Thanks for that advice on fuel in the oil. We just ran the engine pretty hard on a ten day cruise around the Delmarva Peninsula with out much wind. I am about to change out the oil with Rotella 15w-40w. We had been using Castrol 15w-40w. The engine is starting to get into the 190 degree range when I run the rpm's above 2200 leading me to think heat exchanger needs to be serviced. I'll change out the impeller as well. I was thinking the high temps may have something to do with a drop in oil pressure.
If you do have diesel thinning the oil the diaphragm of the fuel pump is probably ruptured, if this is so you should see a rise in the oil level as well.
On the rise in temperature, if you have a heat exchanger on a 22HP 3GM you have a 3GMF. I found I had the same problem with my 3GMF and it turned out to be the small elbow on the water injection into the exhaust elbow. These engines also suffer from the exhaust elbow itself becoming blocked with carbon and corrosion. The heat exchanger is of course another point to check as you already noted.
I think you may have nailed it. I do have a 3GMF. The last time I looked over the heat exchanger I ran some welding rods thru it. It looked pretty clean. That was about 175 hours back. I'll check out that exhaust elbow. I may have overfilled the oil level bit when I was topping up after 26 hours of motoring. Do you think this could have affected the fuel pump diaphragm? I found it curious that when I went to top up after another 10 hours engine time that the oil level was just above full.