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

[kevinamun]

Hello Venox 250 owners,

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.

One obvious problem is the fan never turns on and initially I thought it was either a defective fan or thermoswitch.

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.

So confused!

[CROSSBOLT]

Thermos witch that "engages" and OPENS the circuit is not the way it should work. It should CLOSE the circuit when the set temperature is reached. I may be misunderstanding what you meant but a switch that is OPEN will not conduct current to make the fan run. You proved the switch was faulty when you jumper wired the switch terminals and the fan operated.

[kevinamun]

Hi Karl,

Thank you for responding.

Much appreciate you explaining the circuit terminology as I wasn't using it correctly in my initial post.


To clarify:

When I test the thermostatic switch with my multimeter for continuity,  it results in a "1" (Open Circuit?) at room temperature which I believe is expected.

Even when installed on the bike and letting it run to get hot, the circuit never closes though to engage the fan. It remains open to the point where my bike will overheat and coolant will come out of the cap if I let it run long enough.

In testing the switches (I have two of them as I purchased a new one assuming the old one was bad), by dipping them in a pan of boiling water and measuring the continuity, within 5-10 seconds of having the sensor in the boiling water, the thermostatic switch closes the circuit automatically and my multimeter will suddenly emit an audible tone and show a "0" on the screen. I assume this means the circuit is now closed and the fan would turn on?

UPDATE: After re-bleeding the coolant through the thermostat airline to ensure their weren't any air bubbles (as recommended by my KYMCO service manual), I ran my bike for about 20 minutes. The hoses seemed really hot especially around the water pump and those leaving the thermostat housing. Eventually the temperature light came on, and surprisingly within 20 seconds, the thermostatic switch seemed to close and the fan started to run (this is the first time I have been able to get it to close the circuit by itself while installed in the radiator). For fear of completely overheating my bike, I did shut it off since the warning light was on but let the fan continue running for a few minutes to continue cooling the radiator. I suppose this means the thermostatic switch is doing what it's supposed to.

That said, before this persistent overheating trouble started, the fan would cycle on and off often both at idle and while driving. Generally within just a couple minutes of starting my motorcycle, the fan would kick on. Now, it seems like it kicks on too late and not "feeling" the same coolant temperature that the rest of the system is so I still have a problem.

I wish I knew more about motorcycles. The Kymco Venox's are a difficult bike both in finding parts and a shop knowledgeable enough to service them.

[CROSSBOLT]

OK, you are doing fine! That explanation was the best! You have the right procedure and you are using and interpreting the meter correctly. Your thermal switch is not turning on at the right temperature. Most thermostats and thermal switches have the temperature stamped on them somewhere. If not then you have to go through the time consuming method of slowly raising the temp of your water pan while watching your meter. It is easy to fall asleep! What should the temp be when the switch closes? Since I don't know I would guess (yes, GUESS!) 200 F. Thermostat should open about 190-195 F and the fan kick in about 200 F. Yep. That's my story and I'm stickin' to it! Maybe there is a service manual somewhere that puts factory numbers on this...

[kevinamun]

OK, you are doing fine! That explanation was the best! You have the right procedure and you are using and interpreting the meter correctly. Your thermal switch is not turning on at the right temperature. Most thermostats and thermal switches have the temperature stamped on them somewhere. If not then you have to go through the time consuming method of slowly raising the temp of your water pan while watching your meter. It is easy to fall asleep! What should the temp be when the switch closes? Since I don't know I would guess (yes, GUESS!) 200 F. Thermostat should open about 190-195 F and the fan kick in about 200 F. Yep. That's my story and I'm stickin' to it! Maybe there is a service manual somewhere that puts factory numbers on this...

OK, you are doing fine! That explanation was the best! You have the right procedure and you are using and interpreting the meter correctly. Your thermal switch is not turning on at the right temperature. Most thermostats and thermal switches have the temperature stamped on them somewhere. If not then you have to go through the time consuming method of slowly raising the temp of your water pan while watching your meter. It is easy to fall asleep! What should the temp be when the switch closes? Since I don't know I would guess (yes, GUESS!) 200 F. Thermostat should open about 190-195 F and the fan kick in about 200 F. Yep. That's my story and I'm stickin' to it! Maybe there is a service manual somewhere that puts factory numbers on this...

Thanks Karl.

According to the service manual, at 90 (+/-2) degrees Celsius (192-196 degrees Fahrenheit)  the thermostatic sensor should close the circuit and start the fan. While I did not use a thermometer when I tested both the old and the new thermostatic sensor in a pan of boiling water, it would seem strange that both the old and the new switch exhibited the exact same results where, after dipping the sensor into the boiling water, within seconds the circuit closed. I may have to buy a good thermometer and see if they are closing the circuit within the temp. parameters specified though.

Up until this point, I have not tested the thermostat itself as it would require me to open up the housing and if I do, I believe I would need to replace the o-ring. As parts are hard to find and I usually end up having to wait 2 weeks for them to arrive in the mail, I haven't yet decided if I should look at the thermostat.



Lastly, I don't mean to ask a silly question, but in combing over my bike, I noticed there is a hose that is hanging and not connected to anything. If I were to sit on my bike, it is on the right side. I have attached two photos. The first shows where it's connected to, the second photo shows how it hangs. Is this normal or is it supposed to plug into something. I didn't see a place that it should go to and there isn't sort of indication that was ever plugged into anything (no indentations indicating a hose clamp was used). Any idea what this is?

[CROSSBOLT]

Have not the foggiest....

[hypophthalmus]

So the fans are coming on after bleeding it... I assume this means you got some air out. Maybe there's still some left?

I wouldn't suspect the thermostat since the radiator is apparently getting hot.

[hypophthalmus]

I don't think that coolant coming out of the radiator cap is normal, and when it's overheating. Maybe the radiator cap is bad.