Unless it's a fresh rebuild, it's hard to beat plain old HD 30 weight oil in a 235, especially in the summertime. It gets a little thick on a cold winter startup. I've used 20W50 year-round in a lot of engines. The 10W30 and other multi-weight oils don't actually thicken up as they get hot, they just lubricate like the heavier weight rating. So, a 10W30 stays the thickness of a 10 weight all the time, and if there's a lot of clearance, oil pressure will drop as things heat up.
A fresh rebuild with very close tolerances can use the lightweight stuff without a problem. A high-volume oil pump will flow more oil hot or cold, and the pressure will go pretty high on a cold start. Once things warm up, the pressure will still drop, but not enough to let the lifters bleed down.
Jerry
