The difference between AutoZone and OEM as summed up through thermostats.

After blowing the headgaskets and having the car overheat(not sure which happened first) the AutoZone thermostat was supposed to lock itself open under the high temps. It did not, furthermore it looks nothing like the beefy original design.

The autozone unit has a Much larger bypass(allowing more coolant to flow around the motor instead of the radiator) and a smaller range to open itself to the radiator. While the oem unit is minimal bypass range and allows for itself to open quite a bit allowing exceptional flow to the radiator.

Part of me thinks the AutoZone thermostat had the car running hot in the first place. The waterpump was less than 2 years old, the radiator a brand new supra aluminum unit.

They cost about the same too.