4.3GLPEFS SX M outdrive overheating

[ElevatorChad]

I’ve recently re-powered the boat with a new engine. I went with a Edlebrock 4 bbl carb and intake. I have installed a new raw water pump as well. New hoses to the outdrive. On muffs it gets up to around 195 degrees. I just put it in the lake this past weekend. I noticed that under load this thing will overheat. I had an issue with the alarm so it’s disconnected at the sensor on the thermostat. This 2000 Glastron SX175 got up right around 240 degrees before I realized and backed off on the throttle to cool it down quick. It cooled to just under 200. Can someone shed some light on what’s going on. New raw water pump, new thermostat and housing, new risers, new circulation pump, new hoses. Checked everything, it’s all tight and good. Could my outdrive be leaking internally and sucking air? How hard of a task is it to check this and make sure that’s what it is? I’ve got a 15.25x21 aluminum prop on this dude from Hustler. It’s run in freshwater at the lake here in Texas. I’m ready getting exhausted with this thing and running out of ideas. Any help would be appreciated.

 

[alldodge]

Which thermostat was installed?
The fitting on the drive that feeds water, has it been looked at, they can get clogged?

 

[Saline Marina]

One issue is that the muffs are a pressurized water delivery system whereas the lake water pump is a suction system. Its worthwhile checking the gasket between the lower unit and the transom extension (probably the wrong terms here) that it bolts to, but in any case the 6 nuts that you remove and the interface between those two bolted flanges.

Also I'd recommend making sure the thermostat is opening correctly via a pan of hot water on the stove.

Only other thing I could think of would be mixing the hoses on the lake water pump but I don't think it would even work on the muffs if it was backwards. Assume that the engine's own waterpump is turning via V-belt.