Cooling question?

[Kev659]

The question i have is reguarding the fan circuit. The previous owner of the car cut out the fan control sensor from the circuit and spliced in a fan on off switch in the cabin. I reciently removed that setup and bought a new control sensor and set it up as it was shown in the wireing diagrams. Now when i run the car the fan does not turn on. With the other setup i could flip the switch and turn the fan on so i know the fan works. I ohmed out all my cables so i know i have good contact. I also checked the voltages and the positive side of the fan is recieveing 12 volts. now when i connect in the fan control sensor nothing happens. The engine will heat up and the fan will not come on. At what temp should that fan come on? Does anyone have any ideas about why that would not turn on when the temp came up? I reciently found that my radiator cap is back would that cause the problem? I am drawing a troubleshooting blank here help or suggestions welcomed.

[kmead]

Your fan won't come on until it reaches the preset temp of the sensor. Do you know the temp rating of the sensor you installed?

My 124 fan doesn't start until the engine has been running nearly 20 minutes from a cold start. The Fiat thermostat for the engine tries to keep the engine at about 190°, it does this by regulating the amount of cooled coolant that is circulated. The radiator fan switch will come on when coolant exiting the radiator exceeds the set temp which may be as much as 220°, generally with the car moving there is usually more than enough air going through the radiator to keep the fan from coming on.

If you have an infra red thermometer you can check to see what the temp of the radiator is and verify the start temp for the radiator fan.

If the fan will run when you jumper the wires together then you know the fan and the related relay and wiring works. If you let the car sit idling/revving until the coolant gauge indicates being in the 210°+ range and the fan comes on, you are also likely fine (presuming that is the set temp for the switch). If it just never comes on then you may need a new switch.

It isn't intended to run all the time so if the car isn't overheating, its likely working properly in use. If it won't turn on despite the car showing obvious signs of overheating (the radiator cap is releasing significant coolant to the overflow bottle and the gauge is in the red) then you clearly have a problem.

You can test the switch by suspending the end of it in hot water that is in excess of the set temp of the switch using a continuity tester, but you need to remove if from the car. At that point I would just replace it with a new one.

[So Cal Mark]

air trapped in the cooling system will prevent the thermostat from opening, thus keeping the bottom of the radiator too cool for the switch to close. Is the radiator getting hot down near the fan switch?

[Kev659]

i put a brand new switch in due to the fact i was uncertain if the old one was good. The bottom of the radiator is getting hot i may just not be waiting long enought for the temp to raise to the point of it turnning the circuit on. What does the temp guage usually ready for normal operation? I will bleed the system and make sure there is no air in it.

[kmead]

Around 210°