Overheating with jet but not with prop

[bullspoonie]

Hi. I have a 1992 200 hp Yamaha 2-stroke outboard with factory-installed jet drive. I have since bought a prop lower unit and I switch them back and forth with the season. The engine has started overheating when the jet is on but not when the prop is on. It overheats after idling for about 5 minutes. There is a stream coming from the pee-hole and the water is definitely hot. I have shut the engine down immediately each time and no damage appears to have occurred. At first I didn't realize it was just when the jet was on so I took it in. He wasn't able to run the engine with the jet on (old jet, no way to get water to pump in his shop) so he changed the thermostats. He said they looked pretty fouled so he changed the head gaskets. I brought the prop unit in and we switched them and it ran like a charm without overheating so we thought the problem was fixed.

Unfortunately, just recently, I put the jet pump back on and the first time I fired it up it overheated. I have not changed the water pump impeller because it was fairly new and it visually looks fine. The only other thing that is different that I can think of is I lost the screw that goes in the hole that would normally hold that anode thing that attaches on the underside of the stabilization fin above the prop. As a result, that triangle-shaped plastic piece that goes over the hole from above got blown out. Now, especially when the jet unit is in reverse, I get a 15-foot high stream of water shooting up through that hole. It looks like a jet-ski. I wouldn't think that would affect anything but I thought I'd mention it. Sorry so long. Thank you for any thoughts.

[boats.net]

It would almost have to be a water pump problem or the jet drive not deep enough in water which is unlikely.

[bullspoonie]

I will change the water pump out. I probably won't put the jet back on until this fall but I will let you know if the problem is fixed or not. Thank you.