Temp guage issue


This is very strange. I just had the oil changed on my bike at the dealer. I picked it up and as I was riding down the road the temp guage went from just under the center mark to totally cold. I rode down to a gas station pulled over and turned off the bike to check it out. when I switched off the bike the guage jumped to hot then to center then to hot then stayed at hot. this is all with the key removed and everything switched off. Now when I start up it goes back down to center and seems fine but when turning everything back off it shows hot again. I now don't trust the temp guage at all. any clue to what is going on with it

thanks for any help
Hmmphrf. My guage goes to hot when I turn the key on - does your fan come on at all? Even running it at a stand still?
yes it will come on . I noticed it only came on when it was slightly above the center mark. But when it is in the hot/high zone on the guage it was not coming on. I would notice when the needle jumped around the red light would flicker then go off even when the guage showed hot. The bike is not overheating atleast it hasn't yet. the overflow tank has been fine so far.this just started today on my morning ride. it was going all over the place then stop then alittle later change again. also when you first turn the switches on normally all the needles go from low to high then settle to the actual reading . the temp guage does not. sometimes it does nothing sometimes it will go hot then center then go hot and stay there. what controls the needle movement?could there be a bad ground or something like that ?
thanks for the reply
What seems odd is that it started after an oil change? Nothing would have been done that would affect your temperature reading... was anything else done to the bike? Have you modded your gauges? The only signal to the temp gauge is in the main harness... any other gauge problems?
it is a 2005.
I do have illumiglo guages but they have been on for months and no problems. the guages are tied to the ignition switch and ground. all the other guages are working fine. it is just the temp acting up.
well I am taking it back to the dealership. let them take a look. I rode a little more this time when stating up it went directly to hot in less than a second after it had been sitting for 2-3 hours and stayed there. I get no red temp light on and the fan is not coming on . I checked the fan and it will work if connecting directly to power so the fan is ok. looks like maybe a sensor??
I just don't understand why the problem would have started with an oil change. Have you talked with the dealership to see if there is anything they know about it?
I spoke to them Saturday . They said just bring it back in.

So i just don't don't know. Today as soon as I start up it imidiately shows hot on the guage and will never fall below the 1/2 way point line.
I take it in tuesday to the dealership to see what is going on.
Bad news is it is 2 months out on warranty. hope it is not something too serious