Topic: Electric fan problems and a question about temp the sensor

[Baller]

My pickup came with a Flex-a-lite fan with a temp probe that's stuck through the rad, at the top, close to the inlet. Fan worked fine a while ago. Would come on only for a second then go off. Never had any overheating issues. Recently, I noticed it was getting a little warm and the fan didn't kick on. Tested a few more times and it's definitely not working as it should. I still have to dig into it but, the probe through the radiator just seems phony. I was also wondering about the placement of the sensor. I know we're instructed, by people that know a lot more about these things than I do, to place the sensor as close to the rad inlet as possible. I'm wondering why we don't place it at or after the outlet of the rad. Here's my thinking. Putting the sensor at the inlet negates any passive cooling the rad does. While driving on a cold day, engine temp could rise, open the thermostat and let fluid through the rad. At the inlet, the fluid will be hot, trip the sensor and turn on the fan before the fluid has a chance to flow through the rad. The fan may never need to be turned on if you're driving through cold air. Why not put the temp sensor at the outlet and if the amount of cooling from the natural flow of air is insufficient, then the fan would be turned on? It seems like you'd want to know what the rad is doing by itself before deciding if you want to get more air moving. Isn't the less you have to turn on the fan, the better?  Maybe I'm thinking abou this entirely wrong.  Let me know.  Thanks.

[sirdeuce]

Yes, the less the fan cycles, without causing an overtemp event, the better. I've not liked to use the sensor that goes through the radiator. If the sensor is open to airflow it's open to weather and dirt. Another thing that can affect an open sensor is the airflow created when the fan comes on. (not sure if that sheds any light here.)
Best sensor location is in the coolant flow coming OUT of the ENGINE, where it's hottest. I've used "adapters" that are installed in the upper radiator hose that have tapped bosses for the sensor that work well enough and I've seen people drill and tap the manifold for a sensor. Some manifolds have extra bungs for sensors. The inline hose adapter requires cutting the hose and using two clamps. Not my favorite as it creates extra possible coolant leaks.
Next best location is on METAL coolant containment. Some sensors are "contact" sensors that are stuck to coolant passages. Don't affix these to the rubber hose or the plasic radiator tank. Don't put these on the radiator cooling fins. Do use heat conductive grease between the sensor and the heat source and insulate the sensor from air contact. Don't use plastic zip ties, they don't last. Use stainless safety wire or hose clamps. I've seen people use JB weld as well, but I don't have the experience with that.



I'd suggest a Davies-Craig fan controller, best I've found yet.

If you want to go a step further look into electric pumps as well. Electric pumps use less power than the belt driven pump and eliminate the thermostat. Also allows the use of an underdrive crank pulley.

[liveoak]

these are the best fan controllers out there (their website could use some work though)
http://www.dccontrol.com/
http://www.dccontrol.com/constant_temperature_controllers.htm
http://www.dccontrol.com/FK45.pdf
they provide variable speed control of the fan, not just on and off. they also come with a temp sensor and connection for ac compressor input and you can adjust the temperature trigger range.

 If you are going to rely on an electric fan for primary cooling, you have to have a good controller. The relay kit the flex a lite comes with is junk.

[Gnarly4X]

Electric fans use less "power"... typically 3 to 5 HP.

However, the fan motor will pull 15 to 25 amps!!  That will add extra stress on an alternator and battery. 

It takes a little HP (1 to 2) to spin and alternator that is charging at 20 amps. 

In my 1985 22R, turning on the headlights at idle would drop the idle by 150 to 200 RPMs.

Newer LED headlights only draw about 4 to 5 amps, so way less drag on the alternator and engine.

Everything is a trade-off.

Risking an electric fan failure and roasting an engine may or may not be worth it.

On my 1st and 2nd 1986 22RE, and my heavily wheeled 1985 22R here in Arizona, I never experienced an issue where an electric fan would be a smart option.

Gnarls - that's just my opinion, it may be worthless.