I am stumped...
I bought a 1997 502MPI with 480hours from a fellow that did not want to deal with rebuilding.
The problem as described to me:
The oil pressure seemed to steadily drop throughout the season; starting out at about 45psi and then toward the end, like 35psi.
At the end of the season it would drop off the table to below 10psi after a hard run of 4000+rpm. The pressure would hold at 35psi until the throttle was pulled back though. If he would run her real easily, not over 3200, the pressure would be like 25psi when throttled back.
The boat is equipped with an oil temp gage that never read high...

I have now completely torn this baby to the bare block. I can't find a anything wrong.
The bearings look to have vary little wear. Not even one bearing surface has a scratch.
I have not miked the crank yet, but I can't see a need to. This engine looks like it could have gone another 500 hours, no problem.

Could it have just been the oil pump?
Is there some way I can test it?
Ideas please...

I had the same problem,,, changed out the sending unit,,,, 60 lbs.........

I had a similiar problem last season on my 540. Engine cold, 65lbs at 900 rpm. After a 5 minute run at 3500rpm, oil pressure dropped to 10lbs at 900rpm. I swapped sending units, gauges, and it ultimatly got pulled and torn down. It was an eagle crank, which now i find that lots of people have problems with them because out of the box they were not always true. First engine builder slapped the motor together with some parts but did no machine work it appeared. Motor also had some carb problems, which I believe to be the cause of fuel washdown and tuliped valves. Motor was a mess, main caps, bearings, valves, crank reground, wrist pins, rings, etc, it was all replaced, balanced and bluprinted. After a 7000 dollar rebuild, it has ran flawless the past 10 hours. Oil pressure drops to about 50lbs after a hard long run, and then after a few minutes of idling it cools off and stays around 60.

Sorry for the long post, hopefully its a sending unit. After doing hours and hours of research on this topic, it seems that 75% of the time its time for a rebuild. If you are gonna rebuild it, now is a GREAT time! Better do it now while its out rather than put it back in and somethings wrong and it goes BOOOM!

I had two new engines two years ago , one with twenty pounds LESs oil pressure than the other ....also a bad sender . Cheap fix.

Hi guys,
I guess it could have been the sending unit. Wouldn't that be the s--t...
However, the engine has two sending units. One for the gage and one for the alarm circuit. The alarm was ringing when the gage read low...

I'm having the same problem with my small block engine. Tried everything..checking gauge, sending unit and wires. Even went thru the cooling system thinking there may be a water flow issue that wasn't showing up on the water temp gauge. Nothing. Engine is coming out this weekend. Let me know what you finally come up with as the problem. I'm thinking either oil pump or cam bearings spun preventing oil flow. Engine has 260 hours.

Well, I have the engine down to the bare block at this point.
The block is go to the shop for a good cleaning, new cam bearings, and honing.
Then I'll blot her back together with new rings, bearings, and oil pump.
And yes, new sending units...

Put the oil temp sender in the pan or at the oil coming out of the eng before the cooler some times the sender is in the wrong place.Use 40w oil or I like 15w50 Mobil 1 in hot running engines but that is another subject.

Oh yea, I'm buying a new oil cooler too...

I know that this isn't your problem, because your oil temps are in line. I've always run 20w50 oil. After everybody telling me not to run multi-vis, I switched to a straight 40w. Sure enough, after about 30 minutes of running, my oil temps went up and the pressure dropped. At the worst, I was seeing around 30psi at 3,000 rpms. The straight 40w oil was breaking down under the sustained heat. I'm going back to 20w50