The cooling system importance cannot be stressed enough.  The cooling system relies on pressure to work effectively.  Even minute leaks can compromise the cooling ability of the cooling system.  Thus, tracking down and sealing any breaches in the cooling system is the key to a properly working cooling system.  Hopefully, this page will help you track down and fix all the possible leaks that can happen in your FC3S cooling system.

Pic: Leak prone area: Description / Fix:
  Radiator cap Rubber seals under the cap(s) can leak.
  • Inspect the rubber seal to make sure it's in good shape and still soft.
  • Replace with new unit, preferably Mazda OEM
    		•
      Coolant filler neck Plastic unit on Zenki FC3S are prone to cracking.
  • Replace with new unit.
  • Alternate option is to use an cast aluminum FD3S unit.
    		•
      Thermostat cover
      Zenki FC3S    		 Unit can leak at flanges for coolant filler neck and to water pump housing.
  • Remove original and reseal with silicone RTV if necessary.


    • Unit can leak at upper radiator hose fitting.
  • See "Upper Radiator Hose" section below.
    		•
      Thermostat cover
      Kouki FC3S    		 Unit is prone to cracking.
  • Replace with new unit, preferably Mazda OEM.


    • Unit can leak at water pump housing flange and upper radiator hose fitting.
  • See "Upper Radiator Hose" section below.
    		•
      Radiator hose
      Upper    		 Ends prone to leaking.
  • Replace hose clamps.
  • If necessary, replace hose.
    		•
      Radiator hose
      Lower    		 Ends prone to leaking.
  • Replace hose clamps.
  • If necessary, replace hose.
    		•
      Heater hose,
      Lower radiator    		 Ends prone to leaking.
  • Replace hose clamps.
  • If necessary, replace hose.
    		•
      Radiator Plastic endtanks can crack or leak at crimp seams.
  • Replace radiator.
    		•
      LOW COOLANT sensor
      (top of radiator)    		 Rubber o-ring can fail.
  • Replace o-ring or use thread sealant.
  • Replace sensor if necessary.
    		•
      Water pump Unit can leak at flange to water pump housing.
  • Reseal with new gasket and / or silicone RTV.


    • Internal seal failure - check weep hole under front "snout".
  • Replace water pump.
    		•
      Water pump housing Unit can leak at mating surface to water pump.
  • Reseal with new gasket and / or silicone RTV.


    • Unit can leak at mating surface to engine.
  • Reseal with new gasket and / or silicone RTV.
  • Don't forget washer shims on Zenki FC3S.


    • Unit can leak at mating surface to thermostat cover.
  • Reseal with new gasket and / or silicone RTV.
    		•




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

    06/23/2004