Issues sealing a thermostat housing on my 5
Discussion
on a 1.8 mk1. After the waterpump failing & have just done the cambelt, pump & stat. The stat didn't come with a gasket so I have tried the red & blue types of hardening instant gasket and despite following the instructions both types have leaked. Bloody stat didn't come with a paper type gasket. Sooooo, have I got a slightly warped stat housing that just needs a paper type gasket making up or had my head gasket gone? Worryingly when it got hot no water seemed to come out of the pump, although it didnt boil dry it was missing about a litre of water.
I tore my gasket when I removed the housing, I patched it up with something called "Fernox LSX", its a silicone based plumbing bodging paste. It held for long enough until I could buy a new gasket.
You need to remove every trace of gasket from both faces of the housing though, mine had a little drip when I first assembled it, but I think a few hot and cold cycles have sealed it up now.
You need to remove every trace of gasket from both faces of the housing though, mine had a little drip when I first assembled it, but I think a few hot and cold cycles have sealed it up now.
When I last did the thermostat I had the housing unbolted and ran it around on a piece of wet and dry for a while until it was totally flat and smooth, and did the same with the cap. The only time I've had a gasket leak is when I've had sealant on it, so since then I've never used any sealant, just the paper gasket, and made sure both faces are really clean and smooth.
Do yourself a favour and get hold of some gasket paper - it's cheap and always handy to have around... if you can't find it locally there's plenty on Ebay. Don't concern yourself too much over what thickness to buy just go for an intermediate and you can press it into use on all sorts of jobs. To cut the gasket hold the paper tightly over the casing to be fitted and tap around the edges with a hammer, the edge of the casing should cut through the paper; for any bolt holes either use the rounded end of a ball pein hammer or use a more suitably sized dome headed nut or bolt tapped into the bolt hole. Hope that all makes sense, if not I'd imagine there are guides on the 'net.
Whether using paper or silicone type gaskets make sure both surfaces are thoroughly clean, an old chisel with the end ground square is ideal for a scraper, a plate of glass and a sheet of wet and dry is ideal for flatting a casing to make sure it is not warped - lay the wet and dry on the glass and rub the casing over it until the mating surface is a consistent finish all the way round (not always possible with odd shaped casings unfortunately), sometimes it may be easier to use the wet and dry wrapped around a small wooden block or similar, do not use it without some form of support or you'll end up doing as much damage as good.
It's not a good idea to use sealants designed for other purposes on cars if you are not certain of their content. Some plumbing sealants for example may contain an acidic element (which can be useful), others may fall to bits and get washed around the inside of the cooling system and never use unsuitable sealants for anything fuel related.
Whether using paper or silicone type gaskets make sure both surfaces are thoroughly clean, an old chisel with the end ground square is ideal for a scraper, a plate of glass and a sheet of wet and dry is ideal for flatting a casing to make sure it is not warped - lay the wet and dry on the glass and rub the casing over it until the mating surface is a consistent finish all the way round (not always possible with odd shaped casings unfortunately), sometimes it may be easier to use the wet and dry wrapped around a small wooden block or similar, do not use it without some form of support or you'll end up doing as much damage as good.
It's not a good idea to use sealants designed for other purposes on cars if you are not certain of their content. Some plumbing sealants for example may contain an acidic element (which can be useful), others may fall to bits and get washed around the inside of the cooling system and never use unsuitable sealants for anything fuel related.
Edited by spoodler on Monday 7th October 13:00
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