273 rocker arm adjustment

Back in the day I had an Olds V-8 with a mechanical oil pressure gauge. Both 30 wt and 20w50 had 40 psi at cold idle. Both had 30 psi at hot idle. When I changed to 10w30 for the winter months, the hot idle pressure dropped to 20 psi, even though the outside air temp was much lower.

As far as I know, all oil loses viscosity as it heats up. And they lose viscosity at huge rate from 32 degrees to 212 degrees F. By a factor of almost 100 to 1 !!! And it is not in a straight line either. So when you drain the oil on a hot day after a long drive, the oil drains out like a cow pissing on a flat rock, regardless what weight oil you have in the engine. You can put different weight oils in your freezer overnight and do your own comparison tests in the morning.