well... this is all educated guesswork , of course... but ...

the cold pressures sound close but 40-45 is low cold... and what you describe after some time at hi revs sounds a lot like an oil temp deal.. either the temp is very high or the clearences are such that even when the oil is at 210 it is now too thin for the clearences... and i suspect this because of the low cold pressures. now all this is predicated on your gage being correct and all the normal stuff. engines don't make sludge by sitting. so i think you are wrong about that. i don't think its a supply issue at all. if i was standing where you are i would do the following: change the oil and the filter to a straight 30 oil... any name brand. i would cut open the old filter and see whats in in it. i would sniff the old oil to see if it smells burned or full of fuel. i would have the oil cooler off and make sure the water passages are clear. and i would put a mechanical gage on it that i could just drape the line up to where i could see it when i was driving the boat and try it all again. if , in fact, it really does start dropping pressure as you say when it gets hot and that would mean that when it idled hot it would be at about 5 or 10 lbs, then you have some sort of bottom end problem. bad mains probably... but if the pressure fall off hot at speed but still idle at 25 or 30, hot then thats going to be something else... something unusual...

i wonder if the relief valve got rusty and isn't sealing up well... or something simple like that... but at anyrate... spend some time and do some simple straightforward diagnostics and then go where the data sends you...

I just pulled one of my motors down because of a loss of oil pressure. Mine would start up and be a solid 40 pounds, after about 10 - 20 minutes of solid running, pull back to an idle it would drop to 10 - 15 then if it idled down to 500 rpm it would drop on down. Pulled motor apart and found #2 main bearing spun. No noises no loss of power. Hope this will help you.

Sounds very close to what mine did when the oil got hot. Only difference is the pressures, yours look low to me. I'd follow Stevesxm's plan, but if you can get an infrared temp indicator, I'd check the temp of the oil filter when running WFO as a proxy for oil temp. the filter casing surface will be 10-20* low, but it will give you an idea where your oil temp sits. Obviously, you'll need a friend to do this. Or get an oil temp guage.

Interesting thread since I just had a newly built 454 lock up on me...it would run good oil pressure until a hard run and when throttled down it would drop very low. Am curious about the comment on a spun bearing...someone has suggested that I could have had a spun bearing and then the crank broke. Techs taking it apart next week or so to see what went wrong. If this is it, how exactly do you keep it from happening?

well.. it sounds like a wise ass answer but the truth is that if the motor is assembled competantly from parts that are correctly measured and correct for the task then thats all you need to do.
100 out of 100 times when fresh motors fail it's because someone screwed up along the way. now... it's easy to say " gee the machine shop screwed up the crank sizes so it blew up" but ultimately and absolutely and without exception it is the responsibilty of the guy putting the parts together to make sure everything is the correct size and configuration before its installed. the buck stops there. if you can't measure bearing clearences and are relying on someone else to tell you its ok for you to put together then you are not qualified to be doing the work. and when it blows up you have absolutely no one to blame but yourself. nothing happens by accident. if you put all the right parts in all the right places in the right manner then you don't have these issues.

there are no exceptions... certainly you take calculated risks along the way. if you have a perfectly good running motor and it needs freshening, then you don't send the block out for e xray or magnaflux... you assume its not going to be cracked when you are done because you know it wasn't cracked when you started... and if you are wrong and in 10 hours it does crack you shrug your shoulders and say " oh well" ... its still your fault but you made a rational decision based on sound information. but if you get a motor out of a junk yard thats been sitting in the snow for two years and don't crack check it then you are dumb... and everything elses is something between those two extremes.

There's a whole lotta truth right there... Every word of it. :drink:

:flag:I had some low oil pressure issues just recently.The engines were fine in the the last season.This year started to show both engines dropping in pressure.Long story short.Check your electric connections.I cleaned mine and now I have normal oil pressure.Resistence on the wires wire will lower the oil pressure indication on electric gauges.

thats correct. thats why every oil pressure related thread always has " put a mechanical gage on it and confirm the numbers" in it somewhere. just like this one...

" i would have the oil cooler off and make sure the water passages are clear. and i would put a mechanical gage on it that i could just drape the line up to where i could see it when i was driving the boat and try it all again. if , in fact, it really does start dropping pressure as you say when it gets hot and that would "

The best oil pump is the OE pump at the local Chevy dealer. I suggest buying the Mark IV pump that has the pick-up tube welded in place already. Not sure of the part number but I believe it is GM # 3969870. They are not much more expensive than the Mellings but of higher quality. There is a difference between the OE Pumps.
The Mark IV pump will not fit on a Gen IV or Gen V main cap because of taller main cap bolt bosses. Take yours to the dealer and compare.
Dennis

Also, you mentioned the guys at the local boat shop talk about the "Heavy Duty" oil pump.

GM calls the #3969870 oil pump the "Heavy Duty" oil pump.

Dennis