Engine Overheating - Radiator Fan Problem

One of the most common problem with engine overheating is radiator fan failure. Here you will learn how to solve engine (radiator) overheating problem in a step by step procedure. Find causes and cures for this problem. As we've mentioned in our other engine overheating tutorials, the moment the car starts overheating, pull it to the side and check it out. When the coolant circulation is in order, the next thing to do check is the radiator fan.

Radiator Fun Troubleshooting

The radiator fan is an electric motor that spins the fan which produces an air flow through the radiator. The right way to diagnose this defect is: Turn on the car. Let the engine run to it's normal temperature. Touch both of the hoses that are connected to the radiator. If they are equally hot and the engine is starting to overheat the fan system is faulty.

The tools you'll need for the job are:

  1. set of wrenches that match the job
  2.  multi-purpose screwdriver
  3. electric tester or a multimeter.
  4. isolation tape

Here's what to check:

  1. the electric input/output on the
    • Fan motor
    •  Thermo-switch (you'll recognize it by it's position on the radiator and the wiring on it ).
      radiator fun problem
      Radiator fun
    • The fuse in the main fuse box
    • The radiator fan relay (optional) : you'll find it near the thermo-switch or on the fuse box.
    • The wires themselves incise of a snapped or damaged wire. (In all of these checks use the tester or the multimeter.)
  2. The therm switch - There's no simple way of testing the switch .The most simple and fast way to do it is by cross connecting the two cables on it. If the the thermo - switch is faulty the radiator fan will start to wor Watch your hands. Be sure to keep a safe distance from the fan propeler!!!!
  3. The fan motor - Disconnect the motor from the rest of the installation and test it (one wire on "+" other on"-" on a car battery).

Once you've located the exact malfunction here are the repairs: 

  1. Bad fuse: replace the fuse. If it burns out again there's a short circuit or overload. Don't replace it again, your riskin damage to the installation.
  2. Bad relay: replace the relay with a new one. The replacement is simple. Take it out of it's socket and push the other one in.
  3. Bad wiring: if you find a snapped or damaged cable, reconnect and isolate it with isolation tape
  4. Bad thermo switch: once you've defined that the switch is faulty here's what you do:
    • let the engine cool down completely
    • disconnect the wires from the switch
    • put a container under the switch to catch the coolant that will come out
    • take the proper wrench and loosen the therm switch. Be careful, as you loosen it coolant will start to come out under pressure.
    • once the coolant has stopped flowing, screw on the new switch. Make sure that the seal-plate is on, otherwise there will be a leak. Note: while tightening the switch, be careful, don't over do it because the thread is sensitive.
    • reconnect the wires as they were on the old switch
    • start the engine and once it heats up, make sure that the fan starts at the right temperature.
    • check for possible leaks
    • add additional coolant fluid if you've spilled some during change
  5. Bad fan motor: if you've concluded that the motor is faulty, replace it with a new one.
  • detach the wires that go on the motor
  • detach it from the radiator (most cars have a motor fan holder on the radiator, comes down with the motor)
  •  take the motor out of the holder unscrewing the screws that hold them together
  • put the new motor (with the propeller on it, of course) on the holder
  • put the holder back on the radiator and reconnect the wiresf)
  • start the engine, warm it up to work temperature and check that it works. You can also try it on the working table connecting the "+" and "-" cables to a car battery.