Today I had an experience that was kind of unexpected, and I'm hoping someone can give some clarification.

Previously my automatic fan switch had been broken. Today I got around to replacing it. When I pulled the old one out, probably a few cups of coolant drained out before I could install the new one. To compensate, I added roughly the same amount to the coolant reserve tank.

I expected that once I started the engine, the level in the reserve tank would sink down to the normal level and the new coolant would go to fill up the radiator and pump and stuff. But this didn't happen. Instead the level of the reserve tank remained way too high -- the engine wouldn't take the extra. I let the bike run until it was really hot -- into the red -- hoping the fan would turn on... but it did not.

Not really a successful day. Can anyone shed some light?

 

Im not sure how but when i bought my bike the guy had a switch hooked up to the side of the speedometer that i can turn the fan on and off. I just leave it on the whole time except for cold days. As far as being to full just try to drain everything and give it a good flush. My manuel says it takes 2.5 quarts for the radiator and engine and .37 in the reserve. Hope this helps.

 

OK, the cooling system has a few different and independent parts.

The radiator, radiator cap, cooling fan and thermo-switch, and overflow tank.
The thermosensor, and temperature gauge.
The thermostat and water pump.

The radiator cap does more than just keep the coolant in the bike. It's to regulate the pressure inside the cooling system. When the bike gets hot, it builds up pressure inside the cooling system which raises the boiling point of the coolant. If your radiator cap is not working, your bike would boil over really easily. It's also not located at the top of the radiator by mistake. When the bike is low on coolant, there is an air pocket at the top of the radiator. As the pressure builds up, the air is alowed to escape through a hose that is attached to the overflow tank. This hose is attached at the bottom of the tank. As the engine cools, it draws coolant back into the radiator through this same hose. It can take several heat/cooling cycles in order to bring the coolant level back to full if it's low. The better option would be to open the radiator cap (when it's cool) and fill it back up. Also what CBRfenatic93 said about flushing is also a good idea.

Now, for the cooling fan. The fan has a thermo-switch (the automatic fan switch you replaced) wired to it that, when the radiator gets hot, turns on the fan to cool it off. This is an important distinction. It's not when the engine gets hot, but when the radiator gets hot it turns on the fan.

The thermostat's function is to regulate the operating temperature of the engine. As the engine warms up, the coolant in the engine gets hot too. As this coolant heats up, it causes the thermostat to open. Since the water pump is already pumping, water starts to circulate from the radiator into the engine and back again. It's this circulation that allows the hot coolant in the engine to flow into the radiator. When you first start your engine, you've got cold coolant in you radiator, which cools the engine really effectively. The thermostat closes somewhat so that the engine doesn't cool too much by regulating the flow.

The thermosensor, senses the temperature of the engine and displays it on your gauge.

As the coolant in the radiator finally gets hot enough the thermo-switch turns on the fan to cool it off.

TMI ?? You tell me...

 

Dirt: thank you for the description of the system. I had been wondering whether there was an actual thermostat that allows the coolant to flow.

Today I took the bike out. After 5 miles, I saw that the temp was up to the red -- not a good sign for a 40 degree day. Still, the reserve tank was way too high. And also, the fan never turned on. So it seems that the coolant in the radiator is too low, going by Dirt's description. The radiator was barely warm, while the engine was overheating.

My next step will be as follows. Siphon out the extra coolant from the overflow tank. Then add coolant in the radiator until it is full. Hopefully then I'll get the proper flow through the system.

Does it make sense that the coolant in the reserve tank was never sucked in by the system? Could I possible have a plug, somewhere?

 

In order for the coolant to be drawn back into the system, the bike and coolant has to be heated up, then allowed to cool completely, like overnight. Then heated again up to operating temperature, then allowed to cool off again. Based on your description, the bike is probably so low, that it's not circulating coolant through the system. The radiator is never getting hot enough to turn the fan on, but the coolant (however much there is) in the engine is getting really hot.

I'd definitely take the extra coolant out of the overflow tank and then fill the radiator to the proper level. Then take for a test ride. I think you'll be ok then.

 

Aha, fixed! I siphoned all the coolant out of the reserve tank and filled only between the marks. Then I added fresh coolant to the radiator until it overflowed. Then I ran the engine for about 10 minutes. Once the temp gauge got about halfway up, the fan turned on! So like you said, I think the level in the radiator was actually low enough to not touch the sensor (that's pretty low.) Glad this didn't go on for any longer than it did.

I haven't been out again, but I'm certain that it will be fixed when I do. Thanks guys.

 

Great job man, way to go. It's always a nice feeling when you fix it yourself. Congratulations.