2008 Marine Power 5.7 Overheat

[Lad450]

I have an overheat problem that I cannot figure out. I think there's a block in the motor somewhere. I have replaced the thermostat, thermostat housing, head and intake gaskets, risers, water circulation pump, temp sensor and also checked the impeller for the raw water pump and it is in perfect condition. The temperature slowly rises over a few minutes and continues up to 200. I know the thermostat is opening because I have bench checked it. I have also ran the motor without the thermostat in and it takes a little longer but eventually makes it up to 200 and I pulled the throttle back at that point to let it come down to just below and then it would stay there while at idle. Anyone have any advice or recommendations?

[freeheel4life]

Is there a chance the wrong impeller is in it?? Also double check all the inlet hoses from thru hull to impeller pump housing. Make sure hoses aren't collapsing on themselves under suction, also make sure you aren't sucking air in on the suction side somewhere. Also, there may be a small chance that the SENDER is the problem and giving you high readings... can shoot it with IR temp gun and double check. Also did an impeller get roached and send pieces through??
Just some quick thoughts

[Jetdriver]

Another couple thoughts, and pardon me as you’re obviosly mechanically inclined if you’ve done all that yourself, but sometimes the easy stuff escapes ya.

-Are you test running the boat on a fake a lake and if so is it just at idle or are you giving it throttle? A garden hose really doesn’t provide sufficient cooling water at much past idle power.

-is it spitting water out the exhaust?

-Maybe a blockage in your transmission cooler, I pulled a bunch of crap out of the front of mine one season. There’s a screen type deal in the front (drive) side of it.

-I’d trace the intake hose all the way from intake grate, through drive, tranny cooler, raw water pump housing, all the cooling hoses, thermostat housing, through to the exhaust. First make sure they’re all on and tight then I’d start taking hoses off that you can and verifying they’re clear.
I’m guessing something’s blocking water flow somewhere.

[boatwakes]

Does the alarm ever sound? Use a laser thermometer to verify thats actually the temp at the sensor. If the alarm doesn't sound (it's a separate sensor than the gauge sender) its a bad sender or gauge. The laser thermometer should read about 165.