91' 70Hp over heat, impeller problem FIXED!

[pneitzer]

Replaced the thermostat, inpeller plastic housing, and temp sensor on block.
Same pee stream and water temp as before but NO MORE alarm. I'm guessing the temp sensor or thermostat was damaged when the engine overeheated the first time. Hope this post helps somebody.


My motor had been run a few seconds without the water muffs attached and or course the inpeller blades all broke off. Now the engine overheats only after trolling at 3mph for approx. 10 minutes. Engine runs fine at faster speeds. I've replaced the impeller, removed chunks of the old impeller from inside the water jacket, behind the thermostat and in the water intake chamber in the lower unit. I've replaced the water jacket gasket but it still sounds the overheat warning. The water seems to be warm coming out of the motor but I can't tell if the flow is restricted, it looks ok but it's hard to measure. Help, it's a long trip back to the harbor on Lake Michigan!!!

 

[lexkyboater]

Re: 91' 70Hp overheating, missing impeller tabs

Re: 91' 70Hp overheating, missing impeller tabs

I'm guessing here, and I am a marine newby, but I wonder if it would help to back flush the water pee hole? Or maybe use air? Seems like you might have some restriction possibly somewhere else? Are you sure the thermostat is okay?

 

[pneitzer]

Re: 91' 70Hp overheating, missing impeller tabs

Re: 91' 70Hp overheating, missing impeller tabs

I back flushed with water and air. No change. Seems like the thermostat is working since the water was warm at pee hole. If thermostat was bad I figured cold water would just run thru the water jacket and out the pee hole and never get warm??

 

[lexkyboater]

Re: 91' 70Hp overheating, missing impeller tabs

Re: 91' 70Hp overheating, missing impeller tabs

Do you have the manual and can verify warning horn is working properly? Maybe it's going off at too cool a temp? I think the manual lets you check resistance at different temps if I remember correctly? Also, did you try putting your fingers on the cylinders after running it when the horn is going off? The OMC guys say you should be able to hold your fingers there for about 3 seconds as a good indicator that temp is okay. If you can't get 3 seconds, it's probably too hot. And while you're at it, go ahead and boil the thermostat to see if it opens at specified temp in manual. I think on my 115 Yamaha that's something like 125 degrees.

 

[Ray Neudecker]

Re: 91' 70Hp overheating, missing impeller tabs

Re: 91' 70Hp overheating, missing impeller tabs

If you did not replace the pump housing, there is a high possibility it has warped and not sealing at low rpm's.

 

[pneitzer]

Re: 91' 70Hp overheating, missing impeller tabs

Re: 91' 70Hp overheating, missing impeller tabs

Just received new housing through iboats, I'll install new housing, thermostat, gasket, rubber fitting for bottom of water tube and see what happens. Thanks