Wanted - Thermostat gasket/seal

[Wooscary]

Hello

Mine is leaking and hard to figure out, are these a rubber seal or is it made up of a liquid sealant?

Can I just walk in to a car parts place and ask for one, or is it a special thing?

Also, I suppose while I'm at it, might as well change the thermostat, there are various sizes right? Again, available from the usual Euro Car Parts type place?

Cheers.

[mat_fenwick]

It's a rubber seal which should come with a new thermostat. I'd be slightly concerned why it's suddenly started to leak though - do the hoses feel very hard when the engine is warm?

There are two sizes of thermostat I know of, early larger one held in with a circlip but I'm pretty sure from seeing photos of your engine yours is the later one which is easier to change. A photo would confirm though. Should be available from any motor factors still.

[Dollywobbler]

Actually, I could do with a thermostat gasket for my Mk2. (larger in-housing type). I mauled it a bit when I fitted the new 'stat about 30,000 miles ago and it is losing coolant. I'd like to get that sorted before the winter. Can you get gaskets separately?

[mat_fenwick]

Not sure TBH, but if you can measure up what size it is I'll have a look what I have here. I've got the remains of two head gasket sets which seemingly came with gaskets for every variant of the XUD, and I wouldn't have used the larger 'stat seal. I can pop it in with your gearknob which I've just sealed up...

[Wooscary]

The hoses don't feel hard. The radiator feels very hot everywhere but a small patch in the middle at the bottom (does this reveal anything?).

It looks like the seal has just gone very crusty, bits of it are falling off on the outside all over the place.

When I squeeze the hose which goes in to the front of the 'stat housing, there is a bit of a whoosh like air is being pushed through something. So maybe air is getting in where the seal is bad? Very hard to tell at exactly which point the water is escaping as it dries up/evaporates so quickly, but it does seem to be pooling on the front of the housing where the top bolt is.

Some pictures.




Possibly more worrying is spotting some tiny bubbles in the header tank. Ummm!

Cheers.

[Wooscary]

Well I've ordered a new thermostat with gasket, will try fitting that tomorrow and see what it looks like.

Anything I should be aware of with fitting one?

Cheers.

[mat_fenwick]

The cold spot on the radiator is likely a partial blockage - I would be inclined to flush the system with a hosepipe once the thermostat is out. Just push the nozzle into the housing on the engine where the thermostat was and give it a blast until clear water appears from the radiator top hose. Repeat with heater on and off to also flush the matrix to some extent.

Is there any hiss when you remove the expansion bottle cap say a minute after a cold start? Bubbles when running would concern me.

[citronut]

Anything I should be aware of with fitting one? Cheers.

clean all the mating surface's then dont over toghten the cover on re/fitting, as the crack

regards malcolm

[Wooscary]

The cold spot on the radiator is likely a partial blockage - I would be inclined to flush the system with a hosepipe once the thermostat is out. Just push the nozzle into the housing on the engine where the thermostat was and give it a blast until clear water appears from the radiator top hose. Repeat with heater on and off to also flush the matrix to some extent.

Is there any hiss when you remove the expansion bottle cap say a minute after a cold start? Bubbles when running would concern me.

Mat, thanks for the thoughts.

I was thinking I'd definitely flush it at the same time as I've been topping up with tap water.

A little bit of a hiss, I'll test more carefully. Would that suggest pressure in the system? Should it be under pressure? Bubbles worry me too, I could only spy them after turning the engine off however. Could they be appearing due to air getting in at the perished gasket? Suppose I better start checking for other symptoms? Water in oil?

There doesn't appear to be any difference in performance, and any water loss seems accounted at the 'stat.

Malcolm, thanks for the tip!

Cheers. This should probably have been in Technical. Oh well!

[mat_fenwick]

A hiss before any temperature build up suggests combustion gases are leaking into the coolant, as without heat there should be no pressure. I can't see how air could be drawn in through a damaged seal, as the pressure in the cooling system will never be lower than atmospheric.

Seen a few XUD failures (including mine!) where there is no detectable loss in performance, and the only outward clue was weeping at hose junctions etc. A garage will be able to perform a 'sniff' test to check for combustion gases in the coolant, as the lack of oil/water mixing does not necassarily mean the HG is OK.