3.8L lumina Ltz smoking.

[fons]

My 98 chevy lumina LTZ 3.8L ,with 246000km,is smoking alot from the exhaust.The colour of the smoke looks normal,but a mechanic told me it smelled of oil not coolent. When i asked what it could be the cause.He said it would be costly to diagnose and repair. The smoke is more obvious when starting ,and especially when the engine had been running for a while and shut off, then started again.A big cloud of smoke is let out . But when driving away, and when idling at a stop the smoke is less odvious. I have'nt noticed any coolent loss, but have noticed oil loss at about a half quart to a quart every 2000 km. The car also has a problem with the Evap vent system. When the car is running the gas tank will collapse in ward with pressure ,and when i remove the gas cap the pressure is released. Can the Evap system cause the smoke from the exhaust? Or has any one else had a similar problems or any ideas of what can cause the smoke.

[jeffcoslacker]

What you are describing sounds like oil smoke from worn valve guides/seals.

That oil comes from above the cylinder, and leaks past the affected valve into the cylinder as the car sits parked. When you start the engine you get an initial blast of smoke that dissipates as it runs.

Uusually worn guides/seals will give you a little blast of smoke after idling for a bit (like at a stop light) or when taking off after coasting down from speed with the throttle closed....both are high vacuum condtions, which actively sucks oil past the defect into the cylinder...where it burns off suddenly when the throttle is opened up again.

Faulty rings and worn cylinders tend to smoke under low vacuum/higher rpm as more oil pressure is delivered to the cylinder walls, like when accelerating hard, and do not accumulate oil in the cylinders while sitting.

So I think it's safe to say the problem is in the top end...but has nothing to do with the fuel vent problem. That's hard on your fuel pump however...

If you want to identify the problem cylinder(s), let the car sit overnight, then disable the ignition and crank the motor just a couple of turns, then pull the plugs out and see which are wet with oil.

A bad seal can be repaired with the engine intact, but requires some special tools...worn guides require the head to be removed and sent to a machine shop for replacement.

Just to cover all your bases, check the breather side of the PCV system for blockage too, that can blow a lot of oil back into the intake, but you generally won't see smoke from it, just abnormal oil loss and sometimes a saturated air filter, depending on the design...

[fons]

Thanks for your reply. I failed to mention the strange whinning sound coming from the engine. It sound like it's coming from the drive belt area. So i removed the belt and the noise was still there. The sound also seems to be coming from the bottom end of the engine and became louder when i pulled on the throttle wire. Do you think it could be a worn bearing that is causing the noise and the smoke? or to separate problems.

[jeffcoslacker]

Wow you have a lotta demons huh?

Bottom end bearings knock and rattle, not whine. A bad bearing won't directly cause smoke. The only other items turning in that area without the belt is the timing chain and related components...but they usually make fluttering rattles when bad...

Sometimes tranny noises will transmit through the crank and seem to come from the front of the motor, like a torque convertor or tranny pump howl...but if you get under it or listen close to the bellhousing area it will be more prominent there.

Take a broom handle or something similar and use it like a stethescope, putting one end on the motor and the other very close to your ear...it works well and you can find the source of internal noises pretty easy.

***Hey...check your tranny fluid....If your car uses a vacuum modulator for shift control, it might be sucking tranny fluid into the motor and burning it...the pattern of smoke mimics valve seal smoke (inhales under high vacuum conditions, smokes when you first gas it)...the whine might be from the tranny fluid low...

Just a thought...tranny fluid burns white, oil blue...you said the color is more like normal exhaust condensate vapor, yes? Maybe this is your answer...that would be nice, it's an easy fix...I can fill you in on what to do if that's the case...

[fons]

Thanks again.Today i took my car to a tranny shop, that a friend recommend. The mechanic diagnosed the problem by separating the flywheel from the tranny. Then ran the car and the noise was still there. I got a better listen to the noise and it now sounds more like a rattle, that flutters .Hard to describe. But it's not the tranny. I'm thinking more in the line of a bad bearing or chain as you described. Sound costly and not worth repairing? on a car that not worth much.

[Bearwulf]

Simple thing like a stuck or clogged PCV valve could cause the smoking & oil smell in the exhaust.

[fons]

I checked the PCV valve. Looked good ,but replaced anyway .No change,still smoking.

[jeffcoslacker]

Pull the vacuum hose off the modulator valve and see if it has fluid in it...

[fons]

I can't locate the modulator valve. I looked in my hanes manual, and where it says it should be on the rad side under the exhaust crossover pipe. I also removed the air filter box, looked every where and can't find it. Am i looking in the wrong place?

[jeffcoslacker]

It's down pretty low, near the pan on the tranny. Has a steel line coming off of it that runs up to the back (driver's side) of the intake manifold...

there's a chance yours doesn't use one. Looks like this...

[fons]

My Lumina has a 4T65E tranny .I found out in 1998 they switched from a vacuum modulator to electronic. Another thing i have also noticed my gas tank is now building up pressure in the tank when the engine is shut off. Before i would release the gas cap to release the pressure, and it wouldn't build up till i started the engine. Now it's also happening when off?

[jeffcoslacker]

pressure in the tank will change a lot with temperature outside if the vent system is not open...