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Engine thermo fan

Intermittent thermo fan running all the time with cold motor request engine wiring diagram inc relays etc

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We do not have these wiring diagrams. Sorry

Posted on Feb 18, 2012


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Posted on Jan 02, 2017

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SOURCE: Fan blows intermittently. Sometimes works, sometimes doesn't

You need to replace the motor and resistor at the same time. The motor is not turning freely enough and will build up resistance in the wire and this will short out the resistor relay. I sold a lot of resistors working at a Isuzu dealer and if you did not replace the motor, the new resistor had no warranty on it. So if you just replace the resistor relay you will burn it up again.

Posted on Aug 12, 2009

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My car starts an runs but the radiator fan is not coming on and it over heats fast. But the warning lights don't pop up on the dash board

f the engine shows signs of overheating, stop and look to see if the fan is working. With the type operated by the Connect the motor feedterminal to the live terminal onthe battery.

Check a fan motor for faults

Fan motor with the thermo-switch lead disconnected and test lead connected to the battery.Look at the battery, and take off the wiring terminals to the motor or disconnect the plug. Free the wires from clips or other fixings on the fan
A new motor is supplied without a fan, which must be refitted from the old one.The motor and fan normally come off as an assembly, but you may also have to remove the shroud and sometimes the radiator.
Separate the components. Clean the parts that are to be reused, simply by degreasing or even by repainting.
Checking the new motor When you fit a replacement motor, check it by connecting its leads directly to the battery. Be sure to connect the positive (+) and negative (-) leads to the corresponding battery terminals.Take care - the motor will kick as it starts and there will be a large spark when it is connected.
Checking the switch for faults A thermo-switch with push-on connections. The switch is threaded and has a sealing washer which must be renewed.If the fan motor is not at fault, leave the ignition switched on, take the connections off the thermo-switch and briefly touch them together.
If the fan motor now works, the switch is faulty. If it does not, check to see that there is current flowing to the switch by using a circuit tester on the feed wire to the thermoswitch.
Touch the leads together to bypass the switch.If the tester does not light, trace the lead from the thermo-switch back to its power supply; the car handbook may have a wiring diagram
A detailed drawing showing the location of electronic components and devices that are connected together in a circuit.
.If the tester lights, trace the lead from the thermo-switch through to the relay and check the terminals for tightness and cleanliness. Clean and tighten as necessary. Changing a thermo-switchThe thermo-switch is normally located in the radiator bottom tank, in the How to flush an engine radiator) until the coolant is below the level at which it is fitted. Catch the coolant in a clean container if you plan to reuse it. If a rubber cover is fitted over the back of the switch, ease it off, then disconnect the electrical connections.
The switch can now be unscrewed from its mounting point with an appropriate spanner. It may, however, be very tight, so take care not to distort the surrounding metal if it is fitted in the radiator bottom tank. Always fit a new sealing washer.
Checking the relay for faultsWith the ignition switched on, short-circuit the thermo-switch by putting a screwdriver across its two terminals; do not disconnect the leads. You may be able to hear a click from the relay as it operates. Test for current with a test lamp or circuit tester at the 'live' lead to the relay - again with the ignition switched on.
If there is current here but, when the thermo-switch is bypassed, none at the terminal for the fan-motor lead, the relay is faulty and must be replaced.
Checking the T-piece On the Datsun Cherry the thermoswitch and connections are in a T-piece on the bottom radiator hose, so look there if the switch is not on the radiator.

Sep 30, 2016 | Cars & Trucks

1 Answer

Thermo fans running on after engine is cool

Faulty switch, relay or wiring on earlier models. Later models probably have the cooling fans operated via relay(s) by the engine management system.

I suggest you check on a wiring diagram how yours are operated if checking the relays, switches or sensors don't bear fruit.

Aug 01, 2016 | 1999 Jeep Grand Cherokee

1 Answer


you changed the thermo switch and relays and it didnt fix it
did you test the fan motor itself

the fuse box cover should have a fuse layout diagram
engine cooling fan

look for a 30 amp fuse

they usually near the fan relays

is the air con cooling fan working with air con on
and engine running


Jul 15, 2016 | Toyota Cars & Trucks

1 Answer

Left hand driver side fan will not switch on and radiator boils over slightly. Air Con works great. Which relay in the fuse box should I check?

The fan circuit consists of a 30 amp fusible link and a relay in the engine compartment fuse/relay block and the thermo-switch on the little coolant manifold near the driver side end of the engine. The relay is the one on the far right side with the fusible link just below it. I would question the thermo-switch first. To test the circuit you can short the wire that goes to the thermo-switch to ground, with ignition switch on, and the fan should run. It not then check and relay. See the attached diagram for thermo-switch location. Do not take the part numbers on the diagram for gospel. I drew this up several years ago. I do not have my Camry so I cannot totally verify the above. I tried to post an answer several days ago but was not logged in at the time and they would not post it! 310bec86-8097-4e0b-9e5c-c6e4a17e69d4.jpg

Aug 03, 2014 | 1988 Toyota Camry

1 Answer

1987 honda civic

Disconnect the electrical at the top. Sometimes you can get the fan out and then the shroud-due to limited space. They would both come out from the top.
We mechanics will tell you to test the fan motor with jumper wires from the battery before you decide to pull it off. On most cars, the computer turns the fan on through a cooling fan relay. On your '87, it is possible that a thermal switch on the radiator may turn the fan relay on at a set temperature. One would have to see a wiring diagram.

Just looked at a diagram: If your car is fuel injected, check fuse #13, a 15 amp blue fuse. And same if carbureted, fuse #13-this fuse is for the relay and the fan motor. If carbureted, also check fuse #20-a 20amp fuse.
There are no computer controls for the fan on an '87. there is a thermo switch-at a set temperature, the switch will close-completing the ground path for the fan motor. There is also a radiator fan timer switch, tied in with the thermo switch and the air temperature sensor.
Sound complicated? Well, it is, even with no computer controls. If the fan motor is good, check or replace the thermo switch. Be sure and check those fuses, also. If no help, a tech will probably have to diagnose it.

Jan 29, 2014 | 1987 Honda Civic

1 Answer

My car is overhit,the thermo in new,the bleed is than but stil overhit


Jul 29, 2010 | 1999 Oldsmobile Alero

3 Answers

Radiator fan not stopping even when i turn off the car and remove the keys. this is leading to battery drain

Radiator fan is supposed to start working after the temp reaches a certain limit. And it is supposed to run til the temp reaches a certain lower limit. So when you switch off the engine and walk off the fans must be running to cool the water to that lower limit. Unless you seen that it runs well past that and does not stop at all. Does it start running when you start the engine? And runs throughout the time the car is running, which it should not. The relay seems to be out. It is this relay that controls the running of the fan. or the temp gauge. If the temp gauge is giving wrong temp then the relay has to keep working. Please check both, the relay and before that the temp gauge.

Dec 14, 2009 | 2000 Volkswagen Beetle

2 Answers

Cooling fans on radiator will not run. Voltage in plug at block thermostat is 5.4.this therm provides an earth switch. Bypassed the thermo to earth and fan relay engages momentarily only. Relay is ok....

The fan control thermo switch should be either "off" or "on".
Voltage should measure either +12 or 0V, depending on coolant temperature.
Replacing it should fix your problem.

Jun 20, 2009 | 2000 Daewoo Nubira

1 Answer

Fan motors

Check that the fans are still working .Check that the thermo switch is working.Check that you have power to the thermo switch. and if not check relay/supply of power.Unsure with your model but the thermo switches are usualy screwed into the radiator but could be mounted on the engine.You can check your fans by running a piece of wire from the positive terminal of the battery to the positive side/wire of the fans.As long as the fans are earthed as well they should work and if not then the fans will need to be replaced.

Oct 10, 2008 | 1990 Nissan Maxima

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