Schaeffer Manufacturing Co. 0700CK4-012 SynShield Durability Advantage 15W-40 Diesel Engine Oil, 12-Quart Bottle (Pack of 12)

This oil company is the best in the biz!

Swapped to schaeffers from Rotella 15w40 and noticed increased oil pressure, slightly better fuel economy, and a quite engine. I was quite impressed. Its really good oil, but... the downside is the price, I recommend going through a nearby sales rep as the prices are exponentially cheaper than buying from a 3rd party vendor such as Amazon, Napa, O Reillys etc.