here's the scenario. first i was driving to the beach on a rather hot day and i had the A/C on. it was the first really hot day we've had and that i have driven the car in (got it in NOV.) i noticed that the temp gauge was above normal (bout halfway between normal and pinned) so i shut off the a/c and it went to normal

today i was running the car really hard at a local track and it did the same thing. (no a/c) i would have to let my car rest for a short bit to cool down. then it was ok.

My coolant is as green as grass and my fan works. the only thing i can think of is that the secondary fan isnt kicking on with the a/c, but would that explain why it is overheating when i run it hard??

Justin

 

If it's overheating at highway speeds, then it's probably your radiator (clogged), maybe your thermostat.

 

it cools fine as long as i am not running it hard and there is no a/c on

Justin

 

Still could be the radiator. The A/C dumps all its heat straight through the radiator, which reduces it's efficiency, but it is sized from the factory to cope with this.
The auxiliary electric fan is really only there to help the A/C at low speeds and when stopped (it's just simpler to run it whenever it's on). Once you're up and running it shouldn't matter if it's going or not, but it's easy to check. With the ignition on, turn on your A/C (and the interior fan) and see if it's running.
If your radiator is partially blocked it may have enough capacity to cool the engine when there's not too much load on it, but not when the going gets a bit tougher. Same thing if the thermostat is not opening fully. Check the thermostat as per the FSM. If you need to replace it only use a Mazda one.