I have a 2000 Kia Sportage 4x4. The tempeture gauge flucuates wildly while I'm driving. When I drive around town the tempeture gauge will occasionally go pass the halfway mark but always drops down to slightly below halfway when idling (like at a light) but the instant I put it in gear (5 speed manual) and give it gas the gauge will climb again. Today I went on the highway and within 4 minutes the tempeture gauge was slightly over 3/4 way to the top so I pulled off the road. As soon as my speed dropped below 45 MPH the gauge went back to 1/2. As long as I stay under 45 MPH the guage stays in a reasonable range but when I reach highway speeds the tempeture increases drastically within seconds. I have replaced the thermostat with a factory model last weekend hoping that would fix the problem but no such luck so this morning I replaced the radiator fluid (because I'm not a mechanic & it was fairly cheap to do myself) and the spark plugs and wires (because I was due) but I still have the same problem. Any suggestions since Kia warranty shop tells me the problem I describe isn't "logical". Even though they can duplicate it they can't explain it or repair it and refuse to acknowledge it in writing.