10-30 vs 15-40 oil viscosity

My '97 Nissan PU has 130K and doesn’t use oil.

Specs call for 10-30 in temperatures from 0 degrees F to 100+.

It never gets that cold in California but it gets to 121 degrees.

Can I use 15-40?

You probably can, but I suspect 10W-30 will provide more than adequate protection anyway. Is 15W-40 listed as an accpetable weight in the owner’s manual? Or do you simply have some diesel oil you want to get rid of?

I use the 15-40 fleet oil in all my high-mileage vehicles, especially in the summer. It has an added benefit. It sill contains a reasonably high level of zinc friction modifier which has been removed the latest “SM” rated “gasoline engine” motor oils in order to protect and extend the life of catalytic converters, which they consider to be more important than the life of the engine. These zinc based additives can poison a converter but they are important and necessary to protect steel against steel friction surfaces (valves, cams, lifters and gears…)

I would recommend the 15W40 only if you are doing some heavy towing, or live in Death Valley or Florida. If you live in a colder area and use 15W40 in the winter, you will experience considerable engine wear on cold starts.

Since the engine does not use oil, forget about 15W40, use 10W30 and live happily ever after. If someone has given you a case of 15W40, take it to the Goodwill and give it away!