Question about Derale electric fan kit for Jeep Wrangler TJs

Juggernaut

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I tried to search but can only find info on Derale transmission coolers.

I've got a 1999 TJ Sahara the the original owner put a snow plow on and left it at their cabin in the garage most of it's life.
I bought it a couple years ago and was thrilled to have found a Jeep in the Black Hills of South Dakota that hasn't been off road!

A TJ isn't' exactly an ideal snow plow vehicle but it's been really useful that's for sure. When I drive it from my house to my cabin even running 55 MPH the plow blade blocks enough air that the Jeep will over heat. So I just added a Derale fan kit.


OK finally getting to the point of my post... LOL

The thermostat sensor for the kit engages the fan at 199.6 degrees and shuts off at 188.6 degrees. The measurements taken with my code reader.

I've read on here the 4.0L's operating temperature is ~195-210 degrees. Seems to me that the sensor is engaging the fan too soon and bring the temp too low.

So I emailed Derale to see if maybe I have a bad sensor or they packaged the wrong one in my kit. The guy answered back:

"If the temperature was verified at being over 190 and the sensor did not engage it would seem as though it is bad. We will need a proof of purchase sent to us that is within 1 year of the original date of purchase and we can send out a replacement."

In my mind that is going the wrong way, even cooler than what I think it should be at. Am I misunderstanding what is going on?

Anyone else on here have the Derale fan kit?
I use the Derale kit and had the same experience as you originally. The fan was running almost continuously as it would only shut off at about 185*. The solution was to purchase an adjustable thermostat in lieu of the simple thermal switch provided in the kit. It was about $60 through Derale. Now I have the fan kick on about 205* and off at 195*. Also a bit of advice is to change the provided fuse for an automatic resetting circuit breaker. Been running the fan kit for 4-5 years now without issue.
 

BuildBreakRepeat

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So now I know that the electric fan doesn't help anymore than the stock fan did.
That lines up with what most will say on here. At least the one who have the knowledge on these things. I would start by doing a complete system flush and visually inspecting for any leaks. Did you replace the thermostat with a non-failsafe OEM unit?
 

jscherb

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...It is reassuring to hear jscherb say he has no problems, I should have posted before I changed to an electric fan.
Do you have the stock water pump on your LJ? Could you post a pic of the blade up from the front of the Jeep just to see if your's maybe doesn't cover the same area as mine does? Just trying to eliminate different variables that might be affecting my Jeep...
I was traveling when you asked for the photo; I'm home and took this one today with the plow raised. Completely blocks the grille.

PlowRaised_zpsq6nnay2q.jpg
 

freedom_in_4low

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What is the downside of using an electric fan?
I don't have airflow numbers for the stock fan, but here's some general fan application info:
An electric fan is limited by how much current you can safely draw from the vehicle's electrical system without overtaxing it and draining the battery. At 12 volts, to power a 1hp fan would require nearly 70 amps, where as you can imagine a fan pulling 1hp off the engine would never be noticeable.

There are plenty of vehicles out there running electric fans with perfectly reliable and effective cooling systems, but radiators and fans are designed as a system. So a car designed to have an electric fan can easily add more fin surface, depth, etc to the radiator to make up any heat transfer lost to the reduced fan power and airflow.

It's when a radiator designed to use a mechanical fan gets matched with an electric fan that in all likelihood doesn't move as much air that we get in trouble.
 
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BuildBreakRepeat

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I don't have airflow numbers for the stock fan, but here's some general fan application info:
An electric fan is limited by how much current you can safely draw from the vehicle's electrical system without overtaxing it and draining the battery. At 12 volts, to power a 1hp fan would require nearly 70 amps, where as you can imagine a fan pulling 1hp off the engine would never be noticeable.

There are plenty of vehicles out there running electric fans with perfectly reliable and effective cooling systems, but radiators and fans are designed as a system. So a car designed to have an electric fan can easily add more fin surface, depth, etc to the radiator to make up any heat transfer lost to the reduced fan power and airflow.

It's when a radiator designed to use a mechanical fan gets matched with an electric fan that in all likelihood doesn't move as much air that we get in trouble.
Could it be possible to design an electric fan that mimics the flow numbers of the stock one?
 

freedom_in_4low

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Could it be possible to design an electric fan that mimics the flow numbers of the stock one?
It's definitely possible, but is it going to have a reasonable current draw?

the stock fan certainly leaves some room for efficiency improvement, so it's conceivable you could match the airflow with slightly less power, but here's just no getting around physics.

The highest airflow Derale fan I could find in 3 minutes on their website was a 17" that's advertised as 2400cfm, 23A and 0.35hp.

The commonly swapped Taurus electric fan is cited as moving 4500cfm and drawing about 33A. Assuming an 80% efficient motor and a 50% efficient fan (which is typical for an axial propeller fan and giving some extra credit on the motor) that works out to 0.53hp at a pressure drop of 0.3 in H2O. To match that with a prop fan would only pull 0.42hp from the belt. This is probably about the limit of what an electric fan can do without major electrical considerations, and again I don't have the stock airflow numbers but being in excess of 4500cfm is well within the realm of possibility.

Power input for a given fan increases with the cube of airflow. So just a 25% increase in airflow almost doubles your current draw.

The great thing about an engine driven clutch fan is that more airflow is basically free...there's no extra material because you just have to pitch the blades a little deeper, and it's really small potatoes on your EPA mpg because at speed the clutch is disengaged. The first limit you'd run into is the power transmission capacity of the serpentine belt.
 
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BuildBreakRepeat

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It's definitely possible, but is it going to have a reasonable current draw?

the stock fan certainly leaves some room for efficiency improvement, so it's conceivable you could match the airflow with slightly less power, but here's just no getting around physics.

The highest airflow Derale fan I could find in 3 minutes on their website was a 17" that's advertised as 2400cfm, 23A and 0.35hp.

The commonly swapped Taurus electric fan is cited as moving 4500cfm and drawing about 33A. Assuming an 80% efficient motor and a 50% efficient fan (which is typical for an axial propeller fan and giving some extra credit on the motor) that works out to 0.53hp at a pressure drop of 0.3 in H2O. To match that with a prop fan would only pull 0.42hp from the belt. This is probably about the limit of what an electric fan can do without major electrical considerations, and again I don't have the stock airflow numbers but being in excess of 4500cfm is well within the realm of possibility.

Power input for a given fan increases with the cube of airflow. So just a 25% increase in airflow almost doubles your current draw.

The great thing about an engine driven clutch fan is that more airflow is basically free...there's no extra material because you just have to pitch the blades a little deeper, and it's really small potatoes on your EPA mpg because at speed the clutch is disengaged. The first limit you'd run into is the power transmission capacity of the serpentine belt.
That’s what I figured. I like knowing the science behind the commonly recommended routes.
 
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jlpierce70

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I use the Derale kit and had the same experience as you originally. The fan was running almost continuously as it would only shut off at about 185*. The solution was to purchase an adjustable thermostat in lieu of the simple thermal switch provided in the kit. It was about $60 through Derale. Now I have the fan kick on about 205* and off at 195*. Also a bit of advice is to change the provided fuse for an automatic resetting circuit breaker. Been running the fan kit for 4-5 years now without issue.

Some of the reviews I've read about the kit is that the fan goes out after a year or so. That makes sense if you use your Jeep for a daily driver the way the fan is always turning on, running for a few seconds and off again. I have to think the start up is the hardest on the fan, the relay, and the fuse.

Good to hear there is an alternative to the basic temp sensor switch.
 
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jlpierce70

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That lines up with what most will say on here. At least the one who have the knowledge on these things. I would start by doing a complete system flush and visually inspecting for any leaks. Did you replace the thermostat with a non-failsafe OEM unit?

Knowing me I got the thermostat from O'Reily's so I'm guessing not OEM.

No leaks. My plan is to do a full flush when I have time. My Jeep isn't my daily driver so that helps, and I want to make sure if I need it to plow before I have a guest arrive at my cabin its ready. So I might just put this on hold until we are well into spring.

My Polaris General has been in my garage for a couple months for a few projects that should have taken me a few days of solid effort. Too many irons in the fire! If I get after that project and get it out of the way I might jump on the Jeep then depending on the weather and what work looks like.
 
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Juggernaut

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Some of the reviews I've read about the kit is that the fan goes out after a year or so. That makes sense if you use your Jeep for a daily driver the way the fan is always turning on, running for a few seconds and off again. I have to think the start up is the hardest on the fan, the relay, and the fuse.

Good to hear there is an alternative to the basic temp sensor switch.

The fan motor itself is made by Spal which is a very common manufacturer of OEM products and is reliable. From my experience the trouble with the stock thermal switch is that even at highway speeds where there was ample airflow, the fan wouldn't turn off because of the switch's low temp setting which is below the operating temp for our motor. I'm speculating that the highway wind speed added resistance to the fan as it would blow the fuse fairly routinely after a long haul (hours) on the highway with hills. It never blew the fuse at startup which should have been the biggest draw, even in a stop and go traffic condition. Anyway the programmable thermostat solved that and the resettable breaker is bit of insurance against a blown fuse and a no fan condition.
 

ejay

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FF Dynamics makes an awesome electric fan kit with aluminum housing for $300 shipped. I've had it in my cart for a while but haven't pulled the trigger on it. Has a cut off switch for water crossing, too. yaaaayyy.....

In regard to electric fans being a bad idea: In my eyes, there is less resistance and noise than a clutch fan. Some people claim you get better gas mileage but I'm not sure that's true at all. You can push more air during the hot summer days as well. I can see it being an advantage if you're crawling with the A/C on or towing at slow speeds I guess. Hardly any natural air movement then. Having never tested this, I wouldn't know how effective it was in practical applications. Most kits have an adjustable heat sensor that can turn it on and off at your own settings.

Reality is, I have hood louvers. The only reason at this point in my life that I would need more air flow is to cool the firewall. I've yet to heat shield the cab side of the firewall and that area sometimes gets hot during my longer trips and leads to sweaty feet syndrome. The louvers didn't help much in that regard. Don't know if pushing more air would either. I don't plow snow but I can most certainly see why artificial means of air flow would be an advantage for the OP. Replacing something mechanical with something electrical just means it's one more thing that can go wrong. Not that those clutch fans are bullet proof. The last store brand I purchased started leaking a few years in.
 
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jlpierce70

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Update:
I drained the radiator, then used Prestone radiator flush and cleaner. Two bottles when one would have probably been enough. Drove it for a few days, didn't do the 10 min flush. Drained that out and ran water for a day to flush the flush. Then put new coolant and a new thermostat in. I'm guessing the thermostat was fine but seemed dumb not to do it anyway.

I also ordered the Derale 16749 adjustable fan controller. While I was waiting for it to arrive I unplugged the fan sensor and had it rigged that I could turn it on manually with the green trigger wire. Never had to. Even on 50 degree days it stayed right at 210 without any help from the fan both in town and highway driving. Probably a dumb idea but was tired of the constant on/off of the electric fan.

When I was putting in the new thermostat I got rid of the adapter/sensor that came with the fan kit original but had to make my own to make the screw in sensor work. (16749 screw in sensor--16759 push in sensor). I just wasn't thrilled with results I was getting with the readings on the dash temp gauge or the behavior of the fan control so I ordered a push in sensor and again ran without any fan without issue. I bleed the adapter by unscrewing one of the sensors until coolant only came out so I don't think I had an air bubble in the adapter I made. The temp the gauge showed was way cooler than what the engine was judging by feel, smell and using a thermal temp gun.

I got the push in probe yesterday and got it installed. Now just trying to dial in the turn on setting.

I know the "electric fans are bad" guys are thinking I'm sure a glutton for punishment considering after I did the flush I probably could have just put the stock fan/clutch/shroud back on and been just fine rather than buying more and more stuff. Momma didn't raise a quitter I guess! I kind of enjoy the challenge of making this work.
 
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jlpierce70

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I use the Derale kit and had the same experience as you originally. The fan was running almost continuously as it would only shut off at about 185*. The solution was to purchase an adjustable thermostat in lieu of the simple thermal switch provided in the kit. It was about $60 through Derale. Now I have the fan kick on about 205* and off at 195*. Also a bit of advice is to change the provided fuse for an automatic resetting circuit breaker. Been running the fan kit for 4-5 years now without issue.
I took your advice and added an auto resetting circuit breaker. Not thrilled that Derale used the same color wires for different things from the regular kit (positive switched) to the manual control kit (negative switched). I had the original done with all matching wire colors, and really did a professional job of it. Now red key'd power goes from red to yellow. Its all in wire loom but someday when I die and my Jeep finds a new home if they take it apart they'll wonder what the hell I was thinking!

Did you go with the screw in probe or the push in?

If push in, where did you put the probe on the radiator? I did it where they said to, by the hose coming from the thermostat.

I'm not getting real consistent turn on and off temps. And the instructions say it turns off 10 degrees lower than the turn on temp and I'm seeing it continue to run much longer/lower than that. I called them yesterday but no answer, probably off for the virus. I'll see if they email me back.
 
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jlpierce70

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I called and they are there today. Tech support says that the replacement push in probe is correct for the controller I have and what I'm describing sounds like its working. That measuring temp with my code reader, seeing it drop to whatever temp may not be what the probe is seeing.

The stock sensor is on the thermostat housing and the probe is pushed in near were the hose from the thermostat hooks to the radiator. So I'd think the temp would be fairly close but I'm not sure how the water is distributed between the cores of the radiator after it goes through the entrance that the top hose hooks on.

I'll play with it a little more and see what I figure out. At worst I still have all the stock parts if I decide its not going to work for me.
 

Juggernaut

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I use a push in probe with touch of hi temp silicone to secure it in place for added security. My other car uses the same controller with an adapter and probe in the upper radiator hose - I don't recall the manufacturer. I labored over where to mount the push in and after some experimentation, I came to the conclusion that it doesn't matter as the probe and the controller don't see an actual temperature, just a voltage to turn on and off. Mine is current upper passenger side. The important part is setting the dial on the controller to hold the desired engine temp. Using a scanner (not the analog dash guage), I set the controller to kick the fan on about 212, turning off at roughly 202. It did take a few tries to get it dialed in, but the on/off is fairly consistent and I suspect in the same range as the fan clutch as my engine temps vary the same amount with both fan setups.
 

Feralkid

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The electric fan functions to cool off the radiator.

Therefore, the temperature probe should be placed in a position to measure the performance of the radiator as it lowers the temperature of the coolant.

That place is the lower radiator hose where the coolant leaves the radiator and enters the engine.

Any other spots will cause the fan to run more often than it needs to, which effectively eliminate the entire purpose of an electric fan.
 

Juggernaut

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The electric fan functions to cool off the radiator.

Therefore, the temperature probe should be placed in a position to measure the performance of the radiator as it lowers the temperature of the coolant.

That place is the lower radiator hose where the coolant leaves the radiator and enters the engine.

Any other spots will cause the fan to run more often than it needs to, which effectively eliminate the entire purpose of an electric fan.
There's a different school of thought on what you said about the location. The temperature of the coolant after it exits the thermostat housing (where the factory temperature sensor is located) is most indicative of the engines operating temperature. You want to control the engine temperature not assess the heat transfer of you radiator, so the upper hose, radiator or thermostat housing is the most accurate location. The manufacture suggests this as well.
 
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Feralkid

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There's a different school of thought on what you said about the location. The temperature of the coolant after it exits the thermostat housing (where the factory temperature sensor is located) is most indicative of the engines operating temperature. You want to control the engine temperature not assess the heat transfer of you radiator, so the upper hose, radiator or thermostat housing is the most accurate location. The manufacture suggests this as well.
Which manufacturer?

You know, anyone can throw a kit together with chinese parts and call themselves a "manufacturer".

I found a deal on craigslist for one of them there flexalite E fans. $100.

Fan is oem quality.

Controller= shit box leaking diarrhea

After much research, I discovered that the only purpose for a fan being there at all is to service the radiator, not the engine.

When you are traveling at 50 mph the ram air through the radiator is much higher than a fan could produce. In that state the fan should be off.

If you measure the water temp at the engine exit the fan will run at 50 mph.

The way the manufacturer suggests would make the fan operation a function of engine rpm.

The way I suggest, makes the fan operation a function of cooling necessity. The fan only operates when increased heat needs to be dissipated from the radiator.

In 80* F weather, idling my fan runs 20 sec on, 100 sec off.

When I'm moving above 15mph it stays off unless I rev the rpms up past 3500.

Over 30 mph it stays off 100% of the time.

Also, a fan will wear out faster the longer it operates continuously.
Think about it.