My jet ski is used and well ridden in fresh water only; l keep up on as much maintenance as l can, and l replaced the thermostat recently and change the plugs, new oil, etc. every season. My overheating sensor is going off, l inspected it and the wire but it looks ok.

l started it up, dry out of storage like l do every year, and it fired right up but the tone sounded right away, and l only had it running less than 5 sec. The tone sounded last year in the water, l would run it, fairly hard, and then l would let it idle and the tone would sound and l would shut it off and it would be hard to start...l replaced the thermostat but found out last year it did not resolve the problem. The tone still went off when l had it idling in the water but only after it was started for a minute or so. What are some possibilities that would cause the sensor to go off with my situation?

l am thinking that some kind of water pump in the engine is on its way out...

Polaris is seem to have that problem a lot

inspect the coolent hose from the impeller housing to the engine it is cooled by the water from jet drive be sure you have good water flow that no trash has plugged the line can not remember if polaris has a water flow sensor or just an overheat sensor but sounds like you have a flow sensor at idle not making enough pressure to push water by what evers slowing down flow of water to engine remember to allways look for the simple stuff first good luck

Jet skis do not have a water pump to cool the engine. They rely on the propulsion pump AND FORWARD motion to push cooling water through the system. In other words, they r not made to sit & idle.

Polaris is known to have oiling issues which can make one run hotter than normal. Premix fuel resolves that problem.

There is also a bypass cooling system & pop off that may be sticking causing an overheat. But l really think excessive idle time is ur trouble.

You can go here (a nice site) & see the cooling diagram for ur ski; http://216.37.204.206/Mcmart/Polaris_OEM/PolarisPWC.asp?Type=12&A=16

Mkae sureit is FULL of water. air pockets in the engine will cause the sensor to react even when it is not hot. Check a maintenance manual on proper filling of the colling system so you avoid air in the system.