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Article posted: 10/14/2012 5:19 AM

Engine oil vapor may cause problem

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By Doug McAllister

Q. I own a 2008 GMC Acadia with a 3.6-liter engine. My mechanic noticed oil pooled underneath the air filter. He told me it appeared to come up the air intake hose from the engine to the air filter. He is regularly in touch with other independent shops and the word is this problem exists and in some cases has led to costly repairs.

He suggests I get GM to fix it while it's still under warranty or sell the car. After inspection at the GM dealer I was told by them everything is fine and it was by design that oil might pool there. I asked, "You mean GM has designed an engine where oil travels up a tube whose purpose is to deliver air to the engine? What is the recommended maintenance procedure as oil pools?" They really did not have a response other than to say it was the design and should I experience any further problems to bring it in.

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The warranty expires within a year. I'm uncomfortable keeping the car not knowing if GM will stand behind it post warranty. Any ideas?

A. Thanks for a great question. I am not sure I am going to be able to shed anymore light on this issue from what you already know. What I have been able to find out from the GMC dealer we use, is this is a condition that is common with most of these cars and it seems to have to do with the way the crankcase vapors are scavenged off the engine.

This is typically known as the PCV system. A long time ago automobiles used to just vent the crankcase vapors into the atmosphere -- we're talking in the 1960s and prior. Then they came up with a way of routing those vapors back into the intake to be burned.

With your car, these vapors are being routed into the air intake nozzle and some of the oil vapor is pooling in the air tube. I do not necessarily think it is indicative of a major problem, rather a poor design on the PCV system. The problem that potentially could arise is too much oil builds up and it may coat the Mass Air Flow sensor with an oil film, causing a running problem or a failed sensor.

This could be avoided by cleaning that tube out at every oil change. At this point I do not see that GM is admitting to a problem; there are no TSBs (technical service bulletins) or recalls on this issue at all. I hope this helps and thanks again for the question.

Q. I think I wrote to you about this problem, but I do not remember the answer. When my car is at operating temperature and at a complete stop, I can see the passenger seat-belt buckle vibrating. There are no warning lights coming on. Also when I put a plastic bag on the passenger seat I can also see the bag vibrate.

What could be causing this? Have you been in a 2006 Pontiac G6 GT Coupe with the 3.5-liter, 201-horsepower engine? Can you tell me if this is normal or do you think it has something to do with one of the engine mounts not being positioned right.

The reason I say that is because I had a 1993 Chevrolet Cavalier. After the head gasket was replaced, there was so much vibration in the car that I took it back to the dealer who determined the engine mount was not positioned right after the repair. That's why I am wondering about this vibration being related to the engine mount.

A. If memory serves me correct you have somewhere around 60,000 miles on your G6? Did you have any work done recently that would have had an effect on the engine mounts?

Typically a motor mount would not shift on its own and your car is new enough that I would not suspect a bad motor mount, but anything is possible. Have your technician drive the car with you and I believe he could determine pretty quickly if you have anything going on that should be investigated further.

As always follow the maintenance schedule that is outlined in the owners manual and use a top-tier fuel. Gas station chains that sell top-tier fuel in all octanes are listed at www.toptiergas.com. If you have not been using a top-tier fuel, you may want to consider a fuel-injection service. I hope this helps.

• Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 123 Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.

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