Been trying to figure this problem out. It's a 510 B&M 420 Mega, crossover/bypass. After 30 hrs the starboard engine oil is milking up. Port is fine. We pulled the intake, changed the gasket. Headed to the pond. Ran the boat easy 3000-3500 rpms all day monitoring the oil. It was fine. At the end of the day pulled some 5000rpm runs and sure enough MILKSHAKE Is a head gasket next in line? The water psi gauge is not working on this side but the other engine reads 22psi WOT. Kind of running out of nice weather but I really want this fixed before winter storage.
Thanks

Swap W/P guages and try again. Could also be head gasket

Yep, probably a good idea. Both bypasses look to be kicking out the same amount of water but at 5000 rpm who can tell without a gauge.

Too much water pressure. Could still be the intake or head gasket. My bets are on intake. (disclamer, I have been wrong a few times now)

We had a motor in a friends boat & it drove us crazy. After the 3 or 4th set of intake gaskets we took torque wrence & tighen down bolts.Warmed up motor, had to retighten. ran again & had to retight. This went on for 4 heat & cool down cycles. After the last time when we recheck torque everthing stayed the same & water in oil problem when away.

Thanks Turbo--We Torqued after one heat-up/cool down cycle. Was your problem all the time or just when you ran the boat hard?

There is not a crazy amount of water in the oil. Just barely enough to make it a little milky. The oil level does not raise a bit.

What Water Temp Is The Engine Running At?

Around 150 degrees, Oil Temp will hover around 200-210

Josh -

Just a suggestion.....
Make sure you aren't getting more water than you think. After things cool down, crack your oil drain plug just enough to let a little oil from the bottom of your pan leak on your hand. I had a really bad time after my supercharger was installed finding a water leak. It didn't look bad on the dipstick but after the water settled out in the bottom of the pan, the oil plug test showed me vanilla (not chocolate) milkshake. I was getting a lot of water.
I hope this isn't your problem but my case turned out to be a .020" flatness issue in the deck of my block between a water passage and the oil galley. Things were fine with stock power but the added stress from the blower, eventhough my heads were shaved and I used aftermarket head gaskets and ARP head bolts, was enough to uncover the flatness issue.
I still blame the engine builder here in Phoenix for not being thorough and checking the deck of the block before installing my heads.

Oil And Water Temps Are Real Good!definatley Not To Cold To Cause Condensation