Inliners International Forums General Discussion Engines 235 recommended oil weight?????

after my last post you guys mentioned i should be running sae 30 weight on my 56 235 so i swapped out the 20-50w for Rotella T sae 30 and i noticed a drop in oil pressure. with idle set at 800rpms i got 10-15lbs of psi, reving to 3k gives me about 25-30 and it really wont go above that. with 20-50w i had a solid 35lbs at anything above 2k and upwards of 50 or so above 3k. what gives?

i would recomend rotella 15-40. the loss of viscosity is causing the lower pressure. tom

There seems to be a lot of controversy concerning the viscosity of the oil for any engine, especially for the classic Chevy engines. What are the clearances on all of the main, rod, and cam bearings? I have always felt (based on 50+years of building 216-235-261 engines, but with little scientific experimentation) that a SAE 30 oil has too high of a viscosity for a cold engine, but maybe not high enough for a hot engine. I am using Shell Rotella 15W-40 in my 278 cubic inch 261.

Watch where the "W" is in the oil viscosity description. It is almost always attached to the first number. The SAE 20-50W is probably 20W-50, indicating that the oil meets the SAE 20W viscosity specification at cold temperatures and the SAE 50 viscosity specification when hot.

I suspect that your pressure with the 20W-50 is higher than desirable, but that the pressure with the "straight" 30 is too low, at least when the engine is hot. Try 15W-40 or 20W-40.

It seems that tlowe and hoytww posted our replies at exactly the same time with the same recommendation! is that coincidence or...?

yeah I ran 20W-50 VR1 valvoline racing oil in my truck for four straight summers, in my 235 in my truck and it never ran low on the preasure gauge unless it was really hot outside in summer, like 118 degrees here, and for those couple months I would use SAE straight 60 weight and it ran great, never spun a bearing, never thru a rod, in the winter 30 weight is probably good, but in the summer I would step up to either 15W-40, or 20W-50 so that the motor oil has the capability to adjust to the surrounding outside temperature demands and keep your motor safe, but depending on where you live and surrounding temp comditions determines a lot, I am not saying my statements are scientific law or anything, just saying it worked for me.

Gentlemen;

Multi grade oil doesn't work well in the 'early' engines. It never has unless your in a 'freezing' climate etc.

It's to thin to lubricate properly, which is why your losing oil pressure.

Happy trails.