What Can Make an Engine Overheat?

Overheating is caused by anything that leads to a loss of coolant, prevents the cooling system from getting rid of heat, or causes excess heat in the engine itself:

  • Coolant leaks (water pump, radiator, heater core, hoses, freeze plugs, head gasket, engine internal).
  • Weak radiator cap (does not hold rated pressure and allows coolant to boil over). Pressure test the cap to check it out.
  • Cooling system clogged (deposits built up in radiator or in the engine due to maintenance neglect or use of hard water). Use a cleaner, then reverse flush system to clean it out. A badly clogged radiator may need to be rodded out or replaced.
  • Thermostat stuck shut (replace).
  • Inoperative electric cooling fan (check fan motor, relay and temperature switch for correct operation).
  • Bad fan clutch (replace if slipping, leaking or loose).
  • Missing fan shroud (reduces cooling efficiency of fan).
  • Slipping fan belt (tighten or replace).
  • Too low or too high a concentration of antifreeze (should be 50/50 for best cooling).
  • Bad water pump (impeller eroded or loose - replace pump).
  • Collapsed radiator hose (check lower hose).
  • Debris in the radiator (remove bugs & dirt).
  • Late ignition timing (reset to specs).
  • Restricted exhaust system (check intake vacuum readings and inspect converter, muffler & pipes).
  • Radiator and/or fan undersized for application (increase cooling power by installing larger radiator and/or auxiliary cooling fan).
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