Originally Posted by Snagglefoot
One more thing, LS engines have a spring in the oil pump that activates and bypasses oil back to the sump of the pressures get too high. I would say say it's totally strange that the pressure gage would operate at 60 psi one time and 80 psi another time, regardless of the viscosity.
I have run 5w30 and 5w40 in my 6.0 LS with the older style oil system. The pressure at highway speed, at full operating temp, does not change. Both are 40 psi, At idle, the 5w40 runs at a few psi higher.
Yup we had the 6.0 in the last boat, 40idle / 60psi.