Boat started to overheat - Why?

[Wake Havasu]

It's pumping water and there is coolant in the tank.

What else would casue the engine to heat up?

It's a 6.0 Gm Vortec.

[Gardyloo03]

Your thermostat may have broken.

[lee]

Is your impeller in good shape? With the 6.0, you still suck in lake water to cool the heat exchanger for the closed cooling system.

[Wake Havasu]

Impeller replaced, Thermostat actuates all lines clerared.

Sucks and spits water.

Yet still overheats.

[kko]

are you running boat in the lake or on a garden hose?

[Wake Havasu]

Originally posted by kko
are you running boat in the lake or on a garden hose?

Both

[kko]

i would repalce that thermostat it may open slightly so you think its working but if it does not open all the way or close all the way and can cause this problem. is it a slow gradual overheating or does it overheat in just 2-3minutes. does it overheat while at speed or just at idle? we had a 5.7 with closed cooling that the guy overheated because he starved eng. of water. repalced impeller and the boat still overheated it took it a while though a slow gradule over heat. i thought the stat was working what you call "acuates". as i saw coolant moving through the heat exchanger. but it still would overheat so i put a new thermostat in and it fixed it. i would replace your thermostat. its really the only thing besides blown headgaskets that can cause overheat if you are indeed pumping water through engine.

[Wake Havasu]

Overheats qucikly and shuts down to idle.

[chpthril]

I would also look for trash/debris blocking the raw water supply to the heat exchanger. Just like air flowwing across an automotive radiator, if you block the air, the engine will run hot.

[kko]

chpthril has a good point (first time for everything LOL just kidding) you might want to check for blockage. pull the hose off the inlet side of trany cooler thats were the trash ends up most of the time.