Bizarre T-STAT activity

hotrod1 said:

ST1100Y, Will check and clean the radiator itself, what is your implication regarding a new water pump?..I'm pretty sure it's the original

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Never had an issue with the rad yet, but it seems worth checking if either sides, air or water have restricted flow (had that on my Toyota once; temps raised slightly above normal while requesting power from the engine at 100mph, temps dropping instantly when going like 60 or less... turned out that corroding fins had squeezed the water passages, reducing the flow, enough to raise the temps when more fuel is burned)

There have been reports on this forum about corroding pump-impellers; wrong/never replaced coolant/use of tap-water can cause the blades to rust away...
Such should be somewhat visible when starting the cold engine and peeking into the open radiator neck while its warming up (never whack the throttle while radiator cap is removed!)
Already in idle the pump should blow a well noticeable stream of water blown through the small bore in the t/stat plate; once the t/stat starts to open a significant swell of coolant should get visible... (stop the engine then or quickly place the cap back on, as otherwise the expanding coolant will cause overflow...)

Had two ST1100's and one kept "Over heating". To test things, I put a thermocouple beside the fan switch on the "No problem ST" and started the bike and recorded the temp and time to the fan coming on. Did the same with the ST that overheats. Got the same result?? I then suspected that the gauge was the problem. Found the wire to the thermostat housing switch was all corroded. Cleaned it up and everything was back to normal. Simple fix.

Before finding the corrosion I also changed the thermostat, fan switch, thermostat switch and over flow hose and kept getting the supposed "Overheating issue" and expensive lesson.

Look into the connector to see if its clean.

Great information, I will check all the above. Thanks