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MG MGB Technical - Thermostat housing gasket

I was suplied a thin cork thermostat gasket that after fitting leaked up past the stud and out from under the nut once the water had got hot.Tightening the nut made the leak worse, plus the cork just spewed out from under the housing. I probably over tightened the housing but it did not feel like it at the time.
If I recall correctly, l had the same problem 3 years ago with a cork gasket and I had to make a thin card one.
Is it the norm to have a cork gasket under the thermo. housing. Trev
Trevor Harvey

Yes, and it is the norm that people overtighten them.

Water also leaks up from the threads of the studs - at least two are in holes drilled right through to the water jacket.

Fit studs with a little loctite to seal the threads. Lightly coat the cork gasket with Hylomar both sides and
fit with nyloc nuts - not spring washers, tighten just enough to compress the gasket slightly - it should NOT bulge out!
Chris at Octarine Services

if your studs are anything like mine then the nuts only just fit on top of the housing so need a thin gasket

I've got spare thin paper gaskets I can put in the post to you but I'd recommend using the Klingersil gasket, I've only got one of those and it's fitted on the car

I'm sure you can get them elsewhere but I got mine from T*ss -

Nigel Atkins

I use Klingersil ones, no problem with leaks.
Brian Shaw

Overtightening the thermostat housing nuts bows the housing cover. In the past I've had to spend some time flattening it again rubbing it on a sheet of wet and dry laying on a flat surface like a sheet of glass. When you start it's obvious if it is bowed as the parts on the outside of the stud holes shine straight away, whereas in between them doesn't until it is flat.
Paul Hunt

Also, when fitting the thermostat housing, don't forget to coat the studs with plenty of antiseeze. If you fail to do this, the next time you try to remove the housing, it will be corroded to the studs and will take a lot of effort to dislodge it. RAY
rjm RAY

I have ordered some of these Klingersil gaskets and am awaiting delivery. Took the housing off, the stud the leak is coming from is the one that does not go through to the water jacket. Attempted to remove them to put sealant on the threads but could not get them to move and as I have only just put the engine back together, I don't want to shear one of them.
On examination of the housing, corrosion has occurred on the thin strip of metal on the inside of the stud hole where the leak has been coming from, this is no doubt what is the cause of the problem. About half an hours flattening has got a good surface all over the cover. I have not looked that closely at the housing before and there is very little metal between the stud holes and where the thermostat sits, not much more than a millimetre, so it is not surprising that leaks occur there.
Thanks for the advice. Trev
Trevor Harvey

Trvor is your thermostat housing made from aluminium, if so the housing on USA spec 1974.5 engines have a cast iron housing, if you can scrounge one from our american cousins then that would sort out your leak problems. I know its a long shot but I imagine getting hold of a decent Alloy one is getting more difficult.

john wright

John, the aluminum thermostat housings are still in production and cost less than $15. RAY
rjm RAY

The housing I have is either cast iron or cast steel and is showing a fair bit of corrosion on the inside.
John, are you reccomending the aluminium ones. Now that I have ground the mating surface, and with the other gasket, I am hoping it will sort the leak. Trev
Trevor Harvey

Hello Trevor, I am recommending the cast iron one. Corrosion shouldn't be an issue with the CI unit. The only downside if the mating surface is not in good condition it will take longer to get a flat surface.

john wright

An 'Old Skool' tip.
To restore the face of an alloy thermostat housing.
Find a paving slab that is not too course, or a patio paving stone. Wet the stone with some water as a lube.
Place the thermostat housing face on the slab and applying light pressure move it around in a figure of eight. It will refresh the surface and give a good surface for the gasket to bear upon.
Alan Anstead

The klingersil gasket works a treat. Far better than the rubbish cork ones.
Trevor Harvey

good, glad to hear it

tbh it was only after I posted I realised that this was the B and not the Spridget forum but it's the same gasket
Nigel Atkins

I put a new gasket in after replacing the thermostat. It was a paper type, not cork. I applied some Permatex sealant to both surfaces (I had some from when I reinstalled the fuel gauge sender in the tank).
It sealed fine.
Then, I had to remove the housing as the spigot had corroded and it was too hard to get a good seal where the radiator hose attached.

I used the same seal with the new allow housing and again, it has sealed well with no sign of leakage.

John Minchin

This thread was discussed between 17/12/2013 and 01/01/2014

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