Just recently had a gen. IV 454 built by very reputable engine builder for 28 Wellcraft Scarab. We broke the motor in on dyno with 500hp & 550 ft/lbs. Got the motor back, installed all accessories, and ran it on stand for a little bit to make sure all was working good before going back in boat. Got motor back in boat and started putting some water time on it. This is where my problem starts. Upon starting it up it is building about 40-45 psi oil pressure. As I run the boat and oil temp comes up I start loosening oil pres. Oil never gets hot to the point you can't lay your hand on the oil filter. It got to the point (last time out) oil pressure dropped all the way down and motor got noisy. Pulled motor, back to engine shop and was torn back down. Destroyed the crank and all main and rod bearings. Engine builder can't figure what went wrong. In doing some research the oil cooler configuration has me really concerned. Just got motor back and DO NOT want to do this again. I am running factory oil/ps cooler with factory block adapter and oil filter relocator. The oil pump is a high volume pump and I have heard the factory oil cooler system will not work with a high volume pump. Any help or thoughts would be greatly appreciated.

I did the same thing to my motor on June. I have a 1986 Scarab with twin 454s. We still haven't figured out what went wrong. I haven't put motor back in boat yet either....

You will need a much larger oil cooler than stock. Ditch the combo PS/Engine oil cooler. You also have to upgrade the oil lines and fittings so flow is increased. There is a ton of info here on this subject. Good luck.

You can try tap temporary temp sender and monitor oil temp readings here and there I've seen em with 6 qt systems remote filter puny cooler too hot to touch .maybe you have some bypass valve issues ,and some junk went around. Filter through lower end ? I like to prime system with coolers ect in place before install to watch oil flow ,and make sure oil pump drive system isn't too overtaxed .(good air drill and chuck trying to rip out of your hand while priming )

Are you sure you did not reverse the oil lines?? If you did no oil will be filtered or cooled.

** just reread your post. - Destroyed the crank and all main and rod bearings -

You have to install a NEW oil cooler, there is no way to clean or flush the old one. I even replace the hoses with brand new. It's not worth the cost.

What was the reason for the original rebuild? Did the engine grenade? If it did the oil cooler should be replaced and oil lines at a bare minimum flushed but if it were me I would even replace them. Not saying that would cause 0 oil pressure but if it sent contaminates through the oil system and wiped the bearings that would certainly contribute to your issue.

the factory oil lines, filter adapter, block adapter, cooler all are junk, need H/P stuff with 1/2" fittings, # 10 lines, napa gold or wix filter...tons of info on here about this...at this point I would have serous thoughts about your engine builder...what I mentioned is needed, but did not cause what you have unless metal was everywhere and you did not get it flushed out...and thats almost impossible

^^^^^^^^ what he said^^^^^^^^^^

If your looking for a new cooler try Mr. cool good prices

after the builder did his thing the engine was run on a dyno so i dont think the builder did anything wrong or the problem would have shown up on the dyno.i suspect that the oil lines were put on incorrectly and that toasted the bearings.when i finish running one on the dyno and reinstall all the accessories i reprime everything with a manual gauge installed to confirm that the oil lines are in the correct position.it is an easy mistake to make.