Yamaha 40 overheating control test?

[stringbag]

I have a 1984 Yamaha 40HP (twin cylinder)in tidy order. Engine runs well but the overheat sensor and engine rev limiter cuts in regularly as soon as the engine gets a few minutes running at more than 1/4 throttle.<br />Engine temp feels okay (the touch test on the block), water pump impeller is new, tell tale pressure is great even at idle, so I doubt I have a cooling water problem. Maybe wrong with this though...<br />My thought is I have a faulty engine rev limiter and temperature sensor. I have no idea how to test this to check it out. <br />Any ideas and suggestions welcome.

 

[Jammu]

Re: Yamaha 40 overheating control test?

Take the thermostat out an try to run it without it. If it works now, then change the thermostat.

 

[jim dozier]

Re: Yamaha 40 overheating control test?

If the engine isn't overheating as you suggest, removing/or replacing the thermostat won't help. Besides, you can test a thermostat in a pot of water on the stove with a cooking thermometer. What you really need to do is confirm that the engine is or is not overheating. Infra red thermometers are available for a reasonable price at Radio Shack. You point them at the cylinder head or anywhere else. Or you can get hold of a heat stick crayon from a dealer and mark the engine for temperature. <br /><br />If its not overheating, you could replace the sending unit for the alarm. They do sometimes give erroneous alarms. You should go to the bottom of this web page and buy a manual if you don't already have one.