Will overheat alarm cause drop in RPM?

[lazydawg]

I have a 1989 40 HP mariner 6E9L 451969. I have been getting an overheat alarm at WOT and then it begins to sputter. I read in a similar post that a motor goes into a slow mode to prevent overheat. Is this true? Does my motor do this? I have checked the thermostat and poppet and they are fine. Compression is right on the recommended value. Have not checked the temp switch but the water coming out does seem too hot to me.

 

[greasemonkeyozi]

Re: Will overheat alarm cause drop in RPM?

Your carborators may not be set right. You may be running a little lean. Is your tail tell spitting water out good? Does this motor have an oil injector?

 

[greasemonkeyozi]

Re: Will overheat alarm cause drop in RPM?

Another possability is your thermostat could be bad.

 

[Walker]

Re: Will overheat alarm cause drop in RPM?

The obvious possibility is it could actually be overheating and your lucky you haven't done any damage yet. Your motor oesn't have a SLOW mode.

 

[lazydawg]

Re: Will overheat alarm cause drop in RPM?

The tail tell is putting out plenty of water. The water pump is only a couple of months old with not a lot of run time on it. The motor does have oil injection and the thermostat opens wide at around 140F. Thanks for the help.

 

[Walker]

Re: Will overheat alarm cause drop in RPM?

A motor can still overheat with good water flow. Carbon buildup will retain internal heat as will scale buildup in the water passages.

 

[lazydawg]

Re: Will overheat alarm cause drop in RPM?

Will it take a teardown to check / clean the water passages or is there another solution?

 

[Walker]

Re: Will overheat alarm cause drop in RPM?

First you need to determine if your motor is overheating. Check this thread<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=005892 <br /><br />Also do a search of "Decarb" or "Decarbonizing"<br />Ther are a couple of good products that you can use.