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Substitute Motor Oil Viscosity?

I own a 1995 GMC 1500 Silverado, 5.7L V8 with 160,000 miles. The owner’s manual specifies 15W40 motor oil----can’t find this grade. What’s a good substitute? Thanks,…RustyFender

Have you tried the internet? It’s gonna be a thing. You heard it here first.

Check with your local auto parts store to see if you can order it by the case, or buy it online. You could also look at truck stops.

Are you sure that your truck requires 15w40, it is almost exclusively for diesel engines. I would think 10w30 would be the recommendation for your motor.

5W30 or 0W-30 for this motor.


Agree that this oil is widely available, both as a gasoline and a “mixed fleet” (diesel & gas) service.

If you are trailer towing with your truck, I would use a 5W40 or 10W40 SYNTHETIC oil, such as Mobil 1. Heavy trailering with a 5W30 dino oil, as some recommend, will likely result in excessive engine wear.

Your model engine is the older GM type with loose clearances, so a light oil will cause oil consumption.

The last fuel injected Chevy 350 pickup I had specified 10W30 oil. If you want to run 15W40 in it, I’m sure it will work, and may be beneficial if you work this truck hard. If you can’t find this oil at a local Walmart or auto parts store, try a truck stop or similar establishment that caters to semi drivers. 15W40 is a common oil type used in diesel engines, especially newer diesel engines, so it should be fairly easy to find.

Oh man,…am I embarrassed!! After reading these posts I decided I needed to go back and re-review the owner’s manual. Yep, I mistakenly read the specs for DIESEL powered Sierra’s. Mine of course is a gasoline powered truck and the recommended oil is 5W-30. Thanks to all, I am just a knucklehead!!!

Oh man,…am I embarrassed!!

Don’t be. At least you looked.

The 15w-40 “fleet oil” is readily available and can be used in both gasoline and diesel engines —Mixed fleets…It has the benefit that it still contains the zinc extreme pressure additives that engines with flat tappet valve gear need to stay alive…The 40 weight rating is a little thick for today’s tight tolerance engines but after 160K miles, the parts fit may have loosened up to where this is a good summertime oil for many engines…It was developed many years ago to provide fleet owners a single motor oil they could use in ALL their vehicles. It was also called “universal” motor oil.