99 cavalier cooling problems

i have a 99 cavalier 2.2 automatic trans. ive had it now for about 2 months now. when im going speed limit 100 kms/hour. the temp gauge sits at about the quarter mark, and it doesnt throw terribly warm heat, if i speed up to 110 or faster it goes in between quarter and half and throws lots of heat. i put a cardboard in front of the radiator now because it is very cold here (-30) i had a 97 sunfire previously and my gauge was always at half, when i slow down in town with the cavalier the gauge goes closer to half but when i go on the highway again it goes down. i am puzzled, my sister has the identical car and her gauge stays between quarter and half and her car heats awesome and has no cardboard in front. yesterday morning i noticed a little bit of anti-freeze in the snow under the front passenger side of my car, almost righr under my bumper, im not sure what is leaking, ill look at it on the weekend, could it be that i have some kind of leak and thus air in the system thats why the gauge is up and down?... any help would be great..:confused:

Check the level of the anti-freeze first and if that is good then have a pressure check done on the system. If there is a leak it can be letting air into the system by a weather cracked hose or an early sign of a Head Gasket leak.

well i got the car checked out and it turns out that its the head gasket..... i think that GM should pay for all these head gasket rebuilds ........grrrrrrrrrrrrrrrrrrrr..