What oil should I use in my 41 chevy??

I have a 41 chevy special deluxe with the original straight 6 with 75 thousand miles on it I just bought the car off the original owner and I'm ready to do a then up after driving it for a month or two it began to run rough so I wanna do a tune up but my simple qeustion is what oil do you recommend using I heard a lot of things like I should run diesel and all of these things but I would just like a simple answer thanks in advanced

 

If the engine is, in fact original and not overhauled in recent decades, it likely had been run a long time on non-detergent oil. That usually means a lot of sludge/carbon deposits, etc. and the use of detergent oil is usally not recommended. The problem, as you may already know, is the detergent can loosen some of this 'stuff' and that is not a good thing.

If the engine hasn't been apart in a long time, dropping the oil pan and cleaning it out is a worthwhile thing to consider. Typically, there is quite a layer of sludge and the oil pump pickup screen can easily be partially blocked.

If the engine has been overhauled in the last 20 years or so, the use of modern (detergent) oil is not as likely to be an issue.

 

Thanks for the quick reply
And I will for sure look into dropping the pan thanks again

 

For non-detergent, the store brand at NAPA appears to be as good as any. If you go elsewhere make sure it is SB rated, not SA. Any oil you get these days is bound to be better than what this engine saw when new.

 

Also your engine does not have an oil filter. So keep the oil changed out a little more often. Even if it does have a filter, it is a bypass filter and not a full flow.

Diesel rated oil is good for an older engine. Diesel oil has more ability to deal with contamination. Diesel have more blow-by than gas engines, so the oil has additives to help contain the contaminants. Your old engine likely has some blow-by issues as well.

If you pull the valve cover, look for how much sludge in there. If a lot, then stick with non-detergent oil. If fairly clean, can use detergent oil like a newer diesel rated. If you do use detergent oil, I would change it out a couple times sooner than normal as it may become more contaminated.

BTW your engine will not have much oil pressure. When cold it is 15-30, and hot will be 0-15 psi, with near zero at hot idle. It really is more of a lift pump to get the oil up rather than push it through the small passages like newer engines.