A diagnostic test on the Ranger showed that it needed a new thermostat. I've ordered an OE Motorcraft which comes with gasket. Does the gasket go on dry or does it required any sort of sealant?
I think it's more of a preference thing, a small amount of sealant wouldn't hurt. The housing on my S10 only really requires the o-ring gasket on the thermostat itself. I applied a small amount of Permatex sealant on the housing just for piece of mind.
I've used gasket tack only to hold it in place while the bolts are fitted - this usually applies for vertical surfaces (rear diifs, waterpumps, etc.). If the mating surfaces are horizontal, I don't bother with extra stuff...