Rakkasan_Jeep

Well I did a little digging around about the 4.7's with the hydroboost system, or the hydraulic cooling fan system powered off the power steering pump and found something I didn't know.

I'm a culprit of this, but anytime you replace the power steering pump on the 4.7 with the hydroboost system, do not use your basic power steering fluid or ATF+4. My guess is the viscosity is to thick.

Coming from Chrysler, there is a specifically unique fluid that is required for these systems. It's MS5931.

I know from working on my Jeep recently that I have basic power steering fluid mixed with some ATF+4. Cooling system works fine when it's cool in the morning but once it warms up I do spike over 210. I've been beating my brains out over this for some time. So like I said, I did some digging around.

Since the hydroboost system is powered off the PS pump, the cooling fan runs off this as well, it would make sense a thinner viscosity fluid is used to move all the parts that rotate with the engine RPM's.

So it sounds like I'll be needing to flush the entire system and replace it with this type of fluid that is required for the 4.7.

I figure most of you already knew this, but if not, just a little FYI. Personally, I think I'll be going to the Dealership for this specific fluid and not the parts store for a fluid that matches it.

dave1123

Yeah, this is one of Chrysler's ideas to lighten the electrical load on the system. With all the electronics going into today's cars, some manufacturers have even thought about going to 24 volt systems. With my experience with aircraft, you can get some spectacular fireworks with 24 volts!

As with ANY hydraulic system, parts are expensive and you need a good working knowledge of how they function. Chrysler thought as long as the power steering pump is already running but not doing much, why not bleed off some pressure to drive the cooling fan? Good idea, bad for repair.

Rakkasan_Jeep

I 100% agree with you dave. I replaced the high pressure return line a few years back, and already replaced the PS pump. Problem is now, I have the wrong fluid in the system, but next week I plan on flushing it entirely out, when I can afford it financially.