Which engine oil is better???

Which oil is better for an 6.5L DIESEL egine that REQUIRES 15W-40 Oil. I am having a hard time deciding between Amsoil Synthetic Heavy-Duty Diesel Oil and Mobil Delvac 1300 Super. I can’t figure out if the Mobil Delvac is synthetic or not. I’m not even sure if synthetic is the best way to go in diesel engines. Any advice would be greatly appreciated.




Mobile does make a diesel synthetic – Delvac One. It would be 5w40 weight and would be an excellent oil. You will probably only find it at truckstops. The main reason to go with synthetic is for cold weather starting and operation. Don’t be afraid of the 5w40 designation, it fully protects at the temps a 15w40 would. Otherwise if severe cold weather is not your issue, any quality diesel oil sold today surpasses the requirements for your (older) diesel engine. Mobile Delvac, and Shell Rotella are both good choices.

One issue with a full synthetic is that if there are any oil leaks, the synthetic will find them.

Also realize that there is no consistent definition of synthetic. From my understanding, both Mobil and Amsoil’s synthetics are “real” synthetics. A real synthetic will be $4-6/qt.

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