Thermostat leak!!

[Eriedor]

Disaster strikes my rebuild, filling with coolant and I discover a persistent leak from thermostat housing to block (k series).

I fit a new thermostat so it's clearly related. The question I have is how much of these black seal remnants should I be cleaning up before fit? (or has a previous person put sealant here??) There's some on the outer edge and inner edge, do I completely clean up both? It's quite hard to get it off so first time round I scrubbed it until it felt smoothish and then installed the new thermostat - to disastrous results....

[Wrightpayne]

It needs removing. The plastic t stat housing should have an O ring present and with a bit of rubber grease (to aid installation) should be all thats needed to seal it.

[Wrightpayne]

Part number for the o ring CDU 3858 L

[aerobod - near CYYC]

Also, best to use a combination of gasket softening chemical and a plastic scraper with minimal usage of a Scotchbrite pad to remove any gasket material, to avoid any rounding off of the housings.

[revilla]

Agree with all of the above. There should not be any silicone used there. If when you remove the silicone you find corrosion pitting (maybe why silicone was used in the first place?) you may need to be a little more aggressive polishing itnout with red grade Scotch Brite.

Are you absolutely sure the leak was from where the housing enters the block? One other thing to watch. Well two or three actually, I keep thinking of more ...

1) Make sure the plastic thermostat housing isn't cracked.

2) When you fit the housing to the block, using the correct O-ring and a little silicone grease and after cleaning up as described above, wiggle it in gently with a circular motion to make sure the O-ring doesn't get pinched and seats properly.

3) Make sure the seal that goes around the thermostat itself is correct. I've seen aftermarket ones that are too thin. Sometimes the thermostats come with a set of generic seals and the one that looks right in the set usually isn't, it's too thin again. When you put the two halves of the housing together, they should a millimetre or two apart and the tightening of the screws compresses the seal. If they're too thick however, the housing bows out along the sides with a gap between the two halves, and leaks again. Get a proper OEM seal from Rimmer or similar.

4) Don't push the hoses too far onto the housing. The housing often has some triangular plastic reinforcement fillets, if you push the hose on far enough to overlap those it pushes the house outwards away from round portion and gives you a hefty leak.

 

[Eriedor]

Thanks all for the comments. I'm 90% certain it was the thermostat -> block, I've cleaned it out now with a scotchbrite and quite a bit of persistence and it's so much better. Fingers crossed it holds when I refill in the morning. I got the thermostat housing brand new including the thermostat from dmgrs.co.uk so I assume the housing is sealed ok.

[SM25T]

Have you drilled a hole in the top part of the thermostat baseplate to allow air to pass through ?