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2007 Waverunner FX HO overheats when idling

2283 Views 8 Replies 5 Participants Last post by  Bmal
I am struggling with an FXHO that intermittently sounds overheat alarms and falls into limp mode when almost-idling for 5-10 minutes after a normal speed ride of 15+ minutes.

When the alarm went off recently I observed exhaust gas (instead of water) being released from the port side pilot hole while idling in the sea. I disconnected the coolant feed hose from the outer exhaust joint. At idle RPM there was no water flowing out of the feed hose. When i revved up a little, there was a reasonable amount of water coming from the hose.

I took the ski out and fed tap water through the flushing port. There I got plenty of water from the port side pilot and the engine would cool just fine. So it seems like cooling water pressure from the jet pump is too low to push water up to the exhaust pipe jacket, and subsequently to the port side pilot at low RPM. Therefore, exhaust gas is creeping up the exhaust pipe's cooling jacket.

What could be a likely cause for this overheat condition?
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I would check for coolant blockage prior to the flushing intake. For instance, the cooling water intake filter (item 15) and its hose.

2007 Yamaha WaveRunner FX HO (FX1100F) Jet Unit 1 | Flemington Yamaha (
I have disassembled and cleaned my cooling system twice. The first time was because salt water was inadvertently left in the cooling system all winter because we were entirely focused on a suddenly broken leaf spring, trailer axle shifting, and tire jam against the frame. The second time was because of the ski being stuck on a sand bar and pulling the ski backwards pushed sand into the cooling system intake

Cleaning - Coolant Path, 1000cc, MR-1, Yamaha - YouTube
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