If both surfaces are clean and flat and you are using a new gasket, no sealant is necessary.
Follow the upper radiator coolant hose and where it meets the engine the thermostat is under the little neck. It should be 2 or 3 bolts to remove it make sure to se a new gasket and put the new thermostat in the right way and use sealant on the gasket as well as the bolt threads. Make sure to put the sealant on the INSIDE of the bolt holes on the gasket not all the way around them or it might leak. Also don't use 4 lbs of sealant for one gasket
no gasket sealant needed. Just original gasket is fine.
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In most cases a new gasket is required, but no sealant.
you mean like k seal?, there only temp fix if that, the gasket should always be replaced if its failed
You need the sealant on the ends where the supplied gaskets don't cover fully.
never
Depending on the exact engine there may be a gasket for it. If not it may be a sealant like gasket goo. -I am unclear on that term 'cylinder jog'. but most crankshaft bearing surfaces should have a gasket, rather than a sealant.
Probably your cam cover gasket (top of engine)leaking into the wells. You can use sealant instead of gasket
When using a new pan gasket, no sealant is necessary. Using sealant on a automatic transmission pan gasket is a bad idea, excess sealant can cause trouble.
you should never use a sealant on a head gasket as that is only a temporary fix in an emergency situation. The only permanent fix is to replace the gasket.
Never use sealant for a head gasket! It is used as a quick fix for cracks in the gasket but will not last very long. Safer to get the job done correctly.