Thanks to everyone so far for the input

572" carbureted engines, standard mercruiser sea pump, transom mountned pick-up, sea strainer, stainless crossover inlet, 1-1/4" hose plumbing. Pretty basic in my opinion

The 900sc and 1000sc engines, used the flywheel housing coolers. They used the 8 plate cooler, one on each side, as oil coolers, plumbed together. So they had two 8 plates for oil cooling. For the transmission, they used a tube style cooler. I believe the 750 supercat racing engines were set up that way as well.

From what it seems, mercury marine, was never fond of hot oil. Most black engines never got over 200*, and i believe on the newer EFI engines, the oil temp alarm comes on at 220 or 230* , on the 525, 700sci, etc , if i recall. I am not 100% sure on that.

Even though we get excited about the moisture thing, we must remember that even though the gauge is reading xxx temp, its an average. I am sure if the gauge is showing 200, the oil at some point, is seeing higher temps. Whether its coming off the cylinder walls, the pistons, the bearings, the valve springs, etc.

I dont really care that an oil is "rated" to lubricate well to 300 degrees. Oil doesnt just lubricate, it also cools parts. And in a marine engine that sees extended high loads, parts are getting hot.

Just my opinion. Im not an engineer.

I will say I had a lot of condensation issues from the start and tried solving it for years , I was able to get it to be better but ultimately with the new motors Ive had no issues whatsoever. Not sure if the problem was.. maybe all the blowby from the Choo choo motors ?? but it`s all gone now so it may not have been an oil temp issue but making the oil hotter was probably just a bandaid but it did help somewhat.

I struggled with this goo issue for way too long, should have just rebuilt em the first year. Live and learn

Gentlemen, this is all good info. I'm in the process of rebuilding my engines and trying to address the appropriate items while the engines are out. I'm also looking into oil t-stats and that's a whole separate issue that needs researching. For the way I plan to run the boat I think the 8 plate is worth a try as I think an upgrade to a larger cooler is pretty easy if necessary. Most of the used set ups are 8 plate so it's an easy thing to try. My target oil temp was the low 200's, enough to address moisture issues and well within the limits of most quality oils. As Mild pointed out the oil helps cool things like the bottom of the pistons.

This turned out to be a good (productive) conversation, any additional input is appreciated. Now I just have to find 2 good flywheel housings with coolers.

If you're interested I have 2 mercruiser bellhousing oil cooler combo transmission style that I would be willing to sell. They're in great condition. Pm me a number and I'll shoot you some pics. I have the plate coolers adapters and bell housings.

4500 to 6000 for 100+miles at a time,what size gas tanks do you have?

Based off of his lbs/hour fuel usage on the dyno and the speed his boat runs, he is still around 1 mile to the gallon. His boat is very efficient, so around a hundred gallons.

PM sent

1 mpg at 6000 rpm seems high to me,i was hoping he would answer.

HA! Joke of the week.
1mpg is a dream. How can you compare a dyno pull and pushing a boat thru the water?

1.1mpg with a pair of 500EFI and bravos.(boat test)

75hp robbing #4`s and 560 extra hp= 1mpg?? Those are some magic motors.