This may be a stupid question but do you use the gasket dry or do you use it with some kind of sealer? I've been told both ways and I'm not sure which way is correct. The things I've read say to refit in the reverse order which doesn't really help.
I always do them dry. I have pulled off a number that also had sealant on them, which imo looks bad if it's not cleaned up around the edges. I had a cork gasket that leaked after installation, and I suppose that would have been a good time to use sealant, but I tossed it in the trash and used a different gasket.
I think with the newer thick cardboard style, the use of sealant is no longer needed. The older very thin paper gaskets, perhaps, benefited from the use of sealant.
I also install them dry, and make sure the head is dry as well as the aluminium thermostat housing face. Only once did I ever have a leak, and that was a cork or cork composite looking gasket which I think I crushed by over-tightening.
I always glue it to the thermostat housing aluminum and coat the other side with grease, that way when I swap thermostats for the season, I can reuse the gasket.
I do the valve cover gasket the same way, I've never had a leak on either.
Now why didn't I think of that!
I've always used some sort of RTV on the valve cover, and after 15 years use, only changed the gasket last year. Thermostat gaskets are a whole other matter, though. I normally have a small stack of 6-8 pieces at any given time, because I go through them like water.
Thanks for the great (though obvious) tip!
............old guy tricks..... ;D