Weak valve seals or guides?

Wobdog

Wobdog

a.k.a Mike
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My Daughter in law got me for Christmas "The best of Hack the Mechanic by Rob Siegal. In a section about how he test cars before buys them he uses this test:


Accelerate to 2500 rpm in 2nd gear then back off the gas and let the engine coast all the way back down to 2500 rpm. If he sees oil smoke during this powered deceleration the valve seals and or guides are weak. When I performed this test myself I get a massive amount of oil smoke. Is this a sign that I have weak valve or seals or guides? Should I do anything? The car runs great, does not burn oil and also has no blue or any spoke when I start it. It purported has 135,000 on the original engine. Love to hear the forums thoughts
 
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You mean accelerate to 5000rpm then back off. Yes, it is a good test and means valve stem seals, valve guides themselves are pretty sturdy.
 
Yes Take it to almost redline, then let off gas. Lots of smoke out of exhaust. Should I be concerned?
 
Perfect that is what I needed to know. Always trying to learn! I have a LONG ways to go.
 
If it is the valve stem seals, it will also smoke if it idles for a long time (~5-10 min) when warm. This usually happens when the valve stem seals wear out or dry out. Either way, it allows oil to drip down the stems into the combustion chamber, making that smoke. The newer N62s also have this major problem, exacerbated by the hot-vee turbo setup. The thinking is the heat dries out the stem seals. My local indy suggested using a specific Liqui-Moly fluid to help with this problem based on his experiences with N62 valve stem replacements. (this stuff: https://www.amazon.com/gp/product/B00CPL8WY8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)

It worked for me, but I am also planning on replacing my engine. I figured I had nothing to lose.
 
With bad valve guides or seals, the pistons will pull oil down the intake valve stems on the intake stroke at high vacuum conditions. This would be idle, steady state cruise, and most of all, with a trailing throttle. Try a closed throttle and a long downhill for the biggest effect. Even when you can't see the smoke out the rear view mirror, the car behind you can. You are definitely burning oil. That's what that blue smoke is. If you don't drive the car much, it won't show up as oil consumption. Pull the plugs they more than likely won't have that nice, light brown deposit on them.
 
Wobdog said:
My Daughter in law got me for Christmas "The best of Hack the Mechanic by Rob Siegal. In a section about how he test cars before buys them he uses this test:


Accelerate to 2500 rpm in 2nd gear then back off the gas and let the engine coast all the way back down to 2500 rpm. If he sees oil smoke during this powered deceleration the valve seals and or guides are weak. When I performed this test myself I get a massive amount of oil smoke. Is this a sign that I have weak valve or seals or guides? Should I do anything? The car runs great, does not burn oil and also has no blue or any spoke when I start it. It purported has 135,000 on the original engine. Love to hear the forums thoughts
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As a corollary to the posted suggestions, thinned, contaminated or lighter viscosity oil can exacerbate valve stem/ valve seal problems. This may be particularly true with higher mileage and marginally maintained engines. For new valve stems and valve guides to function properly usually requires valves with unworn valve stems. The latter may be the hardiest parts of the bunch, but they do not last indefinitely. When performing any valve service with the cylinder head removed, guides and corresponding valves should be examined for wear.

Unless you know what oil is currently feeding the engine, and that it is leaning toward a heavier viscosity (e.g., 20W50), I would consider changing it.
 
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