Had the boat out yesterday for first run of season. With the 20w50 merc oil it ran 38-40 PSI at WFO. Would Idle cold at 20PSI and after coming down from a lng run it would idle at 12PSI and then climb back up towards 20. I did notice that running wide open for about 3-5 minutes the oil pressure would drop from 38 down to around 35. only ran boat for about 2 hours and no oil consumption. It would use it when it had the Amsoil in it. Just waiting for mech oil guage to double check but I am sure it is just my guage.

How many hours on that 502 ?

240

Seems like low hours for a rebuild. Definitely check your actual pressure, etc....

Now with 25 hours back with the Merc Oil 25w50 it isn't using oil and PSI is now staying just over 40 with the new therostat running 140-150 temp instead of 170.