Radiator fan mystery, everything checked fine.

I have been living with this problems for a number of years. My work around is to turn on A/C to keep the fans running.

Problem: My radiator fan will not turn on in response to rising engine temperature, even up to 80% on temp gauge.

I have pulled the radiator fan switch (at the lower radiator, passenger side) and tested it with boiling water per FSM. The switch works fine. While the switch is out, I put water into the radiator filler neck and surely see water coming out from the radiator fan switch opening so there is no blockage. When I jumped the two pins of the radiator fan switch connector, the radiator fan will turn on. According to the schematic diagram, as long as the radiator fan switch closes in response to rising in coolant temp, it will energize the radiator fan relay and the fan will turn on (and turn off when temp drops). I am scratching my head as this is very simple and all components are checked and good.

Any ideas ?

Dumb question does the timer box under the passenger seat have anything to do with the circuit?

I was thinking about the if the timer box will interfere with the operation. But after reading the schematic, it will not. Its job is to give 15 more minutes to run the radiator fan after engine shut off if the coolant sensor B at the thermostat housing closes due to a higher coolant temp.

I have another thread going with regards to this. I have checked all fuses, replaced all Temp sensors on radiator & thermostat housing, burped rad fluid to make sure no air bubbles, replaced electrical plug from key switch to fuse box. A/C and Radiator fans do not come on. Jumped both fans at radiator, they both work fine. I have voltage @ all Temp sensors.

I guess next step is to check current from Fuse box to Timer unit & fan controller. Yellow/Black wires I believe.

Have you verified coolant temp at the fan switch? It could be the gauge weirding out.

Snooz, are you talking about the lower radiator passenger side, where the radiator fan thermo switch located ? Yes, I took that switch out and put in boiling water just like the FSM and checked the switch. Also, while the switch was out, I pour water into the radiator at the top of the radiator filler neck and water came out from the thermo switch hole so I know the radiator is not blocked. I'm going back to check all fuses and get the passenger seat out to check the timer box.....

I pulled the passenger seat off, checked the timer and its clean, no water damage, no oxidation at the connector and pins. Checked all the fuses under the hood and all good. I sprayed the connector and the pins with electrical contact cleaner anyway.

I don't think I would ever able to figure it out unless I jump a signal wire at the coolant temp switch at the radiator to see if it actually closes when temp reach threshold...I have thought about this using a little 12v lamp or an LED from the switch wired into the cabin to observe switch function in real driving condition....

No. Are you sure the coolant temp is getting high enough to trip the switch? Check the rad temp with an infrared thermometer.

I see. I dont have an infra red thermometer. I can only rely on the dash temp gauge and assuming it is accurate (it may not).

https://www.harborfreight.com/catalo...ed+thermometer

Quote:

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Originally Posted by Dr_Snooz

https://www.harborfreight.com/catalo...ed+thermometer

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I have one like this, but the range is for taking human body temp....

I will get one when I get that HF coupon in the mail.