Should I coat the head gasket with something before I replace it or should I put it on dry?
Very often they just go on dry on modern cars. What kinda car?
I’ve always seen them go on dry. I’d need it in writing from an authority like the carmaker (factory service manual) to do otherwise.
If you have an aluminum head and iron block, I think that using anything that would cause the gasket to stick will eventually cause it to fail, or so I’ve been told. I always go dry.
Check to see if the head bolts are reuseable or if they have to be replaced. If the headbolts have belleville (belvil) washers under them, they have to be replaced.
Check with the factory service manual for whatever vehicle you are working on. Cleanliness is always important. For many applications, Permatex copper gasket sealant in an aerosol can is not a bad idea and is popular in iron block/aluminum head applications. My brother recently used it on his 22R-E at the advice of the folks on his Toyota forums. New head bolts are always a good idea and mandatory in many applications. Torque wrench is a must in all cases. Harbor Freight has nice ones that work very well for $10-15 with a coupon.
The head gasket set will come with any sealer/lubricant that should be applied before installing the head gasket.
If it’s not included, don’t use it.
I’ve always used aerosol Copper Coat on applications with aluminum heads or all aluminum construction based on service school instructions so it’s a habit I’ve always stuck with.
There’s never been a downside or problem due to the use of CC.