Hi The overheat alarm on my 1990 40hp Yam 2cyl 2 stroke sounds at high revs. Last season it sounded at much lower revs leading me to change the thermostat & sender, which has improved it considerably. It seems strange that it has now moved higher up the rev range. I'm wondering what I should look at next. I have a strong tell-tale which is always cool to feel. My prop is 11 1/8 x 13. My boat is 17ft with quite a heavy semi-planing hull that is designed to max at 18 -20 knots with 40hp. I have been told that a 10 pitch would be better but have spoken to someone with an identical boat & engine setup that does not do this. I run in an area that has strong currents but don't think that the currents plus prop load would make the engine overheat. It must be something happening within the engine. I don't have a rev counter but the engine is running quite fast, a good bit over 3/4 throttle before the buzzer sounds. It is happy to cruise at the pre buzzer level for long periods at planing speeds, then that last nudge of the throttle makes it go off. I can throttle back then get back on the plane again once the buzzer goes off, after a minute or so. Is there any point looking at a new water pump if I am getting a strong tell-tale? Anything else I should try? The engine runs perfectly apart from this.Thanks in advance.Andy
I am guessing somewhat here. Is the tattletale coming directly from the impeller and letting you know if the impeller is working? If it is before the circulation system for the head, there may be some obstruction (salt or some other buildup) within the head passageways themselves. I would look at the thermostat to see if it is working properly and check the passages for any buildups that could cause a blockage....Kev_Alask***
If I hear another, but its peeing a good stream, I'm going to choke someone. That stream is just saying," Hi there, I'm telling you the pump is pumping but its your guess how well I'm working". That stream is cut out of the herd of water before it goes thru the engine and that's why its always cool. As the "rubber" impeller gets older, it becomes less able to push the water at higher speeds and that's why the alarm is sounding. Keep pushing that thing to the limit and the next post will be " why is the compression low in one of my cylinders?"
Listen to the above post!!!!!! How long since your last pump? HereÂ’s an ideaÂ… install a good quality pressure gage permanently, NOT A TEMPERATURE. This will tell you what that little impeller is doing at a set RPM, and when it drops off, or later down the road (lake) when it starts to. Darn important gage if you stop and think about it. Be Safe John
Thanks for the replies everyone.The tell-tale always being cool makes sense as you say. My local Yamaha agent told me to check this. He also discouraged me from having the impeller changed as he said there was little chance that this was the problem. It makes sense that the impeller would be less effective as the motor lay unused for 4 years.I will try replacing this. It's a total pain having to return motor to shop for repair I initially suggested. Maybe I could tackle it myself?Cheers
If that dealer really is a Yamaha dealer, then Yamaha needs to slap him upside the head. Yamaha reccommends changing the impeller every year but even I think that's too soon. Impellers need to be changed every two years. The first question out of his mouth when you said you was overheating should have been, "when was the impeller changed?" If your answer was two years or more, the impeller should have been changed first off.
Capt KenI have the Yam service manual. It looks quite easy to change the impeller. Put unit in reverse, undo gear linkage, drop lower leg, take cover off the impeller & change it. Is it that easy, or is there anything I should be careful of? Is there is specific type of marine grease I need to lube the new impeller and how much should I put on. I would rather take it to the Yamaha shop but would probably loose the rest of the summer waiting for it to be done. What is a realistic time for a outboard mechanic to do this job in?CheersAndy
Yamaha 40 high revs buzzer sounding.
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