I wonder if your cooler is partially plugged causing the bypass in the filter to bypass most of the oil past the cooler?

3 X 18 oil cooler should be good for a min of 750 HP @ 6000+ RPM. If your cooler is good, you haven't likely found your problem.

Do a search on here for oil pressure by pass valves. It's located in the oil filter pad on the block.

If it's the stock valve, the oil will take the path of least resistance and by pass the filter and cooler.

its a dart block. I dont believe it has the bypass valve.

What is the jetting in the carbs and what carbs? Lean will cause this problem.

Do you run flat tappet lifters and is so what is the seat pressure?

But in all likelyhood the engine clearances were set up too tight. Do you know the rod and main clearance? What weight oil are you running?

the cam is a hydraulic roller, the carb is a pro systems dominator I will have to look at the jets again. the plugs are nice and brown. I ran the boat shut it off and checked them. I dont have the rod and main clearances but I will find out what they are. I am running valvoline vr1 race oil 20w50.

Make sure your raw water pump is good. I recently had higher than normal oil temps with normal coolant temps and what appeared to be plenty/normal amount of water out the back. Changed the raw water pump and all is well.

its new but I will pull it off and check it anyway.

I had the same issue last week and also had a loose belt so at idle all and low speed cruise all was fine but above 3500 rpms oil temp would start to creep past 220 deg. After cruising @ 3800 for about 45 minutes it slowly made it up to 260-270 deg before I decided to back down to 3400 and let it cool. I was nervous it was blow-by or a bearing going away so first I decided to replace the raw water pump, back-flush the cooler and tighened the belt and all is good for me.

Check your carb jetting. 2 jet sizes are enough for mine to run 20 degrees hotter oil.