My buddy has a 98 gsr. The problem is that when he drives normal, the temp guage stays at normal temp. As soon as he stop at a red light or in traffic, it starts to raise up a little. It doesnt overheat, it just goes up to the half way point then immediately makes its way down to normal temp. This doent happen everytime, only sometimes. He noticed the coolant in the resevoir went from max level to min level but figured that was because he just drained and refilled the coolant and maybe didnt put enough in, so it just took what it needed. Filled that back to max level to see if it does it again. Checked oil with the dipstick and there is no sign of coolant in there. Upper hose is full and hot after driving so my thermostat is operating properly. Any info will help! Thanks!

 

Change the coolant, its dirty.

 

Same thing happened on my old teg, coolent flush

 

Run a coolant flush. Also check your radiator for signs of cracking. I had a small crack on my top end tank on the radiator for awhile. Now that it's hot outside, the car began to overheat while sitting at a light due to the loss of coolant pressure, etc. I finally just broke down and bought a performance radiator for $139 with metal end tanks.