15w30 or 15w40 are common for "all around" usage. Make sure it's oil specifically for diesel engines.... API CJ4 is mandatory if you have a more recent model with Selective Caralytic Reduction, and is compatible with earlier Diesel engines.
You can only use the fuel oil in the diesel truck.
The Oil you want to use is 15W-40, if your truck is higher mileage I use Amsoil's Heavy truck/ Marine 15W40
15W-30 or 15W-40 diesel oil is generally used as an all-around engine oil. Specific oil for diesel engines must be used. Any 2009 or newer engine (in the US) must use API-CJ4 low ash diesel oil.
Just use a good quality oil that is designed for diesel engines.
I believe the engine is a Detroit Diesel 170. The truck has about 900K in miles on it. I've always used Mobil Delvac, but someone told me that I was wasting my money. Any suggestions?
If you cannot see a leak on the ground under the truck (and you should with this much oil) it sounds like the piston rings are pretty well worn out.
Any internal combustion engine will use oil.
Gas: 5W30 synthetic, gasoline-rated oil. Diesel: 5W40 synthetic, diesel-rated oil.
That one should be diesel, so any API-CJ4 15W diesel engine oil should suffice.
If you are talking about standard #2 diesel fuel oil and not motor oil and you have a #2 oil fired furnace or boiler in the home the answer is yes .