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Power steering cooler and cavitation during winter

Agreen, thank you for your comment.

1a) I wasn't aware that there is some sort of restriction in the trans cooler. A "tube that's flat?" You mean the bends of the pipe going back and forth? So perhaps these "feet of head" is causing too much back pressure to operate properly? I got the idea to use the stock trans cooler as a PS cooler from some youtube videos. Perhaps this wasn't a great idea after all?

1b) Are you sure the transmission cooler's pressure is lower than the low-pressure side of the power steering system? Isn't the highest pressure of the power steering's low-pressure side no more than around 50-100 PSI? The transmission cooler hoses that are sold have a max of 400 PSI, while the low-pressure power steering hoses tend to be 200 PSI.

2) The plumbing of the power steering system is such that the:

PUMP (1050 PSI) ----> GEARBOX (high pressure side) --[internal]--> GEARBOX (low pressure side) ----> COOLER (bottom) --[internal]--> COOLER (top) ----> RESERVOIR ----> PUMP

Is this the correct routing?
 
Oh yeah if it's return pressure then it's hardly anything at all. And yeah, that's the correct routing.

Transmission line pressure is like 100 psi. It's not as much as you'd think.

The transmission cooler is literally a flattened tube that is spiraled inside the end tank of the radiator. I personally wouldn't have used the radiator cooler because I'd think it's probably adding more heat to your PS system than removing it. In all my years I've never touched a stock power steering "cooler" (which is a short loop of steel tubing) and gone "damn that's hot!!". But I have been burned by radiators though. Maybe there's some engineering aspect that I haven't considered, but I also know that every time a car came to our shop for a transmission rebuild, we would bypass the factory trans cooler and install a tube and fin cooler on it to keep the transmission temps down. Heat will kill a transmission quickly, and being down south where air temps get in the 100's routinely, I wasn't taking the chance. Call it luck, call it overkill, but we never had a customer return with a burned up transmission.

I still think I missed the point of why you didn't use the stock cooler (lower case p-shaped tube)? You said it's because you're using a lunchbox locker in the front, but I'm not seeing why that has anything to do with power steering coolers. Maybe if you were using hydraulic assist steering you might need more cooling, but having a lunchbox locker really doesn't have any bearing on that IMO.
 
1) the trans cooler inside the radiator is a tube that's flat and can cause restriction so that could be an issue. Power steering pressure is higher than transmission line pressure.
2) if you have the cooler hooked up backwards it will definitely cause cavitation. If you have it plumbed to supply pressure to the top of the cooler and return from the bottom, you're creating a waterfall effect with the PS fluid. Make sure it goes bottom to top, THEN returns to the PS pump reservoir.

1) I assume he is using the stock auxiliary tranny cooler for power steering rather than the radiator water cooled one. Jeeps sold with the tow package had a tube and fin two pass cooler for the transmission, maybe a bit more than a foot long, it was mounted horizontally down near bottom of radiator, in front of radiator, it is an air cooled cooler.

So which is it, water cooled cooler, or auxiliary towing air cooled cooler?

2) 100% correct, since air rises over the fluid, always have the supply line at low
point, and return at high point do not mount in such a way to cause an air trap i.e. an inverted U in the system. Thus the stock two pass tube cooler is mounted horizontally. The supply (inlet) to this cooler should be the lower fitting, the return (outlet) is the upper fitting
 
Agreen, the Powertrax no-slip front locker puts noticable stress on the power steering pump when the locker is engaged. You can witness this when you try to make a turn, there is considerable resistance as the wheels want to return to centre, otherwise there must be slip between the tyre and ground on a turn. While in 2WD, there isn't any added stress on the power steering system, but when engaged, it is considerable from what I've witnessed.

After installing the locker, I took my Jeep wheeling and after a few hours, my original 2006 era high-flow AGR pump started leaking. I never had an issue with that pump for over a decade until I put the locker in. This is why I decided to add some sort of cooler to the power steering system once I replaced the AGR pump with the Lee pump.
 
Oh, AGR! Run away. A long time ago they had a decent reputation. Now days it is a new owner,
away from them Aholes. They tried to rip me off, sent me a junk gearbox, wrong size, then over billed me higher than the invoice. Then wanted me to pay to send it back. I stopped the credit card payment on them jerks. Rip off, run away! crooked thieving liars. AGR, = junk.
 
Sorry, but I don't quite follow your question. The transmission oil cooler, which is being used as the power steering cooler, is mounted in the factory location. Whatever level that stock placement is, is where the radiator is. You are asking if the top of this stock trans. radiator is at a higher elevation than the power steering reservoir level. If not, make sure it is. But then your next line says to make sure the reservoir is higher than everything else in the system. This looks like a contradiction. Could you please clarify? The reservoir is the power steering component with the highest elevation.

I don't see any sign of a vent in the Lee Power Steering reservoir cap. This is what the Lee pump and reservoir look like: https://leepowersteering.com/collec...w-hi-flow-pump-kit-jeep-cherokee-xj-1987-2001

In the description on the Lee website, it says the pump/reservoir "includes our Zero Cavitation reservoir with pressurized no leak cap that is perfect for aggressive wheeling." So it sounds to me like the reservoir is NOT supposed to be vented. Apparently the reservoir has some special flow design which is supposed to make it not cavitate. How well that works, I don't know.

You need a vented cap or other method to expel the bubbles in the reservoir (drill and tap a nipple for a vent hose).

The increased pressure in the system is expansion of the normal bubbles in the fluid as it heats up, causing the cavitation as the fluid drops pressure in the gear box, because the bubbles cannot escape in the tank as the pressure keeps the vapor mixed in the fluid (much like the CO2 in a beer bottle stays suspended in the beer under pressure... until vented).

Lee's hi pressure / low cavitation claims defy the physics of partial pressures at the pressure drop through the gear box.

BTW, my 88 has identical return line routing through the factory tube fin tow package cooler (the AW4 has a larger cooler). Stock style pump, gear box, and ZJ links, on 33x12.5's with no cavitation (for 20 years).
 
Ed A. Stevens: Thank you for your comments. I appreciate it.

My guess is that the Lee reservoir is not fully pressurised to pump pressure. 1K PSI would be way too high. The reservoir must be at some lower pressure, perhaps 30 PSI? Under the reservoir cap there is a flat washer-like spring, which provides back pressure to the user when they press the cap down onto the reservoir, and under the spring is a large rubber seal, which is just a wide flat rubber washer. Perhaps this combination cannot form a prefect seal - I mean, that spring would have to be fully flattened and even then, the metal-to-metal part of the sprint-to-cap won't completely seal. But as I hear a pop when removing the cap, we know that the reservoir is not at atmospheric pressure (ATM).

This begs the question, what minimum pressure in such a system is needed for air to come out of solution (ps fluid)? Perhaps whatever pressure remains in the reservoir is still low enough for air to come out of solution, that is, since the fluid in the gear box is pressurised, wouldn't you only need the reservoir pressure to be lower than the gear box pressure for air to escape [into the pressurised air of the reservoir]? Obviously, the greater the pressure delta, the faster the air escapes. Note that the top half of the reservoir is meant to be left as air.

I cannot imagine that with all the vehicles that Lee supplies that they have such a basic flaw in their design. Perhaps the wording on their website can be interpreted incorrectly.

There was no issue driving the Jeep today, which was surprising. However, I still intend to drive it with the rubber washer removed from the cap to see if it feels any different.
 
Update:

I pulled the tranny/PS cooler hoses and capped them using a metal rod and a hose clamp (left it filled with PS fluid). I replaced the factory pipe/hose for both the high pressure and return lines using the Edelmann Elite product. Bled the air. Two days driving and no issue whatsoever. It drives like a brand new car. Morning starts are fine now. The back pressure created from the tranny radiator and 8' total of extra tubing was likely the cause of the cavitation.

For cooling, I have wired the AUX fan to the FOG SWITCH since I haven't had fog lights installed since putting on the ARB front bumper.

I hooked the AUX fan up to my equipment on the bench, and at 14 V, it draws 4.75 A. The fog lights, anyone know what wattage they are? Perhaps 55 W each? So that would be about 7.5 A total. Looks like there is a 15 A fuse in the PDC which is for the relay that feds the fogs, so this should be good enough to blow in the event of a fan failure (short). Note that the control to the fog relay is the headlamp switch, meaning that the fog light current does not flow through the headlamp switch, so there is no fear in blowing the headlamps if the fan fails. This was my main concern with this mod.

My plan is to run the AUX fan when wheeling in 4WD and hope this is sufficient to cool the PS pump. As noted previously, the front no-slip auto locker puts a lot of strain on the PS system. The Lee aluminium reservoir acts as a heatsink. Lee does have a finned version of the reservoir I suppose I could swap if I wanted more cooling.

Anyway, I got the idea to use the tranny cooler as a PS cooler from some Navy guy's youtube video. He also had a Cherokee. I wonder how his mod is working out...
 
Ford super duty trucks have a pretty good stock transmission cooler if you're still looking for something to put there. I'd just grab a small Hayden trans cooler and use that. Those use a larger diameter tube than the factory XJ cooler does, I believe.

Glad you finally got an answer.
 
Thanks for the info, however I think my foray into power steering coolers ends here, for the time being anyway. If I blow another power steering pump on the trail, I'll have to re-evaluate the situation. I probably won't even remove the Dorman sitting in the front of the other radiators as I'd have to find a place in the garage to store the darn thing.
 
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