temperature gauge behaviour?

set off out for a ride today in the rain, all waterproofs on except for my overshoes, after about 10 miles i thought i'd stop to put these on and when i did i noticed a heavy stream of water that looked like it was running from the radiator. Not sure if it was a leak or not i decided to forget the overshoes just incase and set off home. While riding home i paid particular attention to the temp gauge and noticed that it was steadily rising up to 92 and then steadily dropping back down to 78. When i got home i left the bike running to get the temperature to rise to see if the fan was kicking in to cool it down again and it wasn't, it was just going up and down on it's own.
I have since checked the coolant level and this is still at the full mark, so am pressuming that it was just the rain water running off the radiator, but is the temperature difference normal or is there likely to be a thermostat issue?

[DJ123]

in the rain it'll be cooling down along with the cooler air hitting it. IIRC the fan doesn't come on until 110 so it has to be really hot before it kicks in. See what it is like on a normal day, not too hot or too cool. should sit slightly less than 90

[Sid Squid]

The water stream you saw was rain kicked up onto the radiator by the front wheel, and is quite normal.

The themostat is not a switch, it takes a certain time to open and close, and when you're riding in cold weather the radiator is being heavily cooled, cool water from the radiator flows through the engine and cools it significantly also cooling the 'stat as it does so, the 'stat starts to close but it takes longer to do so than it does for the engine temperature to fall significantly, when the 'stat closes the engine temperature rises but in the time it takes to fully open the engine temperature has risen significantly and the cycle starts again.
This is why you see the gauge rising and falling. Many water cooled engines will do this if the circumstances are just right, sometimes two identical bikes will act differently - I suspect that some supposedly indentical 'stats just operate a bit quicker than others.

On a cold day the radiator alone may dissapate enough heat to keep the engine cool, thus the fan will not run.

cheers for the info guys, normally the temp stays quite steady and i don't ride in the rain a great deal so was quite surprised when i saw the water running off the rad, and then i probably kept my eye on the gauge more than i should on the way home.