Dock, did you check the oil before you bought the boat?

How can the hose cause reverson.That's more with big cam overlap and long idle and would show up more when you pull the heads and will find the valve seats have a dusting of rust .I run on any hose shop or at home full on and never show more than 10lb. at the oil cooler.

If you check raw water pressure at idle in the water it is between 2 and 5 PSI. 10 is too much at idle. The exhuast isn't making enough pressure at idle to hold it back and you wind up with water in the clyinders and then the crankcase.

Dockroacker, I would also recomend pulling the pluga and cranking the motor for a while to puch all the water out of the cylinders if any has gotten there and then spray some oil in each cylinder. WD-40 is fine. You will want to do this stuff fairly soon before the water has a chance to pit the clyinder walls and valves.

ditto

lotsa pics here to help you tear it down.

http://www.mercruiserparts.com/selec..._nbr=809994965

Positive displacement pump , nothing you can do to adjust pressure..more pressure on the inlet side should not effect the outlet side.

Theoretically positive displacment in a perfect world. If you turn the hose on but don't start the engine water comes out the exhuast after a while. We installed a reman 502 from Merc in a boat last year. After 20 minuits or so of ideling we found milkshake in the oil. Called Merc and they said don't run on the hose under 1200RPM for more then a few seconds. I argued with the guy on the tech line for 2 hours saying the same thing you are. He insisted that I flush the crankcase and see what happens. No problems after that. Can idle all you want in the water but not on the hose. Boat as had no problems since.

Im not doubting your results ..I just cant see it without some other problem..Water always leaves after the elbow ..unless you have waves rushing up the pipes..
Although water is coming out the hose at 40-70 psi. So I guess

It's a rare occurnace and according to merc it is most common when the exhuast hoses are level or have very little downward slope wich makes sense. Just not enough exhuast pressure at idle to clear the excess water that is moving past the seawater pump due to excessive hose pressure. That was their splaining anyway

If it was from too much inlet pressure at idle causing reversion AND he has test ran both motors wouldn't they both be contaminated? I believe its possible but i expect something worse,Smitty