View Full Version : Auxiliary engine cooling fan - what temp does it kick on?

06-08-2013, 03:55 AM
I'm currently on a road trip with a loaded (within 500lbs of max weight) T1N 2006 1500 and I noticed the fan never kicked on today. The max outside temp registered 123. Using a scan gauge II I could see that I had her up to 225, but no aux fan. Is there a set temp when it should kick on? Is there any way to test it other than run up the temps?

I reached max temp outside of Barstow climbing the 16 mile grade. I quickly hit the truck lane and scooted up at 40mph. I'm trying to not blow her up. She runs strong with 105,000 on the odometer.

06-08-2013, 04:16 AM
This has been discussed in other threads, but my flaky memory says about 205 to 210 F

I also recall it tending to kick in when i slowed down (hence less rammed airflow) after a hill.


06-08-2013, 06:01 AM
My memory says 205F


Aqua Puttana
06-08-2013, 02:47 PM
Are you certain that it didn't kick on? Other than going downhill did you notice any times that the engine temperature dropped and then slowly climbed back up to drop again?

I found my aux electric cooling fan was not turning easily by hand some time ago. I lubed it and freed it up. I was fixin' to check the operation, but using the dash gauge as an indicator I didn't have any overtemp problems even while towing my boat so didn't test it.

Just a couple months ago I was towing my boat back through Pennsylvania. High 80's ambient temperature. I had more passengers and gear than normal because I had another boat's crew on board. On long climbs I noticed a little noise (not a roar as some have described) and then noticed that the engine temperature dropped back a bit. This happened only a few times. The temperature came down fairly quickly each time that I heard the fan come on. It didn't drop like a stone though.

The dash temp gauge is scaled 35F per division. The mark between 180 and 250 is 215F. My fan was kicking on when the temp was a bit above the 215F mark, maybe as high as 225F. :idunno: I don't have an engine performance monitor device. I have operated around and slightly above the 215F area many times while towing and have not noticed the fan coming on.

I don't know what the setting is supposed to be. It is higher than 215F based upon my experience. The air conitioning high side pressure can also turn on the aux fan. That may be why some people see lower engine temperatures with the fan on.

... Is there any way to test it other than run up the temps?
If you pull the engine temperature sensor the loss of that sensor signal should cause the ECM to kick the fan on.


06-08-2013, 02:56 PM
I recall the fan used to have quite a roar, so I should have noticed it especially since I was expecting it to come on and there were no drops in temp without me slowing down and killing the AC. 225 is a bit less than half way through the last white indicator on the dash before getting into the red according to my scan gauge.

Ill track down the sensor and see if it comes on.

06-08-2013, 04:40 PM
Are you talking the engine driven, viscous coupled fan, or the electric aux fans? I have never heard the aux fans. The viscous fan how ever makes a great roar and you can see the temp drop on the scan gauge very quickly.


Aqua Puttana
06-08-2013, 05:15 PM
Are you talking the engine driven, viscous coupled fan, or the electric aux fans? I have never heard the aux fans. The viscous fan how ever makes a great roar and you can see the temp drop on the scan gauge very quickly.

The conditions which I notice my viscous clutch/main fan roar is when we are at normal to slightly high operating temperature and, for one example, coming to a highway stop. I believe that the viscous temperature sensor heats up during that stop time. That locks the clutch and I notice a roar at lower speeds as I pull away. It generally quiets down quite quickly. I haven't noticed a main fan roar during at speed highway conditions. I think that I would recognize it.

The circumstances which I described in my post above were definitely the aux electric cooling fan. vic

06-08-2013, 06:46 PM
Climbing a long grade at high ambient temps, I can clearly hear the engine driven fan fire up and off, and I can see the coolant temp drop accordingly.


Old Crows
06-08-2013, 08:52 PM
Coolant temperature tells you coolant temperature... you need to know the temperature of the air beig drawn through the radiator...Old school testing was to do this: when cold the fan should spin freely. However, when you start the car from cold...the fan should engage until the silicone redistributes and the fan disengages. You should hear it roar and feel a stronger air flow when it's engaged ant that will disappear when it goes to "free wheel" mode. Ok, next test.... Be very careful here!!! You need to block the radiator with cardboard, plastic or styrofoam sheet, or what I've used once, a heavy horse blanket. Insert a pencil type thermometer between the radiator and the shroud so you can read the dial. The objective is to measure the air temp coming off the radiator and before the fan. BEEE VEEERY CAREFUL!! Crank it up! Let her idle ...maybe at a quick idle... Eventually... The thing will get hot enough to cause the viscous fan to engage... You will hear and feel it! Note the thermometer temp! Check the manual for correct operating temperature. Temperature should begin to drop right away. Pull the cover material and it should cool down and the fan will cut off. Easy as pie!

06-09-2013, 03:59 AM
Well, after messing with the sensor and moving the fan a bit this morning the fan kicked on at 200 on the mark and cycled on and off all day. Normally my tinkering breaks things, so cheers to it going right! Thank you gents for your advice and direction.