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Gas Gas 280 TXT PRO 2012 - Fan - intermittent issue and Milky oil

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Bike overheated whilst using it yesterday riding very slow obstacles. I share the bike with another rider so it is running continuously for an hour or so at a time. Coolant overflowed. Noticed fan was not coming on so I revved the engine and the fan came on. I let the bike cool down and then rode the bike again for about an hour and the coolant overflowed again. I went on a fast run and the fan came on. I increased the idle speed and there were no further issues with the fan although the obstacles were ridden a bit faster with more breaks in between bike running.

When I got home I notice the oil had turned  a milky colour (I had changed the oil the day before) and condensation could be seen through the oil sight glass .

So, I have a few questions.

(1) Is the fan or thermostat or rectifier on the way out or has by simply increasing the idle speed, fixed the fan issue ? i.e. was the engine not running fast enough to give enough power to the fan ? or is it that they are not designed to be ridden slowly for such long periods?

(2) Although I have a volt meter I am not electrically minded to know how to check whether it is the thermostat or not so which should I buy first , the thermostat or rectifier? 

(3) should I replace the water pump seal and shaft ? was the seal damaged by the over heating ? or is it a coincidence that the shaft/seal have gone at the same time as the rectifier/thermostat ?

Any help would be appreciated.




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I had the exact same bike and swapping out the impeller shaft and new water pump seal fixed the issue with coolant getting into transmission fluid.

Radiator Fan is controlled by heat temp sensor. When you pull the water pump off, make sure everything looks intact and not missing any parts that might clog radiator or cooling lines.

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