Hi

Got my 05 Pro out a couple of weeks ago and after 5-10 minutes (it was a hot day) the fan came on. However, it refused to cut back out again and stayed on. Rode for another twenty minutes with the fan on constantly then put the bike away.

Checked coolant level when I got home, and all was well.

The next day I got the bike out, and immediately upon starting it the fan came on and stayed on again.

This situation has remained ever since, with the fan coming on as soon as bike starts. I have checked electrical connections on thermostat are solid and WD40'd wiring etc.

Can anyone help with suggestions as to what I should check and how, it would be much appreciated as I've not had much mechanical experience with watercooled bikes.

Thanks for any help at all.

Hi

Got my 05 Pro out a couple of weeks ago and after 5-10 minutes (it was a hot day) the fan came on. However, it refused to cut back out again and stayed on. Rode for another twenty minutes with the fan on constantly then put the bike away.

Checked coolant level when I got home, and all was well.

The next day I got the bike out, and immediately upon starting it the fan came on and stayed on again.

This situation has remained ever since, with the fan coming on as soon as bike starts. I have checked electrical connections on thermostat are solid and WD40'd wiring etc.

Can anyone help with suggestions as to what I should check and how, it would be much appreciated as I've not had much mechanical experience with watercooled bikes.

Thanks for any help at all.

You should expect the fan to come on fairly quickly on a hot day and the hotter it is, the more the fan will come on. At the low speeds we operate our bikes, the fan is necessary to draw air through the radiator to regulate heat in the engine.

If the fan comes on at very first start, there is a good possibility that the thermocouple ("thermostat") switch is stuck and probably should be replaced. You can check the switch with a pan of water on the stove, a thermometer and a continuity meter if you want to see what temperature the switch makes contact. Keep the switch off the bottom of the pan (otherwise the switch temp, touching the bottom, will be hotter than the ambient water temp reading on the thermometer) and gradually allow the temperature to rise until the meter indicates a closed circuit.

Jon

Good advice given above. If I could just add one thing. Before doing all that pull one or both wires off the stat whilst the bike is running. If the fan stops then go ahead and test the stat as above. However, if the fan still runs with the open circuit then you have a wiring fault elsewhere.

Hi again.

Thanks for the prompt, clear, and excellent advice.

Posted before I went and had a good look at the bike and yes, once the wires were taken off thermostat the fan went off.

Didn't have time to check thermo switch but replaced with a new one from local dealer and hey presto, all seems fine again with no fan on anymore.

Will test old switch this week just to confirm that it was duff - only worry now is why it went - dealer suggested rectifier may be problem if this one goes too (they have seen this happen a few times).

Thanks again for all your help.

Cheers.

Glad you got it sorted. I'm not sure quite how the switch works, I'm guessing some sort of bi-metal strip. I have had the odd one fail myself.

I remember one failing the day before a national trial. I bought a car thermostatic switch from the local factors. It looked a similar size but thread was bigger so I turned it down in the lathe and cut a new thread. I stuck it in and added an overide switch as precaution. Bike ran faultless all day. I did order the correct switch the next week and kept the other as back up. I do remember there was a huge price difference between the two though!

Good advice given above....

I agree! JSE is a valuable resource on this forum. Keep up the great work, JSE!

I agree! JSE is a valuable resource on this forum. Keep up the great work, JSE!

Awwww, thanks. I find this forum quite valuable and I'm sure that others (like PeterB, for example, who has given me a lot of good pointers) will agree that being able to tap into the collective knowledge of riders from all over the world at the click of a computer key a really neat thing!

Jon