Originally Posted by AF
Oils like the High Mileage Castrol and Mobil 1 (to a lesser extent) prevent burnoff because they swell the rings.
They also do a good job at cleaning out carbon deposits through their extra detergents which is a mixed blessing. Higher mileage engines tend to have a nice layer of carbon on the piston top which actually bumps compression. With that gone though, you have a much better surface for the fuel to atomize.
I have a nice, thick, black layer of carbon on everything
Why would Mobil1 swell the rings? I don't quite understand.
How could one clean the carbon off the pistons? Would seafoam or similiar do it? I always assumed the detergents in gasoline would cook carbon off the pistons.