I just got back my car from the mechanic because it was breaking up under power regardless of the engine being hot or cold. After checking the spark plugs, he got to the #8 plug and told me it had burned oil on it. He showed it to me and definately looked screwed up. He told me that was a bad sign because either it was a leaking seal, or worse a bad piston ring. We had already been talking about replacing the valve seals because it would fart a cloud of smoke from oil at startup. He said to give it some time to see if it fouled another plug.

My question is whether or not there is a way to choose whether it is the valve seal or piston rings. If I fix the valve seals and it is the rings, then I'm out the money or vice versa with changing the rings first. I'm hoping it is the valve seals or else I had better start saving up some money.

 

Usually bad rings cause excessive oil consumption and oil sludging. The valve seals will cause that blue smoke on startup you describe. It's kind of like a leaky fuel injector, if there's a bad seal on an intake valve it will leak out slowly when the vehicle is off, and when you start the vehicle the oil that has built up on the intake valve will get sucked into the combustion chamber. That's just my opinion, anyway. Your piston rings may be bad as well but they'd have to be really bad to get oil in the top of the combustion chamber. What's the mileage on the vehicle and what kind of maintenance record does it have?

 

The engine itself has about 18k on it. Was a rebuilt with some performance mods on it, nothing major like a stroker kit. I haven't been seeing it burn oil while driving, which I think is a big indicator of bad rings....just at startup.

I've kept maintenance at the best level I can, from engine breakin to running synthetic oil the entire time.

 

Get the car to normal temp,run for a couple of minutes at between 2500-3000RPM's then goose it hard from the 3000 and let it come back to idle for just a second and goose it again. If ya got smoke ya got bad seals. Done in the driveway.

 

The most common cause for fouled number 8 plug on a stock motor would be a leaking intake gasket allowing it to suck oil from the lifter valley into the intake port. That said rebuild quality is spotty compared to OEM engines so you could have bad seals or rings. I don't know your situation but people are far too quick to rebuild these things and all too often have problems with the rebuild they likely never would have if they left the stock shortblock alone.

 

You could perform a compression test. If your rings are bad on 8, you shouldn't get near as much compression in the 8 cylinder. But your symptoms seem like valve guide seals.

Z

 

I have yet to see bad rings on a car causing it to burn oil since 1975. Oil at start up and no other time is usually valve seals. One thing I do see a lot of is cars that are not driven enough. The drain hole in the back of the heads gets clogged with sludge and the oil puddles back there so much that it overwhelms the rear valve seals. If you take off your valve cover, don't be surprised to see a bunch of oil come running out.

BTW the only causes of burning oil I've seen from experience are seals, head gasket or intake gasket. Rings could do it but I've yet to see it. I have seen bad top rings due to piston damage from Nitrous but that's it.

Don't waste your time with a compression test. Always do a leak down test.

 

The car is also my daily driver, with no nitrous or forced induction putting stress on it.