Off road, and in stop-n-go traffic, the cooling fan on the JK comes on to cool the radiator when the water temperature reaches 215°F. It brings the temperature down to about 195°F, and turns off. The cycle continues until there is sufficient air flow from forward movement to keep the water cool without the fan.
There’s nothing so bad about that from the engine’s point of view.
However, until the fan comes on, things in the engine bay can get quite hot, including intake air temperature. The automatic transmission fluid temperature will also climb during the time the fan is off, even if there is an aux cooler installed. The aux cooler may prevent the transmission from overheating, but the fluid temperature can still get quite high when compared to the temps with sufficient forward movement.
I have been monitoring the temperatures of the engine, transmission (with an aux cooler), and intake air. The engine takes air from the engine bay, so I’m using intake air temp to reflect the approximate engine bay temperature.
With all that in mind, I decided it was time to cool everything down a bit.
The only item I could think of that would address all of the temperatures listed above is a fan that turns all the time the engine is running.
I thought about adding a switched ground wire in the fan high speed relay circuit. That would work, while off road and in traffic, but the driver would have to remember to turn it on, and off when on the road. How long will the electric motor last with the extended run time?
The idea of a mechanical fan seemed like a good idea. There would always be air flowing through the transmission aux cooler, the A/C condenser, the radiator, and the engine bay. It seemed ideal.
After a little research on the forum and elsewhere, I came up with all the parts to convert from electric cooling to mechanical cooling, (kind of retro, I know).
The fan and shroud are specifically designed for the pre-2012 JK. There is also a MOPAR fan clutch available for the JK, but it’s over twice the price of the generic clutch. If there is a longevity issue, I’ll try the MOPAR fan clutch.
Everything in the photo below is an easy plug-n-ply installation. It took about 1 hour from opening the hood to driving off for an ops check. Like I mentioned, it’s all designed for the JK. The stock electric fan comes out. The new fan and shroud go in.
For now, I’m going with the mechanical fan and shroud. There is also an electric fan designed to work with the shroud, for added cooling in extremely hot locations. The mounting points for it are on the stock radiator frame. The JKs shipped to the Mideast have the electric fan, shroud, and mechanical fan.
I don’t think the additional electric fan is necessary for the U.S. But, the option is there for those who want to have a lot of extra cooling capacity.
The mechanical fan and shroud have been installed for only a day, so I can post only preliminary results.
There is additional noise when the engine is first started. Once the fluid in the fan clutch moves to the proper chamber, it quiets down to nearly stock. On a cold start, it takes about a minute or two. On a hot start, it takes about 30 seconds.
The temps here have been in the 60’sF.
I’ll list the vehicle’s temps under similar conditions before and after the conversion. These are off road and in-town traffic conditions.
There is no real difference on the highway, as there is plenty of air from the forward movement.
Since I wrote the preceding sentence, I have learned the automatic transmission stays cooler on the highway, too.
My theory is, the fan creates a low pressure area behind the radiator, which allows more air to flow through the cooler, condenser, and radiator.
Before, the engine temp would cycle up and down between 195°F and 215°F
After, the engine temp stays at 195°, ± a few degrees.
Before, the trans temp would climb to about 140°F.
After, the trans temp stayed below 120°F.
Before, the intake air temp would climb to 165°F+.
After, the intake air temps stayed below 115°F. (I’m assuming this also indicates lower engine bay temps.)
Before, opening the hood following a moderate idling period, there seemed to be a lot of heat in the engine bay.
After, opening the hood following a moderate idling period, the heat seemed to be a lot less, and there was a nice breeze blowing over the engine from the fan.
Before, overall average gas mileage was around 18.5 mpg.
After, (well, it’s too soon to tell).
The parts involved:
The fan installed on the water pump:
The finished product:
Photo of the stock fan, and the fan used with the mechanical fan and shroud, if max cooling is needed: