Blue-White Smoke/Exhaust Farts

[Davey G]

Ok, after getting the suspension redone (fabulous) I am noticing a thin bluish-white smoke coming from the exhaust when accelerating (friend was driving with me following). Also when decelerating there is a small backfire/fart sound. The tailpipe also looks oily/sooty. It runs/idles well. What's going on?

[Zs-ondabrain]

Sounds like blow-by. Blue/white smoke is typically Oil. Could be rings, valve seats or guides. The back-firing sound like it's dumping fuel and igniting it on decelleration. Typical of SU's but not sure on FI motors.

Dave

[70 Cam Guy]

A bluish-gray smoke is usually oil smoke. There are indicators of where to start depending on when it smokes.

smoke on cold start but dissipates: indicative of worn valve seals. oil settles around the valve seals and seeps past the seal. It burns at first start and is usually fine after

smoke on accel or under load: this points to blow-by, bad oil rings like Dave said

oil smoke on decel: this can point to worn valve guides. Closed throttle, high vacuum pulls the oil past the seals/guides and burns the oil

I'm not too familiar with the FI cars but I've heard they are pretty 'dirty' on decel so this could be unburned fuel pops you're hearing. If you have exhaust leaks, you can get the pops and backfires too

[Davey G]

A bluish-gray smoke is usually oil smoke. There are indicators of where to start depending on when it smokes...

I'm not too familiar with the FI cars but I've heard they are pretty 'dirty' on decel so this could be unburned fuel pops you're hearing. If you have exhaust leaks, you can get the pops and backfires too

The top end was less than 15,000 miles back (head still shiny and no gasket leaks), though I did not own the car when it was done, so who knows how it was done. I can pull the valve cover for an inspection of valves, etc. But, I do have a small exhaust leak up by the manifold that needs fixing. I'll let you know what I find out.

[Davey G]

Also noticed that the oil level looked like it was about 1/4 quart past full. Noticed in the manual that 4 3/4 quart was how much to put in. Would the extra 1/4 quart cause the blow-by?

[70 Cam Guy]

The top end was less than 15,000 miles back (head still shiny and no gasket leaks), though I did not own the car when it was done, so who knows how it was done. I can pull the valve cover for an inspection of valves, etc. But, I do have a small exhaust leak up by the manifold that needs fixing. I'll let you know what I find out.

You are right, without the paperwork it's hard to know exactly what was done when the head was done. I would probably give them the benefit of the doubt though if a decent machine shop did the work.

I can tell you I've been dealing with my header collector bolts loosening the last couple weeks and I can tell when they start getting loose because the pops get way more pronounced/louder on down shift and decel. What I need is some better lock washers :stupid:

When my header gasket was leaking bad, that thing would back fire and people would duck! (not really but it would be damn loud)

I know Porsche 911's will smoke like a chimney if you overfill them but I am not sure about our cars. My gut feeling is that a 1/4 quart is not significant enough to cause smoking.

I am somewhat curious how the compression is and the condition of your PCV valve. When the PCV valve is clogged on some cars, the excess crankcase pressure can cause some different things like oil seal seepage and maybe smoking. This may apply more to newer cars though

Edited March 21, 2010 by 70 Cam Guy

[Diseazd]

White smoke is H2O........Usually doesn't happen till engine warms up. Start the car check for smoke at idle.....if it gets worse after thermostat opens and car is at operating temp it could be a leak. Aluminum Z heads (40 years old )can be corroded around water passages. Eliminate one thing at at time. If it smokes right away I agree with Andy. If it smokes all the time I agree with Dave.

[Davey G]

The smoke seems to have cleared up for the most part now that the oil level is down to the "full" mark rather than 1/4 quart over. The car is running better today. I found the grounding wire from the AFM was not reconnected after replacing it :stupid:. Seems to have leaned out a bit, reving smoother.

Took a trip from Houston to Galveston and back today...60 degrees...sunny...lower humidity, including Ben-N-Jerry's on the seawall. All-in-all a good Z day. I drove it hard and the car did not complain.

Planning to get the weatherstripping on this week, which should cut down the wind noise some.