Quote:
Originally Posted by Cd
If i pull my spark plugs. there is oil leaking down the threads of the plug - pretty bad too on at least two.
I changed the gaskets, but i still have the issue.
Since i am screwing in the plugs, this seals the hole and keeps any oil from entering the combustion chamber though - correct ?
That's the only thing that I can think of that would make the exhaust smell like oil.
So if I were to run an engine with new oil, versus old oil, the emissions will be worse with the old oil ?
If so, why is this ?
What exactly causes an engine to produce more poison emissions ?
"Motor oil has additives to counteract acids from blowby. Those additives get used up.
If you had an engine with really good filtering, analyzed the oil regularly, and added additives as needed, you could run the same oil forever. It's cheaper to just change the oil, though. "
So if I understand correctly, an engine will produce more emissions once additives in the oil are used up ?
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If you have oil accumulating on the spark plug threads, it is either coming past the rings or valve seals, or it is leaking out of the valve cover gasket and pooling in the recesses where the spark plugs are located.
The second scenario is in engines where the plug is located in a recess surrounded by the valve cover with a cup and gaskets to seal off the plug and cup.
The threads on the plug, being located below the crush washer can only accumulate oil from the combustion chamber. When we changed plugs that were through the valve cover, as well as most any others, we blew the recess out with air to get any accumulation of oil and dirt out before removing the spark plug to prevent the accumulated debris from falling into the combustion chamber with potentially disastrous consequences.
The type of engine and the oil consumption would help with any diagnosis, but regardless of the type there is oil consumption and that is what you are smelling. It's also the most likely scenario that produces the smell you describe. Most likely the catalyst's function has deteriorated due to oil contamination which also produces the"sweet" smell you describe.
Why it would be more prevalent with fresh oil?
Not sure on that one, but I can smell them on the highway. One exception is leaking valve cover gaskets which can fill the spark plug recesses with oil as well as leaking onto the exhaust manifold. Sometimes I can see the smoke from the burning oil when the car is sitting at a light idling.
regards
mech