Thermostat/radiator temps

I have a suspicion of a partially stuck open thermostat.

So, tell me chaps; from cold startup does your right radiator upper half get warm before the thermo opens? Up to 45C it's cold, gets a bit lukewarm at around 55C and at about 63C it's 'hot' to the touch. The thermo opens properly at 80C because the left rad suddenly gets hot and temp drops a couple of degrees then comes back up a few times. To my mind it shouldn't get hot at all till the thermo opens?

She sits at 78C within a mile or so of riding at 40-50mph. I noticed this morning that once I hit the motorway doing 80mph the temp dropped to 75C and came back up once speed dropped.

Fan kicks in normally at 106C and turns off at 96C or so.

My mpg figures are quite low but for the 22 mile daily round trip journey she does including 50% town crawling aren't entirely surprising. In the warmer weather a few months ago mpg figures were quite respectable in the high 30's (UK MPG not US)

I see plenty of anecdotal evidence along the lines of 'mine sits at 78 normal riding'. That's not really what I'm pertaining to, it's mainly the cold startup right rad temps.

Your thermostat appears to operating normally. The R/H radiator will see the warm up you are describing due to the small bleed hole in the thermostat, this allows a small amount of flow to the R/H Radiator first. Your operating temp of approximately 78C is normal also on a cold day it can drop a couple of degrees. From memory your thermatic fan turn on and off temps are normal.

Cheers.

Grum

Sounds right to me. Grum explained the results of the bleed hole perfectly and the momentaneous drop in temp at around 80°C is indicative and characteristic of correct thermostat opening.