Periodic bloom of smoke from exhaust only when cruising
 

About a week ago, I bought a 2006 SAAB 9-7X (Trailblazer) with the 5.3L V8. I've been driving it around town with no issues. The engine has plenty of power and idles smooth.

BUT, I took it on a 4 hour drive out of town and noticed that while cruising at 70mph, I could see in the rear view mirror an occasional bloom of smoke that lasts but for a second or two. It seems to occur every 15 to 20 miles of driving. There's no noticeable loss in power when it occurs. It was drizzling rain most of the way and at first, I thought what I saw was water being kicked up by the rear tires, but the smoking continued when I got to dryer roadways.

I checked the oil when I got home and found it to be a half quart low, but I'm not 100% sure it was full when I left on the 8-hour round trip.

I'm thinking PCV or EGR but never heard of either of these causing a periodic issue like this. Anyone have ideas on this problem?

smoke is some kind of oil or coolant in the cylinder. the castech heads are a common problem to crack and let oil or coolant in.

#06-06-01-019B: Information on Gradual Coolant Loss
Over Time with No Evidence of Leak Found - (Jun 12,
2007)

2004-2006 Buick Rainier
2001-2006 Cadillac Escalade Models
2001-2006 Chevrolet Avalanche, Blazer, Silverado, S
uburban, Tahoe,
TrailBlazer Models
2001-2006 GMC Envoy, Jimmy, Sierra, Yukon Models
2001-2004 Oldsmobile Bravada
2005-2006 Saab 9-7X
with 4.8L or 5.3L VORTEC® GEN III, GEN IV V8 Engine
(VINs V, T, M, B, Z -
- RPOs LR4, LM7, LH6, L33, L59


http://ww2.justanswer.com/uploads/Bl...t_loss_5.3.pdf

Thanks for that information. I haven't seen any coolant loss, but may have seen oil loss. The weird thing is that it never smokes at start-up or idle or "around-town" driving conditions. It only happens in bursts every once in a while when cruising down the highway. Do you think leaks in the head would cause this?

in order for there to be smoke in the exhaust there has to be oil or coolant in the cylinder. that engine doesnt have either in the intake manifold so that only leaves some thing like head gasket, rings, or that cracked head. but the head gasket and rings are not common on a newer LS engine and the cracked heads are.

White smoke (coolant) or blue smoke (oil)?