New idea for running electric fans, how do I make it work?
 

So this is the idea. I already have 2 electric fans on my truck. And I really only need them on below 40mph. How would I set something up to turn the fans on when I go below 40 and turn them back off when I go over 40?
I was thinking of using a speed warning with a relay and setting the speed warning for 40. But unfortunately, I don't have the speed warning thingy on my truck.


Any other ideas for how I could accomplish this?

Todd

Since speed quickly translates into temperature due to air flow, why not just use a temp sensor? That way they're only on when the radiator needs them... which is rarely at speed.

Alternately, you could do an aftermarket speed sensor to turn them on and off. I suspect JC Whitney or other catalog-type place offers an add-on speed warning kit of some sort. Just use the output of the warning to kick over a relay to the fans, using the NC off the relay as the feed (so when the relay kicks over the feed loses power).

If you're trying to do something different for the novelty of it that's cool. However, I don't understand why MPH is the factor and not temp. Temp regulation is the entire purpose of the cooling system and maintenance of a certain operating range is the key, not MPH. If your engine is operating within that acceptable temp range and you are set up so your fan(s) work regardless of the temp just because you're under a pre-set MPH, you are just wasting amps and providing no benefit to the cooling system.

I bought a dual fan set-up from JEGS for my 402 BB and it uses a bulb sensor temp relay. I have a factory 4-bar radiator. Sometimes when I'm moving in slow, heavy traffic I notice they come on. However, even in the hot, humid, summer months of East Texas, they never come on when I'm moving at a descent speed, usually never comming on above 30-35 MPH.

The best thing I like about them is I have them set to run even after I shut the engine down. Depending on the day they may cycle twice after the truck is sitting. They do a good job of cooling that old big block down. I can also adjust the temp for the season in case I need my heater core to come alive faster when it's cold outside.

I had a single electric fan on my truck which wasn't enough to cool it but I think thats cause i got seperate problems. what I did though was I bought the sensor which I installed in the top of the radiator per the manufacturers instructions. I ran a wire straight off the battery to a toggle switch inside the cab so I could turn it off and on. From there the controlled juice wire went to the relay which was controlled by the sensor. I liked it like that because I could shut the fan off if i wanted to after shutting the truck off so I wouldn't possibly kill my battery.

What kinda cash did this little modification run? I like the idea of not running the belt driven fan all the time, that's gotta be at least a couple horsepower lost to that belt, and efficiency saves gas!

My setup...

and...

Now that aluminum fan holder is what I need. You wanna make another one and send it to me? lol

fuelcellguy made it to my specs. He did a superb job, was fast, and reasonably priced. Give him a shout.

The fans, wiring, relay, and everything else you need comes together. The total cost was around $250 with shipping. I have the twin 12's, Jeggs #400-210. It says they are only rated for V8's with up to 280 HP. However, I rarely drive in heavy stop and go traffic and I don't have a long commute.

If you drive in heavier traffic or a have a long stop and go commute, I would suggest the twin 15's. They pull up to 5500 cfm. The are Jeggs #400-290. The kit costs almost $400.

My setup was around $400 including the new 4-core radiator. On my plain jane 6-banger, the fans kick on less than twice per week... including stop and go traffic driving. The fans are wired in parallel so they kick on together, but are controlled by thermostat in the radiator. All the wiring and relays are inside the shroud, and are fused through the side of the shroud for easy servicing.

:hmm: I'M GETTING READY TO DO THIS TO "GQ" :gi:

I have a set of 14" flex a lites on a homemade shroud, with a painless wiring setup (on 185/off 170). The setup does a good job cooling my 383......if the truck is moving, the fans dont run much at all. They switch off/on in traffic.......69L

i have on 16 inch on my truck, its not enough i need too 10s or 12s

I don't know how it is in Texas, but that would never allow your engine to warm up on cold mornings. I the relay on mine riged to a constant hot, so the fan runs for a few minutes after I shut it off. I think it's cool cuz it gets people lookin, but i also read that it was good somewhere to help with distortion while the engine cools.

Unless you have it connected to an electric waterpump too, you are just cooling the radiator. Not that it is a bad thing, but the effect on the engine itself is minimal and even then it is more likely that just the fact that the air is moving under the hood is doing more for you.

The downside is that if the relay should happen to stick..........dead battery.

actually having the fans on will cool the coolant which will create a flow by itself. I am worried about the relay sticking issue though. I guess its a "flip a quarter" thing. the factory doesnt do this so it must be ok I suppose.
for fan control I suggest Ron Francis wire works. they have a real nice setup using dependable components. JMHO

The cooling system will still cycle if your cooling system holds good pressure even when the engine is stopped. Once the water in the block reaches the temp needed to trigger the thermostat it will empty the radiator into the block.

Mine will cycle at least twice on hot days and when the temp bulb senses the influx of hot water, the next load will be nice and cool.

I seriously doubt that there is any "flow". You may have some slight heat transfer, but it would be minimal and very hard to measure.
The fact that the system is pressurized is irrelevant. The pressure is equal in all directions so that wouldn't produce any flow..........unless you had a leak. LOL
The water pump moves the coolant....depending on convection isn't gonna do anything. Heat radiates in all directions not just up, but I don't think that you are going to get that "cooler" water from the lower hose to rise into the block either.

I would venture to say that your engine would cool faster by raising the hood than any other thing you could do.........short of an electric waterpump.

Letting the fan run certainly doesn't hurt anything....but I wouldn't depend on it helping much.

I don't think that "it is sensing hot water" by flow, It is the natural heat sink that raises the temp in the system. So it kicks on, cools the water in the radiator some and kicks back off. Then the natural underhood heat from the hot engine raises it back up again.

One word. Entropy.

Convection and radiation are doing more than anything.
If the fans were blowing outward they would do more in this situation, any heat pulled out of the radiator is being blown onto the hot engine. At least if it blew out, the engine's heat would be blown through the radiator on the way out.

I think people in parking lots would be a bit upset if it blew out though.....can you imagine walking by that and having the fans kick on? :lol:

So what you're saying is the forces of gravity, pressure, and a non-electric thermostat don't move the water in the system just because the engine is off? I can see your point about the pressure being equal throughout the whole system if it were a closed system. However, our cooling systems contain a certain amount of air and allow air to enter and exit. I would think the pressure release would allow for some amount of movement.

Maybe as the pressure is bleeding off there is some small amount of hot water moving through the top hose into the radiator. The sensor is routed through the opening for the top hose and hangs into the radiator about 2-4 inches. I would argue that when it is shut down heat sink is not activitating the sensor. If the fans do their job and cool the water in the radiator and there is no hot water comming back, they would never cycle after the engine is shut down.

Now you'll have me monitoring my temp gauge for a few days just to see if this is working or not. :lol:

There's a FAQ that covers putting in Nissan dual electric fans. The Nissan unit is perfectly sized for our radiators and has an embedded shroud. I'm in the process of finishing up this install tonight. < $75 for everything needed.

As far as flow without a pump, if the t'stat is open then as the water cools in the radiator it will become more dense, allowing it to sink and the hot water from the engine will rise. It's called natural circulation and is used in everything from nuclear reactors to furnace boilers.

http://67-72chevytrucks.com/vboard/s...d.php3?t=50085 is that the faq you're talking about? Yeah that looks easy enough to pull off. Reckon this mod would be good for a big block motor/headers/etc?