How to diagnose head gasket? Valve guides? Bad turbo? when you’re seeing white smoke in exhaust. Today we look at how to diagnose white smoke when decelerating from a 2002 XC70.
MVS Volvo Forums member 1bigb1:
Need some advice ,do I look at my Turbo OR do I look at my Head ?
I have a Volvo v70xc AWD Auto 2002 ,When Driving normally I do not have Smoke coming from exhaust ,But when I accelerate Hard and then Release / decelerate , my foot from fuel then I see white smoke coming from my exhaust ..
I did a test today if I Accelerate 50% of throttle and then decelerate the amount of smoke from the exhaust is allot ,But if I accelerate 100 % and then decelerate the amount of smoke is much less …any more ideas ?
MVS Contributor Botbasher:
Could be either one. You didn’t mention how many miles on the car?
Smoke on decel is usually from valve guides in a non-turbo car (Accel smoke is rings, decel smoke is guides) The vacuum in the manifold pulls oil past the guides and burns it.
When you have a turbo, you also have the turbo bearings that can leak oil into the intake track under similar conditions. A little is somewhat normal, but enough to smoke is not.
You may be able to differentiate between them by opening up the intake just before the inter-cooler and see how much oil is there. Mine, an 03 with 60k on the motor, has a slick of oil in the pipes, but nothing that will drip and easily wiped off the inside of the pipe.
If you find it relatively clean in there, then the guides would be suspect, but not a sure thing. To dig deeper if needed, I would drop the exhaust down-pipe before hanging any one criminal. 3 nuts and you’ll be able to manipulate the shaft with your fingers. Move it side to side and in and out. You should have some side to side and next to nothing for in/out.
This would be my suspect… oil on the back side of the compressor wheel, being atomized in the intake track after a hard accel (high oil pressure). A slightly thicker oil next change can help tell you if it’s simple wear (bearings or guides) or a bigger failure pending but it’s only a mask for the inevitable failure.