Hello. I just bought my mom's 98 civic DX. It has had a problem where it drives around fine in city type driving. However, if you drive more than 100 miles, it will overheat. She has had the radiator replaced as well as the thermostat. Also, I sat the car at idle yesterday for 15 minutes and the temp. was low, but the fan never kicked on. At one point, my mom overfilled the oil and it spilled into the coolant. The coolant res. is black coated, but the coolant is clean and green. The car really runs perfect around town. I just need to drive 6 hours next week and would like to resolve this if possible. Any suggestions? I cant help but think the thermostat was installed wrong and there is a bubble in the system, or a headgasket issue?