Originally Posted By: Fastship
Originally Posted By: Jim Allen
Originally Posted By: bruce381
Do these two things automatically go together? - low viscosity oil and low oil pressure?
all things equal viscosity will effect pressure
That has been my experience. Coupla years ago, I switched two of my diesels from 15W40 to 10W30, noting the oil pressure with a test gauge before and after the change and the pressure dropped a little with the 10W30... just a few pounds (with the oil temps approximately the same with each) both. "Low(er)" oil pressure but not "low."
As has been stated earlier, it then comes down to flow. I'd be surprised if the flow didn't increase by roughly the same percentage that the pressure dropped. What I know for sure is that, the following winter, the tractor spun over lots better.
hmm - but how confident can you be that there is sufficient flow lubricating your engine if the only reading you have is pressure?
My yardsticks on that were the factory "normal" oil pressure specs for the two engines in question. Few of us have the tools to actually measure flow but the way I see it, if you have a reserve of pressure above the norm after the viscosity change, you are golden. As I said, the pressure went down just a few psi (3-4 IIRC) but was still way above the spec listed in the factory manual.