I know this is a very dumb question but what does the 10 and 30 mean in "10w-30" and what is the best weight of oil for a lt1 with 127000 miles on it. Also I just did the intake leak repair and the engine had a dark tan in the metal with a little bit of sludge on some of the metal as well. I have used seafoam in the oil but really want to clean the engine very well. I bought some Moble 1"Drive Clean Plus" tonight for high mialege veh. I have been using moble 1 5-30 synthetic. What is better and how do I clean that engine better??

 

I run mobil 1 10w30. You and I have about the same miles, 10w40 would probably be ok too.

The numbers have to do with viscosity, the first number is viscosity when cold, the second number is viscosity when hot. Higher number=thicker.

John