I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: fans come on incorrectly
I've been observing similar behavior for the first time during heat waves this summer. At the ambient temperatures of around 38°C (100 °F) we've been having these past weeks, possibly elevated further when stuck in traffic, or at the lights in a busy street, the fan is able to keep the temperature from rising, but not to drop it to the fan-off threshold. Once I start moving, even at a slow pace, the coolant temperature starts dropping again. I have the feeling that the behavior is not always the same, as sometimes the fan does seem to be able to do its job, but I can't be certain. While moving, temperatures seem to be reasonable.
I'm leaning towards a thermostat that's beginning to stick, not opening fully, at least not all the time. This would explain the erratic bahavior, provided it's not imagined. I also considered the possibility of failing connections at the fan, dropping voltage and hence fan speed, as this seems consistent with the fact that the problem is mostly visible when standing still, with the fan on. I haven't noticed any change in the pitch of the fan noise and the fan still seems capable of blowing lava-hot gusts of air past my legs, but then again, the problem is marginal, so there's no reason to believe that the associated reduction in the fan's performance, would be noticeable. The alternative source of resistance and voltage drop, proposed by BillV escaped me, but is also quite possible.