alarm problem and dont know what to do

[nwelch]

I have a 1996 90hp Yamaha and having alarm problem. When i first got it i couldn't take it over 3000rpm without the heat alarm sounding. So i took it to the shop the thermostat was bad and the water pump blew apart. So i got them replaced. It fixed the problem sort of! I could run between 35 to 3800 rpm and then the same problem. Alarm comes on and kick the motor into safety mode. So i took it to my uncle (who is a mechanic) he took it apart and cleaned it. It was pretty gumed up. So yesterday i put it in the water i got to 4000 no problem. But at 5 grand problem started again. I was told that this moter should operate in the 5500 range but i cant find Yamaha recommendations on it. Is there something i am not doing or am i running to high of rpms. This problem is going for a year and is starting to get tiring.

 

[99yam40]

are you sure it is an overheat alarm going off now?
Do you have gauges that will indicate this?

Yes it should be able to run 5500 at WOT without an alarm sounding

did they replace the water pump housing along with the complete kit

 

[nwelch]

I dont have any gauges to let me know. As far as i know the housing was replaced. And i premix my gas because i dont have an oil feeder. What other alarm could it be? I also had alot of weight on my boat. Could that have been a factor?

 

[Silvertip]

Thermostat stuck Shut causes overheat at low rpm. A malfunctioning bypass valve causes overheat at high rpm. No mention of servicing this was mentioned. I'm not positive that engine has one but expect it does.

 

[nwelch]

Ill look into that thank you

 

[99yam40]

a stuck closed thermostat will cause an overheat at any RPM high or low.

Stuck open pressure relief valve will dump too much water at low RPM where the pump cannot furnish enough water

and block will not fill all the way up causing over heat where there is no water to cool things off

 

[nwelch]

Thank you i herd about the prv. I will check it out.

 

[pete j]

I tried running to much prop before with same results well somewhat. Might be a thing to check