Originally Posted by LarryBible

Everyone,

The point of "15W40" is not its WEIGHT. The point is that most 15W40 oils are ESPECIALLY FORMULATED for diesels. These oils have additives that disperse soot. These additives will keep ANY engine clean.

The WEIGHT of these oils such as; Delvac, Delo and Rotella T is the secondary issue. For your diesel it would be unwise to change to a different WEIGHT unless it is one of these oil types.

These oils have a CI-4 PLUS rating for diesels as well as an SL rating for gas engines. For your diesel, don't use an oil that does not have a CI-4 PLUS rating.

Changing to a 20W50 oil is unnecessary and will do nothing but strain the oil pump and its drive components and waste fuel. The truckers run 15W40 weight CI4 PLUS oils from Central America to Alaska and typically reach one million miles between overhauls.

You might also be interested to know that Cummins regulates the oil pressure to 15PSI. They have determined that running it higher only wastes fuel.

Have a great day,