over heat alarm

[shoemake]

I have a '99 vx225 that I am having trouble with this alarm going off. It only goes off while motor is in the lake. Cant get it to go off while I have hose hooked up to it. Sometimes it goes off as soon as I turn ignition on and sometimes it will wait a few minutes before going off and sometimes it wont go off at all. When it dont go off the motor runs normal.
Things i have checked:
*changed out pump impellar
*took thermostats out checked for operation and cleaned with lemon juice
*ohmed out thermal couplings?? that are on top of thermostats by heating them up with hair dryer.

I am open for any other suggestions....

[rodbolt17]

no thermocouples on that engine.
there are two thermoswitchs and a coolent temp sensor.
hairdryer wont heat them enough.

if equipped a water detect can trigger an alarm.
a crank signal and a stop signal can trigger an alarm.
low oil level in the engine tank can trigger an alarm.
low battery voltage at the ECU can trigger an alarm.

thermoswitchs should read infinite ohms unit they hit about 185*F then by 194*F they should read 0 ohms.

[99yam40]

never mind I see Rodbolt has already taken care of it

[shoemake]

would any of the info u gave me cause the "over heat" light on my dash to light up and cause buzzer to go off? once the alarm goes off its like it distorts the timing and will not get over about 2000 rpm. it almost acts like i have a switch that is not working right. the motor does not seem to be getting hot cause its not so hot u cant touch it.

i really just checked for some resistance through those thermoswitches (ha-ha). wasnt sure what they were, thanks! when i hooked them up to the meter they read 0 ohms. as they started getting hot, they started showing some resistance. (not your ordinary hair dryer-heat shrink gun)

[99yam40]

you never said that you got an indication on the tach that it was a over temp alarm every time, that would have been good to post 1st up, is that even when you first turn on the key some times with out the motor running?
If so you may have a wiring problem, or if you said you had 0 ohms while cold on one then that switch has a problem.
As Rodbolt said "thermoswitchs should read infinite ohms until they hit about 185*F then by 194*F they should read 0 ohms"

[shoemake]

sorry for the misunderstanding. should have mentioned over heat light in my description and not just an over heat alarm in my subject heading. it has always been the over heat light/buzzer that has been giving trouble.
on the other hand, the temp light has only come on once or twice as soon as i turn the key on without motor running. for the most part, the motor has to have idled for a few minutes. why does this problem just show up when in the lake?

[99yam40]

sorry for the misunderstanding. should have mentioned over heat light in my description and not just an over heat alarm in my subject heading. it has always been the over heat light/buzzer that has been giving trouble.
on the other hand, the temp light has only come on once or twice as soon as i turn the key on without motor running. for the most part, the motor has to have idled for a few minutes. why does this problem just show up when in the lake?

And what do you not understand about the 0 ohms and infinite readings on the ohm meter. Not sure on your motor but on mine 0 ohms means the motor is overheated and the alarm is going off. If the motor is not hot or even running then I would suspect that switch

[shoemake]

so basically the switch is open until it reaches 185*F to 194*F then it closes and reads 0 ohms and alarm goes off, right?

[axolotl98]

From your description, it seems very probable to have one or both malfunctioning thermoswitches.
I would replace them and check again. They are not a very costly part of the engine...

[rodbolt17]

basically?
yep thats how a thermo switch works.
its ON or its OFF.
should be no inbetween.