In 90% of the cases, coolant leaks are the culprits that cause overheating.  Please check out our coolant leak page here:
FC3S Pro - Problems #1, Engine, Coolant Leaks

If possible, get an aftermarket water temp gauge to confirm the engine is overheating.  Relying on the stock water temp gauge is not a real good indicator of accurate water temperatures.

Since the cooling system is not very complex, we can tackle other possibilities one component at a time.

Thermostat - FC3S Pro - Problems #2, Engine, Thermostat

Radiator cap - FC3S Pro - Problems #2, Engine, Radiator Caps

Water pump - FC3S Pro - Problems #2, Engine, Water Pump

Radiator - FC3S Pro - Problems #2, Engine, Radiator

Water pump housing - corrosion can degrade the water pump housing enough to affect the water pump efficiency.  Inspect the water pump housing surface directly across from the water pump impellers.  This surface should be machined smooth without any pitting or grooving.
Replace water pump housing

Stock viscous fan - FC3S Pro - Problems #2, Engine, Stock Viscous Fan

Water temp sensor - although rare, the water temp sensor can go bad.  The Mazda FSM has the temperature versus resistance table to check the sensor.
Replace water temp sensor

Bad engine - if all else fails, there's a possibility of a broken water jacket or a bad water jacket o-ring.  If coolant is being lost, and there is no obvious leak anywhere, check the exhaust.  If coolant is being spit into the exhaust or you smell the sweet smell of burning coolant, it's pretty much confirmed the engine is bad.  Check to spark plugs for signs of burning coolant - the tips should be very clean and / or white, frosted.

Questions?  Comments?  Send mail to:  reted@fc3spro.com

08/27/2004