Valve Stem Seals and Valve Guides

General Information

"My car makes a big puff of smoke when it first starts up."

Presuming that you have no external leaks, that the engine is still burning oil, and that the trouble was not temporarily caused by a sticky oil control ring (which can happen on a car that's sat for some time), this is usually due to bad valve stem seals, worn valve guides, or both. Some of the oil that has collected in the head drains into the cylinders past the broken seals and/or worn guides after the car has been shut off. This also happens when decellerating and in high rpm, high vacuum, low throttle position situations like highway driving as oil gets sucked past the seals and guides due to high cylinder/manifold vacuum. Conversely, since city driving is fairly low rpm, high acceleration, the engine spends more time in low vacuum states; reducing oil consumption from bad valve stems seals or guides.

This is a pretty common occurance for Chevrolet engines after 80-90k miles and can often be cured by replacement of just the valve stem seals. An air compressor, a special hose that fits into the spark plug holes, and a valve spring compressor are the special tools required to do this job. If these tools and a little mechanical expertise are available to you, the job is pretty cheap and easy to do -- around $50; although some danger of stepping on a "near and dear bodily part" exists in dropping a valve into the engine; which would force you into removing the offending member . . ahhh... I mean head . . ahhh... I mean *cylinder* head and would make this job MUCH more painful . . . ahhh... I mean difficult. Also, VERY IMPORTANT, make sure that the radiator cap is off since there is a possibility of a blown headgasket causing this oil burning and you wouldn't want to pay for a radiator too. . . :)

There are other causes, of course. Blown head gaskets, cracked or warped heads, and cracked blocks can all be responsible for this type of oil consumption. Worn rings, however, will usually show up in a blue haze coming from the exhaust on *acceleration* and/or high 4k+ rpm engine speeds (above typical US highway norms for a Fiero), which may or may not be visible from the driver's seat. Best to have someone follow you and see if there's a cloud being left behind and what conditions make it happen.

If the valve guides are worn, the only remedy is a valve job. Replacement of the seals won't help and nothing in a can is going to make any difference either. Also, be aware, that if you do a valve job on an old engine, it's possible that the car will actually use *more* oil than it previously did, since the valves are now sealed enough to make the worn piston rings pass oil. This has happened to me more than once -- although not on my Fiero.

At 86k, my V6 is starting to smoke a little on cold startup, so I'm planning to do my seals soon -- although I'm still not using any appreciable oil at this point; less than 1/8 qt between changes every 5k miles (Mobil 1, Fram filters, no leaks allowed).

In a nutshell, have someone follow you under accel and decell conditions. If the smoke is *not* visible or only momentarily visible on acceleration, try the valve stem seals. It's fairly cheap (even if done by a professional) and will tell you if you need to dig out the lint in your wallet for something more extensive. Could be it's time for the 3.1L crank/piston upgrade, but let's hope you don't have to do it unless you want to!

From: Mark Madden

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