after a good amount of research, the type of oil really doesn't matter in a old flat tappet engine, as long as 2 things are kept in check: proper viscosity for the driving conditions, and a proper amount of ZDDP, which provides the cushioning effect for the cam and any other loose clearance parts in the engine. its also important that your seals are good if its a particularly old engine with a lot of miles or age, as synthetic can cause more consumption of oil or leaks.
after knowing all of this i will be making the switch to valvolines racing high ZDDP oil. diesel oil is perfectly fine but it seems to hold more of the deposits created by the engine, despite having a good filter. its not too much more and for someone who wants a lot of life out of my 235, that's what i will go with.
i change my oil every 2000 miles anyway, which is every couple months, as my truck is a daily driver, and i dont feel like adding ZDDP to my oil every time i do a change.
i also use a quart of lucas oil stabilizer, which would add the necessary viscosity to any synthetic i might ever add to it. it also helps my oil pressure and overall cling of the oil.
Last edited by Mr. Dane; 12/06/2020 7:22 AM.
