OK my neighbor has a boat with a mercruiser 350 and Alfa one. Seems like idling in the water for any period of time, like a long no wake zone causes the motor to heat up. Once it hits about 200 degrees, it sputters a bit and then dies.

We have changed the out drive water pump, engine water pump, butter flies in the exhaust going out the back, plugs, wires thermostat. Anyone have any ideas? It seems to be OK running wide open. Maybe the ignition module getting hot and breaking down? Maybe the out drive water pump bad on install? I am at a loss. This is indeed only a low speed idle issue. Could it be the exhaust manifolds? He pulled the risers and they were OK but didn't take off the manifolds. There has to be a reason that it heats up and dies at idle going through the no wake zones.

Help

TIA
Rob

id check the water intake hose at the transom exteriorfor a pinch when the drive is fully down,,I dont think its a manifold issue because if it was it would heat up faster at high speeds same with any clog type issues

Id be looking on the inake side and since you say it only does it when idleing I assume he trims the drive down comming off plane,

im assuming that the impeller was installed correctly

So Joe... could he check your theory by running the boat at the dock with the drive partially up?

I would find the problem before taking it out again. I dropped a valve trying to chase down a over heating problem.

Yeah, I'm with Joe. I have seen the water hose fold up under the bell housing and over heat the engines before. Take the hose off the t-stat housing sitting still in the water and see how much flow you have. At idle it should look like a half turned on water hose. Rev it up and the flow should go up.

Let us know what you find.

John S.

I got under there and took a look. The hose has been cut in two at some point and a piece of pipe put in it. I told him to yank all that crap out and get the right hose and we would try again.

If not already.....Do a back flow purge of the water intake hoses from the thermostat housing to ensure the oil/fuel coolers have not been clogged up with sand/debri. Take the intake hose off the housing and point it towrds the bilge and start it momentarily to observe water pressure coming in, and to purge any possible sand sitting in the line blocking flow during it's highest demand. Also take a look at the thermostat itself to ensure sand/grit is not holding it partially closed. In fact take it out all together while troubleshooting to eliminate it during the process. This is a common problem usually with a common solution assuming the risers/manifolds are clean.

if that hose is as little as 1/2 in too long it will cause it to crimp so yes take the crap out and do it right