What could cause this overheat alarm? johnson 115 1995

For several yrs Ive had an intermittent overheat problem. The only time its happened is when I start up the motor on the muffs in the driveway after it hasnt been run in a long time. After idling a few minutes, the warning horn would go off.

Never had an alarm while actually operating the boat on the water. Water pressure gauge shows good pressure.

Sometimes I tapped the thermostat housing with a hammer and metal rod, and it would go away. I figured I had a sticking thermostat, but since it only happened once in a while, I lived with it. Especially since changing the thermostats on this motor is quite difficult.

Well, I changed the thermostats today, and the problem still occurred...once.
I started the motor, the thermostats opened and hot water came out the exhaust ports above the anti-ventillation plate. But after about 5 minutes the tell-tale got real hot, and the alarm went off.

I restarted it about 10 minutes later and let it idle for 20 min+ and it didnt happen again, the telltale stayed cool too.

What gives, the impeller is only ~2 yrs old but has maybe 10 hrs on it. I have ingested mud and silt once or twice, but not sand. In any case, the water pressure is fine.

Re: What could cause this overheat alarm? johnson 115 1995

On a flushette/hose, you do have the water turned on full force as it should be?

Re: What could cause this overheat alarm? johnson 115 1995

Yes, its open plenty.

Re: What could cause this overheat alarm? johnson 115 1995

Well, replaced the thermostats and took the boat out. Idling out of the no wake zone near the dock the warning buzzer went off. I noticed that at low idle ~800 rpm I had maybe 2 psig water pressure- kind of low.

I waited for motor to cool off, then restarted and got up an went. At ~1100-1200 rpm I had 5 psig, and at 4500 rpm I had 20 psig. No overheat alarms while running around all day, I took care not to idle long at an rpm that gave me less than 4-5 psig.

Today I replaced the water pump. Not just the impeller, but everything. The old impeller was fine , no noticeable wear at all. The baseplate was slightly scored though. Maybe this had something to do with not building enough pressure at low rpms.

On the muffs I now get 6 psig at ~1000 rpm , slightly more than before. Seems more water coming out the exhaust too. I hope this fixes the problem.

Re: What could cause this overheat alarm? johnson 115 1995

I had the exact same problem with my 1996 Rude 115 HP. I just paid $850 to have a new water pump and new gaskets put in. Problem still there. The dealer who did the work said not to worry about it , sometimes the muffs used in the driveway just does not allow enough water to enter the motor, it seems to run fine when out in the bay. Go figure.......

Re: What could cause this overheat alarm? johnson 115 1995

I was having the same problem. I replaced my water pump and boy what a difference it made with the tell-tale stream. Also when I started it in the driveway on muffs it puked a bunch of sediment out the exhaust. The motor was overheating in a matter of a few minutes on muffs, but after running about 10 minutes I could still hold my hand on the heads for a minute before it feeling hot whereas before I couldn't keep my hand on the head for 10 seconds. My water pump also looked ok. ONly reason I was replaced was the oring that goes on the water pump housing was stretched out to be about 2 inches longer than it's supposed to be. Figured since that was in such bad shape wouldn't be a bad idea to just rebuild the whole thing and boy what a difference it made. anyways, hope you get things worked out.

Re: What could cause this overheat alarm? johnson 115 1995

Be careful?.water pump impellers can ?look fine? and still be way out of it?s performance tolerance. I operate in saltwater and change it every other year whether it shows symptoms or not. $45.00 for a water pump kit vs. $2,700.00 for a re-built power head is not a hard choice for me. Frank - I don?t work on boats for a living but any alarm in any condition is NOT a good (or normal) thing.