Cooling question
 

Had a lovely ride over to Exmoor the other night (just after midnight, the roads were deserted and it was cool... bliss) but noticed something that I am not sure is right or not.

The temp gauge on the console was fluctuating up and down, even though speed and road were constant and level. Once warmed up it would settle at about 83 degrees Celcius at the lowest and slowly rise up to about 95 degrees Celcius before dropping down.

It did this fairly constantly as a five minute cycle and there were no issues with running. This was a constant speed on a major road with no major hills and we were not pushing it hard, despite being two up.

The Full power ECU was back in it for the trip and the Bike is an S K3. The outside temp was low enough to need a warm jacket at speed, but not much else.

I checked the coolant level today and it was full to the max line and bright green. :cool:

I have been through the Haynes Manual and there is nothing in there that says that this is abnormal or normal. Carol is perplexed, but does not imagine it is anything serious and we have been discussing it this evening. :makelurve:

What are the considered opinions of your good selves on this? :D

Re: Cooling question
 

thermostat opening and closing, fan switching on and off nothing to worry about

Re: Cooling question
 

Sounds like thermostat cycling, though it usually does it rather more frequently like 30sec or something.

Basically the 'stat is at the outlet from the engine, before the rad, so when it heats up the 'stat opens, pushes slightly cooler coolant in the rad through the engine which lowers the temp at the sensor and tends to cause the 'stat to close down a little again, which restricts the flow to the rad and the engine heats up a bit, and so on.

You might want to double check that the rad is actually full of coolant, not just the make-up bottle.

Engines are developed so that the cycling is minimised usually, but bike systems tend to be somewhat crude in many respects and under certain circumstances considerable temperature cycling is not surprising.

A lot of modern cars use thermostats at the inlet to the coolant pump rather than outlet from the engine, and they blend rad return coolant with the re-circulated engine coolant, which can make the system inherently more stable (you don't need to wait for the whole rad contents to circulate before noticing a change in temp). Also "smart" 'stats are more common, which use electronickery rather than simple wax capsules, so can be controlled.