A. Actually, Cummins recommended a multi-grade oil 15W-40 in this engine which offered several benefits versus a straight SAE 40 Oil.
However, since you have apparently been using a straight grade SAE 40 for some time with no problems and this is an older engine, CITGO offers a product called CITGARD 600 SAE 40 Heavy Duty Engine Oil.
If you are operating this unit in an area where there are seasonal temperature changes, an SAE 40 does not flow to the engine gallery from the oil pump during cold soaked engine starts below 32F without auxiliary block heating.
by Mark Betner, Lubricants Expert
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Posted @ Wednesday, November 20, 2013 12:00 AM