Just found an interesting result in oil pressure in my boat engine. I always used Kendall 20W-50 but found that the pressure droped back to around 40psi @ 100 dec C. Now using Castrol 10-60 Edge Synthetic and it now sits at 60psi. Guess that shows what synthetics can do over Dino!!.

"Guess that shows what synthetics can do over Dino!!."

What does that comment mean?

nothing to do with it.

The change from 50 to 60 might

Agreed RobertC - the comparison is only valid if the vis grades are identical. The second number relates to high temperature performance. He went to a higher VI that will give a higher viscosity at the same operating temperature. Higher viscosity = more resistance to flow = higher oil pressure, all other factors being equal.