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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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By way of an update, I have fitted a new water pump seal as well as a new thermostat. I changed the oil three times. Bike was ridden today in total for approximately 4 hours. The fan comes on . There is no overheating despite the high temperatures we are having today. There is no water in the oil.

Thanks all. 


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I currently have 2011 GasGas 280 pro which I have had to fit two replacement water pump kits and again last July I purchased a 2015 water pump hoping that an upgrade would have a longer life but last week end it blew another pump seal, didn't even last 12 months, checked  my log and the bike would have completed about 25-30 hours in the last twelve months and only ridden at club trials in president grade.

Can you tell me if this has been a common problem, is there any warranty from GasGas, would the type of coolant make any difference, I generally flush out the coolant system during replacement.

Also in the last 3 1/2 years I have fitted two new thermal switches, could a bad earth be the problem.


Hope someone can clear up some of my concerns.




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