F90 overheat

[Andy.king]

So I’ve got a 2006 F90TLR that I can’t seem to figure out an overheat issue. Motor will run for 10 min or so at idle and alarm sounds. I’ve just replaced with factory parts the thermostat, and pressure relief/poppet valve, entire water pump assembly minus the housing(6D8-WS443-00-00) which I have on order along with the water seal dampener and grommet,. When in gear at a fast idle or running at speed no problems at all. Engine has been in freshwater it’s whole life as far as I know. Didn’t see any signs of corrosion when inspecting thermostat housing or pressure relief housing, just a thin film or dried dirt I assume from water. I’m chasing another gremlin in the tachometer circuit so not sure about the idle rpm’s. Feels like it’s running slightly rough at idle as there is a vibration, not quite like it’s going to die but just rougher than I remember it being when we got it 5 years ago ago. I’ve also not used a thermometer yet to measure engine temps but just seems like it’s a real alarm as it goes off if you give it some throttle and get more water flowing through it. Only have analog gauges, voltage is right around 14 and I’ve checked the regulator/rectifier and it appears to be working correctly. Any thoughts of where to go next before I pull it out and take to shop. Thanks.

[byron.akhavi@gmail.com]

You need to check your water jacket. Debris may have accumulated in the channels that the water pass through as it cools your motor. The exhaust cover will need to be removed and you will need a service manual with torque specs. and removal/install sequence. There is a gasket that should be replaced if the cover is removed. If water flow is obstructed, cooling is impacted regardless of a new water pump and thermostat. Put you motor in a 55 gallon drum with a drain installed. Start it in idle and ensure you have a tell tale stream. Have you flushed this motor regularly?? Yamaha recommends a 15 minute flush via the flush port after each use.

[Dfreddy4]

Any update on this? I am experiencing the same issue after...
1) changing the thermostat (which was recommended due to fuel in oil suspected of being due to running too rich because of running cool),
2) changing the Low-pressure fuel pump (which was the real reason for the diluted crankcase oil),
3) changing the cylinder head zincs (the lower of which was very corroded)
4) changing to water pump impeller (which had disintegrated)
2006 F90TLR 200 hours. In the family for a few years but new to me.