my 1989 30hp yamaha is overheating, alarm goes off, motor is pissing strong, i check my thermostat \, it is missing, Could this cause to run hot?

[sambrigman]

is there any other reason that causes it to get hot?

 

[dingbat]

is there any other reason that causes it to get hot?

A “strong” pisser is a meaningless measure of flow through the motor.

Yes, not having a thermostat will cause an overheat

Heat transfer is a delicate balance between flow and surface area. Throw either out of balance and you have problems

 

[Scott Danforth]

^+1.

 

[brodmann]

Replace your water pump impeller. How's the motor running? A lean condition will cause overheat also.

 

[mike_i]

dingbat is right on. When was your water pump replaced last? How long and why no thermostat?

 

[sambrigman]

Replace your water pump impeller. How's the motor running? A lean condition will cause overheat also.

motor starts good idles great runs perfect at high speed for 4 or 5 minutes, then breaks down and will only go idle speed

 

[sambrigman]

dingbat is right on. When was your water pump replaced last? How long and why no thermostat?

i just got this motor, i did put a new propeller

 

[QBhoy]

You sure it’s an overheating alarm ? Could it perhaps be the autolube tank low ? Do you have a red light on the front of the engine ? Or is it alarming through the dash/remotes

 

[99yam40]

There is a good chance that the water cooling passages are plugging up in a 34 year old motor due to mineral build up, so someone removed the stat to try to solve the over heating, but it did not help.
you can either run some marine descaler thru the motor for a few hours or take the motor apart and manually clean the cooling passages