92 115 Yammy 2 stk - heat alarm > 5000rpm

[scottoz]

Hi all - I had a new impellor, thermostats and water pump kit put in about 13 months ago. I suppose it might be time for a change, although not used more than 6 times since, because she is suddenly sending off the alarm above 5000 rpm when at that level for more than about 30 seconds. It seems to cut a few cylinders and after about 30 secs at idle I turn it off and back on and she is fine (provided I dont again exceed 5000 rpm). Is it worthwhile pulling the covers off and cleaning the galleys. Could it be that the diverters need replacing (never done to my knowledge). Could it be water pump. Or all three?. What is more probable and what would you do first - I was thinking water pump kit and impellor. Cheers.<br /><br />PS. I posted a while ago about stalling between moving from the forward gear to reverse and Rodbolt suggested cleaning the float bowls. I did that - full of crap - and it now runs like a dream at idle. Thanks Rodbolt.

 

[WillyBWright]

Re: 92 115 Yammy 2 stk - heat alarm > 5000rpm

I'll bet the cooling walls on the block are scaled. That insulates the metal from the water and the water doesn't carry enough heat away. If it's a freshwater boat you might get away with removing the heads, laying them flat on their backs, then filling the cooling cavities with vinegar and letting them soak. That'll dissolve lime scale. Not sure about saltwater scale. It doesn't address the scale on the cylinder walls, but it should help with that alarm situation. Removing the heads will also expose the cylinder walls and you can determine a course of action from there. So at this point, if the water pump is working fine and new thermostats did no good, pull the heads.

 

[Ray Neudecker]

Re: 92 115 Yammy 2 stk - heat alarm > 5000rpm

Pulling the heads will also allow you to be sure the head gasket is not leaking or the water passages restricted by gravel. Even though poppet valve problems are often associated more with low RPM problems, it would be a good time to service it. A compression test also should give an indication if a head gasket is leaking.

 

[scottoz]

Re: 92 115 Yammy 2 stk - heat alarm > 5000rpm

thanks all

 

[Osprey]

Re: 92 115 Yammy 2 stk - heat alarm > 5000rpm

This past year I had an impeller on a Yam 175 that lasted less than a year. It had a white plastic molded in center bushing rather than Yamaha standard metal. I believe it was an aftermarket non-Yamaha part. The drift-key slot in the plastic bushing had torn out so that at low to medium RPM's the impeller would turn and pump some water, but at higher RPM's the impeller shaft would spin inside the impeller causing overheat.

 

[j_jtaylor]

Re: 92 115 Yammy 2 stk - heat alarm > 5000rpm

I had the same problem with a 92-115hp, and I ended having to rebuild the whole motor!!! Turned out water had been getting into the crank and stuffing everything around, hope this is not your problem!!!