Jeep 4.0 Dual Electric Fan Conversion
by Dino SavvaA stock 4.0 Jeep Cherokee XJ engine has two cooling fans. The main fan is a 15" diameter viscous clutch fan that is mounted to an engine-driven pulley. When the engine is cold, the fan freewheels and has little cooling effect. When the engine is hot, the clutch engages and the fan spins at a speed proportional to engine speed and keeps the engine cool.
The 11" diameter auxiliary fan is electric. It is triggered by a relay either when the A/C is switched on or when the engine temperature reaches 220*F (105*C). It switches off again either when the A/C is switched off or when the engine temperature has fallen back to 200*F (93*C). There are two problems with the stock clutch fan. The first is that when the engine is idling, the engine temperature reaches 220*F after a few minutes and the electric fan is triggered to switch on. Clearly the clutch fan isn't up to the job of keeping the engine cool enough by itself. The second is that when the clutch fan does engage, it makes a lot of noise and imposes a lot of drag on the engine (it weighs a hefty 5lb). This costs horsepower due to the engine driving the fan. Gas mileage is also reduced particularly in conditions where the clutch fan is most likely to engage i.e. city driving. An easy way to remedy these problems is to replace the clutch fan with an electric fan. The electric fan must have the following characteristics:
1. Fit behind the radiator as a "puller".
2. Be light and slim enough to clear the engine.
3. Pull in enough air to cool the engine.
4. Near silent operation.
5. Low current draw.
Finding a fan that fits within the confines of the engine bay with the 4.0 liter engine isn't easy. There is very little space. An electric fan assembly from another XJ is not slim enough. A Flex-a-lite #110 electric fan will fit, but it would have cost me close to 200 bucks including shipping.
I eventually found a fan in a local auto parts store. It was a 14" high performance reversible electric fan that could be mounted in either pusher or puller mode and it cost a mere 50 bucks. It's rated at 1800cfm in puller mode. At a little over 3" thick it was slim enough to mount to my XJ with plenty of clearance from the engine. It also weighed just 2lb so there was a useful weight saving over the clutch fan.
The next section shows how the installation went.
Installation
The first step is to remove the clutch fan and the fan shroud. If you remove the two bolts that hold the shroud onto the front clip, the shroud can be lifted up and over the fan to make more space to work in when it comes to removing the fan itself. Wear gloves when doing this because there's plenty of sharp edges on which you can cut your hands.
The clutch fan is held onto the pulley studs by four nuts. Once these nuts are removed, the fan will come off. The nuts have to be put back on the studs again and tightened to keep the pulley in place. You can then lift out both the shroud and the fan together from the engine bay.
The stock clutch fan shroud was re-used. I bolted the electric fan onto it using the mounting tabs that came with the fan. The only challenge was to get the fan completely shrouded and sitting as close to the radiator as possible for maximum cooling effect. All I had to do was cut four grooves in the edge of the shroud so the mounting tabs could be as far forwards as possible.
The shroud/fan assembly can now be bolted back in the same place that the shroud sat previously. This takes less than five minutes.
Voila! The installation is complete, and there's almost 1" of clearance between the fan and the idler pulley studs. Very neat.
The final step is to wire up the fan so that it operates in exactly the same fashion as the stock auxiliary electric fan. The aim was to have both fans working in tandem. This is where I enlisted the help of the friendly electrician at the local Jeep dealership. The fan was wired up so that it was triggered by a second relay (I had a spare relay handy) when the A/C is switched on or when the engine temperature reaches 220*F. This schematic (thanks Andy) shows how it's done. You can add a switch to operate the fans manually if you wish, but I didn't apply that option.
Results
How effective is the new fan?
Very effective indeed. Much better than the stock clutch fan! Operation is near silent. It operates simultaneously with the stock electric fan when the A/C is switched on. When the engine temperature reaches 220*F (only when idling or crawling with the A/C off), both fans switch on and in less than two minutes the temperature is down to 200*F whereupon the fans switch off again. You can watch the temperature gauge plummet as this happens! The current draw is very small, so there's no worry about draining the battery.
At speeds of 25mph and above, there is enough "ram air" cooling of the radiator so that the fans remain off. At highway speeds the engine runs at 180*F. In the summer (ambient temp. 120*F) with the A/C switched on, the engine temp. never rises above 220*F even when idling for long periods.
The engine now revs more freely. The horsepower and torque outputs have increased by an estimated 3hp/3lbft. The increase feels greater when the stock clutch fan would have otherwise engaged and imposed more drag on the engine.
Gas mileage in city driving increased from 18.4mpg to 19.8mpg. That's quite a difference!
My electric fan installation can be very easily reversed within a few minutes if I should decide to re-install the clutch fan. But then, why would I want to do that?
No doubt about it. This modification was an unqualified success and I'm thrilled with the results. I highly recommend it.
Updates
My original factory electric fan started to make grinding noises while I was driving into work yesterday. It had done this once before and it spontaneously resolved but this time it didn't. I found that the fan blades had become wobbly and the grinding noise was coming from the fan motor bearings. Time for a new fan, but not a straight replacement though.
The '97-'01 Cherokee fan (right) is reputed to be better than the older style fan so I wanted to see for myself. I managed to find one inexpensively from a motor factor dealing in Mopar/Jeep parts so I bought it. The new style fan has more blades than the old one and they are closer together so they should move more air. The shroud is exactly the same so it drops straight in. The wiring connector is different though, so I cut the connector and some length of wire from the old fan and spliced it onto the new fan's wiring. Installing the new fan was a breeze. It's slightly slimmer than the old fan so it's actually easier to manoeuvre into place.
The result? The new fan is much quieter than the old one. You can't hear it at all from inside the Jeep, but my coolant temperature gauge tells me that this fan certainly does the job of keeping the engine cool and happy!.