Personally, and someone who knows more like Lakesonly or Enginedoctor will chime in as well, I would try running an oil temp guage first to see if there would be any benefit at all. I'm not sure there is.

One thing these jet boats all do well is run cool, and with large capacity pans, etc, even run pretty hard, the oil temps probably never get to the point of breaking down the oil to it's -W (warm) viscosity in many cases. In which case, what's the point? The oil never gets warm enough protect the engine as it should. Hence looser tolerances on Jet Boat engines.....

Years ago, I remember a Pennzoil tech telling me when they researched engine wear in their Racing program, 75% of all the engine wear occurred in the first ten minutes of operation, and the remaining 25% was during the hot running of the engine. Kindof explains why  high mileage cars "highway driven miles" seem to be in much better condition than a similar car with similar mileage run in town a lot.

No need to fix a "perceived" problem that, as it turns out, wasn't a problem at all, and now the "fix" became a problem....

Ray

My oil temp is usually 100* more then my water temp.

Which would put you at about 240* on the oil temp, right? Which is roughly 30* higher than a Sprint Cup engine running (Very Expensive) oil coolers to hit that temp. Well NOT outside the operating range of standard 5w30 motor oils. You'd have to get to over 300*, with your HP level factored in,  before an oil cooler, or very different oil, would be needed.

Again, not trying to burst anyones bubble here, but let the oil do what it needs to do and how it does what it does!

FWIW, Trailerho, Marc's engine is "Probably", I think is the closest quote I've been able to dig outta him, is "probably in or close to the 4 figure range".......

Ray

And I am running a 10w40 right now but am about to switch to a straight 50w....  If that helps any.. thanks!

Seams like my jet boats always had that last bit of water in the bilge the pump wouldnt pick up. I noticed the pan was always juuuuust dipping into the water, Best oil cooler you can get......

And cheaper too.. 

A gauge first is good advice.  You probably don't need the cooler at all.   I would stay away from a straight 50 weight oil, but that is just my opinion.  There are tens of thousands of jet boats out there and 98% run just fine for decades with no coolers.   Just something to think about.

Cool... Thanks for the advice.  I'll go and get a gauge tomorrow..

Let's be clear here  .  .  .   Ray is not "with" me, he just agrees with me.        He is much more likely to be found with the Vegas boys.   That crowd is a bit too swishy for me.   I am much more the 909 kinda guy w/o the black sox and flat bill hat, and boom boom stereo, and tats.   Hmmm well maybe that wasn't too good of choice of words either.  Lemme think on it somemore.

Meanwhile stay away from the 50 wt. oil.   Ya might wanna check and see if you have a good windage tray installed.   Free HP just like running lighter oil.   Just sayin'