Title says it all. I have been battling a over heating problem for too long. It only over heats when going up hill. Anyways I checked the air filter. Clogged with dirt and crap. So I washed it out and installed it. Went on a canyon drive and no overheating. I'm not too sure. Can a air filter cause overheating?

No. All a clogged air filter will do is 1) reduce maximum engine output somewhat, and 2) reduce fuel mileage slightly due to higher pumping losses ... but both will occur only at or near full throttle. At less than full throttle, a clogged air filter is just another intake restriction that you unconsciously compensate for by opening the throttle a little bit more than usual. Your throttle plate is the biggest intake restriction of them all.

[This message has been edited by Marvin McInnis (edited 09-27-2009).]

The Fan kicks on at 210 degrees so when your going up hill the engine temperature will climb rather quickley.The 84 Fiero held 3 quarts of oil insted of 4,so they ran hotter.Check for water in the oil (milkey brown).A stuck thirmistat will cause your car to run real hot.A bad fan relay will prevent the fan from comeing on, causeing the temperature to cool while driveing, but climp while stopped.Do a coolant pressure test to see if you have a pressure leak.Might be the wrong rad cap.