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2005 Kymco Venox - fan / thermostatic not engaging (but tested as working)

Posted: Fri Jul 27, 2018 2:40 pm
by kevinamun
Hello motorcyclists,

New member here and hoping someone can offer some help.

I have a 2005 Kymco Venox 250 and it overheats. I'm at a loss on how this can be. The bike has just 7,000 miles on it and it seems the cooling system is working but continue to experience troubles.

One obvious problem is the fan never turns on and initially I thought it was either a defective fan or thermoswitch. At one point it did turn on but no longer engages.

In testing the fan by hooking it up to the battery direct, it works. It also works if I run a jumper between the two wires that connect directly to the thermoswitch telling me that the wiring itself is good and there aren't any broken lines.

In testing the thermoswitch in a pan of boiling water with a multi-meter, the switch does "engage" and open the circuit once the sensor is dipped in the boiling water. (I have two of these thermoswitches - both tested ok with the same results).

The water pump appears to be operational as I see the coolant in the radiator 'tumbling' around when I look through the fill cap hole and the coolant seems to be traveling through the radiator, thermostat etc as all the hoses feel warm/hot.


During my testing, what I am experiencing is after several minutes of running the bike, even at idle, eventually the temperature light will come one. The fan never engages. If I see the light come on, I immediately shut the bike off and put a jumper on the thermostatic switch wires to engage the fan in the hopes of quickly cooling it down. At times, the coolant has gotten so hot, it comes out of the radiator cap.

How can the bike overheat enough to cause the warning light to come on and cause coolant to escape out of the cap from the heat and pressure but it's not hot enough to trigger the thermostatic switch to engage the fan (the sensor is submerged in coolant)? This makes no sense to me.

As I said, I have two thermostatic switches (I just bought a new one thinking with 100% certainty it was a faulty switch). Turns out, my old one worked fine.

Very confused.

Has anyone experienced something like this?