I think having the fan come on at 180 degrees is not at all necessary, and may actually prevent your engine from reaching the combusting temps that allow it to operate as efficiently as it it can. On my setup, I have the low-speed fan cut in at around 200, which keeps the coolant temp down to between 195-205 degrees. This way, the fan only runs when the truck is hot and moving at low speeds (not uphill), and doesn't run while cruising at all. This saves the gas that runs the fan.

I have the two speed mercury villager fan. This allowed me to wire up the high-speed fan to the air conditioner cut-in, which is also an emergency ON switch for the fan.

I have a Hayden type thermo switch that senses the coolant temp from within the hose coming from the engine into the top of the radiator for accurate readings. I used some quality bosch heavy duty 50 amp relays and wired diodes onto the fan leads to help prevent the relay's arcing on fan startups. I also wired up an electrical coolant gauge into the cabin that takes its coolant temp readings at the same place as the thermo switch with a low and high fan indicator LEDs so I know exactly at what temp the fan is coming on and shutting off. I mounted the brand new fan ($45 off ebay) into the stock shroud for maximum pull and minimal screwing around.

Since this mod, I am saving 1.5-2 mpg, which is about 10%, and that ain't bad at $3 bucks plus a gallon! The quiet is nice too. I think I spent a total of $100-120 for the mod.

 

DJ99, sounds like you're running a setup very similar to mine, although mine's a 22re. I recently installed a light to show me when the fan is running. The temp sensor (mechanical) in the t-stat housing shows me the coolant outlet temps. I have a couple of observations to share and I'd appreciate anyone's input:

1) Using the ambient-air sensor on the relay gives different kick-on temps for city vs highway driving. The sensor is zip-tied to the back of the radiator pretty close to the inlet. At low speeds, it causes the fan to come on around 200F. On the highway (doing about 65-70) it causes the fan to come on at 210F. I guess this is due to more convection over the sensor at highway speeds, causing it to decide it is "hot enough" at higher coolant temps.

2) As a corollay thought, the fan DOES come on when on the highway occasionally. It is directly related to the outside air temp. On a crisp morning (30F) the fan never comes on. Any warmer than that, and the fan will run sometimes. The temp gauge hits 210, it comes on, brings the temp down to 200 or 205 in about 10-15 seconds, and then usually stays off for 60 seconds. Have you all had similar experiences? I had assumed the fan would never need to come on in highway driving, but I guess it's not really a problem...

 

I have one temp sensor and it is situated in the radiator, typical of most Efan installs.
As far as I am concerned, the cooling system shouldn't care what ambient temperature is, the system should only be concerned with interior engine temperature.

I read all the above comments, am I missing something?

I need to hook up my LED for fan 'in use' notification, so I can't comment on what my system is doing while on the hwy.

As a side note, I believe that running an Efan with too low a temperature turn on will not allow the auto-trans to shift correctly because the fluid isn't getting to operating temperature. I could be wrong, but I thought the fluid is constantly flowing thru the radiator unlike the engine thermostat that shuts off the flow to the radiator to maintain proper operating temperature. I have an a/t and noticed this issue. I have also noticed a change in the heat(blower) when the efan kicks on to early, I can actually feel the temperature change in the truck when the thermostat opens, I'm guessing this can't be good for the engine to get a 'shock of much cooler fluid(but my heater core has also been clogged in the past, so I could be way off with this assumption).
With that said, you thermostat will control operating temperature regardless of when your fan kicks on or how cold the ambient temperature is presently.

please correct me if I'm wrong.

 

Not really, that's the job of the t-stat. If too cool the t-stat (assuming its working properly) bypasses the whole radiator making the fan irrelevant.

 

Exactly on the t-stat funtion. But I think you're over-thinking the ATF temp effect on shifting. Mine shifts just fine through a wide range of ATF temps.

 

Dale,
I don't want to get off topic, but, i thought the ATF needs to get up to a certain temp to shift into O/D? I've experienced this with my (new to me) 88 and back in 1990 i bought a low mileage 87. I know the 88 needs the solenoids(hi-miles on the clock) which is why it behaves the way it does, but the 87 would always take a mile or two to shift into O/D on my morning commutes.

 

AFAIK its the coolant that needs to get up to a certain temp to shift into OD. Right thinking, but I believe its the wrong fluid.

 

OK, that seems to make more sense, thanks for clearing that up, now back to our regularly scheduled program.