Engine alarm going off...HELP!!!

[HOOKN UP]

I have twin Yamaha 200's. I am having an issue with my one of my engine's temp alarm going off. This only happens when I run it full throttle. I have used a temp gun and when the engine's alarm goes off it is only running at 119 degrees. This is the same temp as the other engine. I have tried to switch the sensors on the two engines thinking that there may be a problem with the sensor but that did not make a difference. Does anyone have a clue as to why this alarm may be going off when it seems the engine is running fine. This past weekend, I took the sensor off the engine and ran it over 100 miles with no problems. I would like to have the sensor on the engine in case it does overheat in the future. Any help would be appreciated.

[Grady23]

Are you taking the temp reading at the same place as the sensor is installed??

[HOOKN UP]

Yes I am

[Rockonafly]

I am not sure about yamaha but my mercury had a similar problem and it turned out to be the alarm module. Mercury had a troubleshooting guide in the shop manual.

rockonafly

[FinaddictMike]

I'd bet your money it is the alarm module. They are vulnerable to heat and go bad when no problem exists. I put my second module on with finishing washers between it and the block to try and protect it from the heat. At about a $160 a pop I would like them to last but while they can easily be by-passed I want them to work. You can run a diagnostic to check it and if you don't have the manual I can fax you the check (For a Merc, they all work about the same).

[bucktales]

Just a guess but have you changed out the thermostat lately?

We had a similiar prob on a friends boat, turns out the thermostat was clogged....

How much for a new alarm sensor? I know the thermostats are pretty cheap.

[college fund]

It is possible that you have a fuel restriction, filter, anti siphon valve or carb problem.

[BBCroaker]

Thermostats cost around 32$ but 300 $ to installi on a Jhonson motor last year.

[Reel Life]

If the engine has alarm modules, swap them since you have twins and see what affect it has. You need to get to the bottm of this before you find you did have a problem. Surface temps don't necessarily tell the whole story. I would check the poppet valve (mercury term) or what ever Yammie uses to develop back pressure on the water system which is what determines cooling ability at WOT. Thermostats are actually use to regulate temps under low speed/ low water pressure conditions. Good Luck Mark