I had to remove the Manifolds over the weekend to replace a broken exhaust stud. The tail pipe wasn’t connected properly and all the exhaust was going into the cab, I also replaced the thermostat for the hell of it.

Anyhow I was running the engine to warm it up (with out the radiator cap) and now that the tail pipe to flange is sealed I notice a little smoke coming out of the valve cover oil filler cap. It wasn’t a lot but it was enough to notice it faintly in the sun light glare.

What causes this? Excessive gas vapors? Or is this normal? New manifold gasket?

Thanks
Billy