Why does your Volvo give off a bluish smoke when you let off the gas?

Answer 1

A quick guess is that the valve seals are worn and/or maybe the valve guides. Oil is pumped up over the top of the head to lubricate the valves. The valves allow the engine to "breathe" by letting the fuel-air mixture into the cylinders (or just the air in fuel injected models) and by letting the exhaust gas out. The cam shaft operates the valves either directly or indirectly, depending on the engine design. The whole thing needs to be lubricated with oil to keep it moving freely. Valve seals seal the stem of the valve and the head to prevent oil from going down along the guide and valve stem into the intake port. When you let off the gas, the intake manifold vacuum goes up, and this "sucks" oil past worn valve seals and along worn valve guides into the intake manifold where it's sucked into the cylinders and burned. Oil burns "bluish" under these circumstances. It is possible to replace just the seals, but it's tricky. What's the wear on the guide like? It may be time for a valve job. The head(s) is (are) pulled and disassembled so the guides can be refurbished or replaced and the valves and seats can be reground. When the head is reassembled at the machine shop, new valve seals will be put on. (They almost always come in the head gasket kit.) A link is provided to a picture of a valve assembly.