My '03 wagon stinks of burning oil but only when first warming up and only in the winter when temps are below freezing. It takes 4 minutes of driving before the car's heater blows warm and then the stink comes in from the engine bay thru the heater vents. But after another couple minutes it stops and doesn't smell at all until after the next cold start. So I'm thinking maybe it has something to do with a warm engine expanding some part. But it doesn't smell when the engine is cold and it doesn't smell after fully warmed up. It only smells when partially warmed up. The car doesn't use much oil at all and never needs any added between changes. Ideas?