It could be an airlock somewhere maybe find the highest point the coolant comes out of the head loosen the hose then pump a hose further down the engine see if air bubbles come out or see if you can find a bleed screw on the barrel,usually a crosshead with a copper washer. Definitely should not have the fan running while riding along with air flowing through the radiator fins...check for debris in those fins too,mud or dead insects clogging the airflow...could be a faulty fan switch. Worst case could be a head gasket issue but if not losing coolant that is unlikely.
Air lock sounds favourite to me,your dealer should be able to plug in a diagnostic reader to eliminate some of the obvious things...
Good luck finding the issue....

 

Thanks for the information. There must definitely be trapped air somewhere high up in the engine. I don't have any dirt in the radiator or the fan. Everything is clean because I've washed it. And the fan operates at its normal speed. I also don't add antifreeze, so the head gasket doesn't have any issues either.

 

Good news! The problem was found. I drained all the antifreeze from below the screw on the pump in front of the gear lever. Also, the motorcycle was placed on the side stand. I removed and checked the thermostat and it was working normally. Then I filled the radiator with deionized water (about 1.5 liters). At first I had the screw on the pump open until all the antifreeze was cleaned and then I screwed it in, and filled with water. I started the engine with the radiator cap open. I waited at idle for about 10 minutes until the temperature rose and the thermostat opened and the fan started working. As soon as the thermostat opened, bubbles came out of the radiator water inlet for about 5 minutes. And I turned it off. Since then, it has come on every 1.5 minutes and worked for 35 seconds. Also, the thermostat cover had a temperature of up to 93 degrees before the thermostat opened, and when it opened, it dropped to about 87 degrees. Then I took a ride at 30-35 kilometers steadily in 3rd gear and the temperature had 2 bubbles and the fan was not working. Whereas before I was going at 80-90 and both the 3rd bubble and the fan came on. So I assume that the bypass may not have been suitable and air remained trapped. Now I'm going to put antifreeze mixed with water again. I think it's better now than before I got it. Thanks teddybear for your help...

 

Very welcome...That is good to hear sound like a fairly simple fix too,one we all like... enjoy the bike i always liked the Trk 500x nearly brought one then the 702x came out and I like that too so did get it and love it..