I will say that the impeller has not been replaced since we have had it which has been 8 years or so. That should be replaced I agree but it sure seems to be pissing out a good strong stream. I do have a coil because I initially thought thats what it was but now I am not so sure. I will be changing the impeller also
Yeah 8 years is a long time but if you're in freshwater, they can last that long (and longer). It's good to replace it either way though. But what I was getting at is that the exit stream only tells you that water is getting as far as the bottom cowling area (where the water hoses are). It doesn't confirm that water is actually getting through the thermostat housing and cooling the block sufficiently. Confirming that can be done with a temp gun when the issue happens. If the temp is getting too high, then the thermostat might be stuck, which does happen from time to time. Mine did that last year on my 2011 F50, where it was sticking open and causing an over-cooling condition. Yours might be stuck closed. I would just blindly replace it, since a temp gun costs about as much as the thermostat itself.
Like Sea Rider said, you should get an alarm if it's overheating, but you have to confirm that the alarm works. Not easy to do. But it looks like your service manual is available on manualslib.com. It's a 2002 manual, which should be close enough. That's a gold mine of information. For instance, it says your thermostat should be fully open at 140F, which is lower than average (mine is 158F, for example).
Also, in larger engines, if the thermosensor (aka the cooling water temperature sensor) circuit closes (which happens during an overheat condition), that will trigger the ECM/CDI to cut off spark to half of the cylinders, and you won't be able to rev passed 2000 rpms or so. And you'd also hear a beep from the control box. Your engine only has the one coil, so it would likely shut off completely. What model control box do you have btw? If you're not sure, take a picture.
The manual also says to check that the anti-cavitation plate is between the bottom of the boat and a maximum of 25 mm below it. If it's mounted too high, that can also lead to an overheat condition. It shows a picture of where you should measure that distance. If that was an issue, the engine speed would be abnormally high (well beyond 6000 rpms).
If you have a new coil, might as well install it. If there's no change, then you've basically ruled that out at least. But it still could be an electrical problem elsewhere in the ignition circuit.
