot the red arrow points to something behind the new o ring, is that not the old one?

Eh..should the o ring not be in the groove on the cover/housing???

Yes, it should sit on the face against the plastic housing!

It was placed on the housing when I initially fitted it on Friday, this was taken on Sunday, when I had removed the housing and the o-ring was sat there as it is in the pic. It was re-placed on the housing with gasket seal which seemed to solve it.

the old "o" ring you mean? im confused. :'( the new o ring is clearly in shot the red arrow points to something behind the new o ring, is that not the old one?

There is only one o-ring in there. The old one was "chucked" on Friday. I think its the reflection of the thermostat on the o-ring?

Edited 21 February, 201115 yr by JohnRS

There is only one o-ring in there. The old one was "chucked" on Friday. I think its the reflection of the thermostat on the o-ring?

ok mate just checking