can i use diesel oil?

I swear by Rotella diesel engine oil. I know some local racers who run it. Awesome stuff, and not terribly expensive either.

SE-designated oil is a very, very low grade of engine oil, Basically, it's the minimum grade of oil for use in engines manufactured up until 1972. To the best of my knowledge, they don't even make it anymore. The grades go by letter: SA being the lowest grade that exists, and SJ being the minimum standard for use in cars today. It's worth noting that even the cheapest oil you can buy today is better than SJ. (which is WAAAAAAAY better than SE)

If the oil you've got is SE, I say cut your diesel fuel with it. Lots of people I talk to cut diesel fuel with between 10-25% Old motor oil.

SAE isn't the grade of oil, SAE stands for School of Automotive Engineers, and they make the standards for how engine oil viscosities are designated. For instance, SAE 40 oil, is 40-weight oil, as defined by the School of Automotive Engineers.

In the case of SAE 15W-40, It's a dual viscosity oil, that due to stuff added to the oil acts like 15-weight oil when it's cold, and acts like 40-weight oil when it's hot. Same as 5W-30, acts like 5-weight oil when cold, and 30 when hot.