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To reduce emissions, the land between the top of the piston and the top piston ring has bee reduced in the latest generation of vehicles. This makes the top ring much more likely to coke up. This is the hot spot. With water cooled turbo bearings, concern for oil coking in the turbo bearings has become secondary.
New oil specs were developed to address the piston ring coking and the newer oils meet that spec. However, dyno oils will break down and coke and true synthetics will not. Group III oils like Castrol Syntec are highly hydrocracked mineral oil base stocks. Get Mobil One. Don't pay the same money for Syntec!
For a higher milage vehicle, you might consider a 10W40 or 5W40 true synthetic. I do oil changes for a 97 DTI Passat diesel, and I tried the 5W40 Mobil Delvac full syntheic diesel engine oil in my 95SET. I like it. The engine seems smoother and quieter. My fuel consumption does not seem adversly affected. Got 31 mpg on my morning commute with flat winds and 32F temperature. (Mobil states that the Delvac is excellent for gas engines, but they do not actively market as such.)
With a older engine like yours, I suggest a can of oil addative that claims to free sticking rings one week prior to the switch and use a can of oil flush as well. Read and follow the directions! A true syntheic will release the sludge and varnish in your engine, so don't extend the first drain interval. Use a better filter. Get a Purolator Pure One filter. It is a really good unit and does not cost the $10 to $11 US that Mobil One wants for theirs.
I have rebuilt a V8, done 2 or 3 4 cylinder auto rebuilds and two marine engine rebuilds. The biggest problem was always stuck piston rings. These often could only be remove in pieces with a hammer and driver. Stuck rings can also break and score cylinder walls. Sometimes a can of stuff to free sticking rings will free sticking rings and restore a smoker to normal oil consumption.
If you have any leaks in your engine seals with dyno oil on an older engine, these could get worse if oil deposits are now part of the seal interface.
posted by 207.43.19...
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