Have a 390 Fe Motor with a road draft tube (no PCV). When I bought the car, it ran great. No smoke. I took it in to a shop for oil change and to have some of the leaks fixed. Got it back after oil changed to synthetic with oil stabilizer and the valve cover gaskets replaced. Once it warmed up there was a moderate amount of smoke coming from the roaddraft tube. Also some steady dripping of oil. Another visit to shop and an intake manifold gasket took care of the drip (still a few leaks I think rear main). However the smoke from road draft tube is still present once the car warms up. Seems to be heavier the warmer the engine is or longer it runs. Some also from oil breather at front of intake manifold. My question is could an different oil cause this smoke issue? Odd it didn't smoke at all previously and I drove it 35 mins in high 80s weather. Your advice/experience is welcome!