Heat Alarm sounding (120 Force outbourd)

[loft006]

My 1999 120hp Force Outbourd motor heat alarm goes off at 'no wake speed'. The impeller has been changed professionally a few times in the last couple of years and the heat alarm still goes off. No thermastat. And I tried adding more oil just in case I was burning to lean and that just added more smoke. Alarm still goes off at slow speeds. If I excelerate and create a wake then the alarm goes off. Also, the water coming out the back seems very hot at idle and slow speeds. The motor gets too hot to touch.

 

[roscoe]

Re: Heat Alarm sounding (120 Force outbourd)

I'd bet there is a clog/restriction somewhere in the water path. Could be in the water tube above the water pump, or in the block.<br />You can try backflushing the engine with a garden hose, into the thermostat housing.

 

[loft006]

Re: Heat Alarm sounding (120 Force outbourd)

Thanks for the suggestion but the repair shop said that they did flush out the motor, cleaned out the sand, and changed the impeller. I put the boat in the water and 20 minutes later at 'no wake' speed the alarm was going off again.

 

[Downrigger]

Re: Heat Alarm sounding (120 Force outbourd)

Perhaps the lack of a thermostat is the root of the problem. There is a chance that without the thermostat in place there is not enough backpressure to the pump to enable it to pump at maximum efficiency. As with any centrifugal pump, if the discharge pipe is too large the pump just "runs out" and is unable to build enough pressure to pump efficiently. <br /><br />Contrary to common belief, removing a thermostat does not always cause the engine to run cooler. You may need the back pressure to get the pump to push water to the top of the engine. Try putting a thermostat back in and run the engine. <br /><br />You might also put a pressure guage on the engine (or a portable one) and connect it to the 1/8 pipe fitting next to the thermostat housing to check pressure at that point. I believe it should be 8-10# at idle and as high as 20-25# at WOT (not completely sure of those pressures though). Some people just add a telltale tube here and route it through the bottom of the motor cover to check good flow from the top of the engine.<br /><br />Larry

 

[roscoe]

Re: Heat Alarm sounding (120 Force outbourd)

What downrigger said.<br />Put a thermostat in there.<br />Sorry, I didn't catch that in your first post.<br /><br />The water pressures will be lowwer.<br />3-5 at idle<br />8-10 at mid rpm<br />13-16 at full throttle