Yamaha 40 overheating control test?

stringbag · #1 January 5th, 2004, 10:19 PM

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.

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...

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.

Any ideas and suggestions welcome.

Jammu · #2 January 30th, 2004, 09:56 AM

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

jim dozier · #3 February 2nd, 2004, 04:27 AM

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.

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.