Coolant, Thermostats and Fan Operation Temps

Trunk Monkey

Staff member
Sep 12, 2023
Charlotte, NC
Vehicle Details
'95 Thunderbird with '18 TF 5.3L - SVO Engine
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NORMAL Engine Operating Temp Range: Normal temperatures are from 200°F to 210°F, with excursions to 220°F.

  • Water boils at 212°F @ Sea level ( 14.7 PSIA / 0 PSIG )
  • 50/50 Solution of Coolant / Water boils at 226°F
  • 50/50 Coolant / Water boils at 267°F at 16 PSIG (The OEM Pressure Relief Cap on the 4.6L and 3.8L Engines)
Note: A thermostat's temperature rating is the *Start opening temperature.

  • 3.8L Thermostat starts to open at 193-200°F, Fully open at 221°F
  • 4.6L Thermostat starts to open at 192-199°F, Fully open at 219°F
Factory Thermostats are rated at 195°
Commonly recommended/preferred replacement T-stat temp. is 180°

**Keep in mind that when replacing your T-stat with a lower temp rated T-stat you would need to adjust the fan turn on temp with a tune to see the full benefit.

As discussed below, the 94-97 MN12's have an electric fan which at stock setting, just like the stock T-stat, turns on at 222°. So, if you've changed from the stock 195° T-stat to a 180° T-stat, unless you've adjusted the tune for a lower fan turn on temperature, when you're pumping coolant through the radiator between 180° and 222° you're just circulating hot coolant because the fan is not running.

Radiator Electric Fan Operation:
  • Low speed fan operation starts at 222°F and stop at 214°F; OR when the A/C is on ( and below 48 MPH ). Over 48 MPH it reverts back to normal operation; i.e.: Fan will not kick on until 222°F.
  • High speed fan operation starts when the Low speed fan is on when coolant temperature reaches 228°F and stops at 220°F.
  • In regards to A/C Operation, the Low speed fan will run continuously - except when the vehicle speed is over 45 mph and the coolant temperature is below 220F, it will turn off.

    The air flow / pressure in front of the vehicle may be reduced in certain conditions such as drafting behind a semi-truck or driving with a tail wind.
By: dDub

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