Hey guys... I'm new here and new to trials bikes.

I bought a 99 Montesa Cota 315r and it is over heating.

I tested the fan (shorting the plug and starting the bike) and the fan spins fine.

I tested the thermo switch and it's fine too.

What else should I check??? Any ideas of what could be wrong???

Last time I rode it I THINK I noticed the fan spinning kind of slower when it overheated but I shut it off fast so Im not really sure.

I'm using regular 50/50 coolant mix.

Please help... I wanna go and play!

Edited July 4, 201313 yr by perkgana

if you join the 2 thermostat wires together the fan will run constantly then start the bike and check out the fan speed could be worn out or there is something trapped in there

you need to determin if the fan is spinning slow or not ,(it will spin slower at tick over ) might pay to try a voltage check with the fan running , you have checked the power sauce for the fan and the switch and found to be ok ( how did you test switch ) so if these are ok you only then need the hot coolant to pass the switch to trigger it if this isnt happening check the coolant pump is pumping or cooling system is circulating with no blockages , if the system is pressurising and blowing coolant out the rad top you could have a head gasket problem or faulty cap ,also check the air can pass through the radiator and direction of fan is correct ,a very lean running engine or sticking brakes can cause over heating

My fan makes enough noise that I hear it over the engine when stopped. So I would expect your fan to also be noisy if it is running at full speed.

Overheating could also be a bad impeller in the pump.

When starting a cold bike I use the fan turn on as an indicator that the engine is warm, usually happens in just a few minutes.

I have 2 blades missing on my fan but it still seems to work fine. Do you think I need to replace with a new one for 50 I only use the bike as hobby riding and not intensivly. The broken blades are opposite each other so I think it's balanced.

I have 2 blades missing on my fan but it still seems to work fine. Do you think I need to replace with a new one for 50 I only use the bike as hobby riding and not intensivly. The broken blades are opposite each other so I think it's balanced.

I would replace the fan. It isn't worth the risk of damaging your (very fine) engine

Hi guys, my fan isn’t working either, I found a green wire sticking out of the radiator cover. Removed the cover and the short wire fell out with a ring connector crimped to one end and the other end looked clean cut. Can’t see anything obvious, any help appreciated 😊