Do me a favor guys and look at your radiator cooling fans for me. I am trying to figure something out.

My Grand Cherokee Overland has a HYDRAULIC FAN! Got damn lines coming from the damn power steering pump!

I'm trying to figure out if this is a 4.7 thing, a 4.7 H.O. thing, a Jeep GC only thing, or a Jeep GC Overland H.O. thing.

This is what I've found out so far in researching over the 'net & Jeep sites.

The fan speed is controlled by the PCM and is a Pulse Width Modulated signal to the solenoid. The PCM controls fan speed based on four different conditions...
1. Engine Coolant Temperature
2. Transmission Oil Temperature
3. Battery Temperature
4. A/C System Pressure

Also, for any REAL mechanic types (I'm just the shade tree type), what are the advantages (if any) and disadvantages (besides the obvious fluid leak means fan don't spin) of this setup as opposed to a conventional clutch type or an e-fan?

 

Chrysler bagan using this on a bunch of platforms. The Inline 6's however used a Hybrid fan which is a combonation of a clutch and electric set-up.
The hydralic set-ups are used for less power consumption and increased towing capabilities for any cooling issue's that may arise. 4.7/5.7 have this style.
The fan unit and motor assebly are not serviceable since they are balanced matched to each other. They must be replaced in one complete unit. You can change out the lines if that's the problem however, there is a valve that is inside the fan motor that controls flow and if it fails you will experience hard steering.
This set-up doesn't create any drain on the battery as a fully electric unit would. There is a way to check it all with a scan tool, but I'm not sure how that works exactly. It's pretty much all by ear and there's no specific read-out.
Also, there's no simple way to check the fluid level either. it's one of those ingenious designs by yet another dumb engineer. I would have atleast create a sight window!

If your fan isn't spinning, that isn't good news. That means your solonoid valve (same type that's in a power steering pump) has failed and you need a complete whole new unit. That means the Fan, Fan shroud, Fan motor and casing are all one unit. A minor leak wouldn't stop the fan from spinning, just that solonoid valve would. That's the disadvatage here, but then again, it's the same with electric fans and clutch fans.

 

Just for reference, I know Lexus was the first to use this set-up in 92 or 93 in their sports car. What ever it is a 300 or some crap. Glorified Toyota!..lol Toyota uses this in their Camry's as well.

 

Thanks 'dog. Mines not giving me a lick of trouble, I was just shocked to see it, that's all. I probably had the thing for about 6-8 months, been under the hood probably half a dozen times before I noticed it. I saw there was no belt going to it and no clutch fan right away, but with only slight glances, thought it was an e-fan.
A couple of months ago, while pouring in some RP 10w-30 during an oil change, I just happened to glimpse the hydraulic lines and traced them back to the power steering pump. I was like WTF?????

Oh and just FYI, I did a little research on it today after I posted this, there is a TSB out on it that as of early '07 you no longer need to replace the whole unit in case of solenoid failure. Separate part now, at least for the WJ's ('99-'04) although it appears the hydraulic fan did not start until the '01s. They do advise that you have the new solenoid close by when removing the old one to minimize PS Fluid loss though.

According to the site I got the above information from, cooling was an issue on the WJ's with a conventional clutch-type fan. Sometimes while towing, but more specifically while towing if you had an aftermarket bully or push type bar on the Jeep. Seems an air dam was needed from day one to specifically draw additional air up, across the radiator from underneath. Anything installed that would interrupt the flow from down low caused issues, mainly when towing.
The additional cooling capability of the hydraulic setup and the use of a much larger fan fixed this issue. An added benefit is when they went to the hydraulic setup, they didn't need the air flow from underneath and it allowed them to protect the lower radiator/tranny cooler from debris when off road, a major complaint from those with the clutch type fan and air dam...

 

About time they came up with individual parts. That solonoid valve is just a small piece to the puzzle and was causing lots of issue's. Especially for the people who don't flush their Power steering fluid when it's suppose to be.

If your fan stops working, the first thing you should do is check the fluid and make sure it's not low. Then go from there.

Glad to hear you could find anything out there on that stuff! It's one of those, hidden things most don't know about....until there's failure!