Most of us are pretty conscientious about doing regular maintenance to our vehicles. On the underside, we check fluid levels and change them at the appropriate intervals: these include the transmission, transfer case, and front and rear axles. We lube the U-joints and steering components. Under the hood, we check or change the engine oil, brake fluid, coolant, and power-steering fluid.
But let's stop right here at the last one-power-steering fluid. The drill is to unscrew the cap off the pump/reservoir and take a look at the fluid level as marked on the attached dipstick. Yep, right where it's supposed to be; and why wouldn't it be? Unless you have a leak, which would be pretty obvious, there is nowhere for the fluid to go. The steering system doesn't burn oil, nor does it evaporate, and in fact it could be a sealed system, and in practicality it really is.
But think back, when was the last time you changed the fluid? My bet is, never! Generally, you won't even see a mention in an owner's manual about changing power-steering fluid; or if there is one, it will be like at 50,000 to 60,000 miles. In reality, miles aren't the important factor here. Pump operation time and heat are the deciding factors on a vehicle used off the highway.
Most roads are laid out in straight lines. When you're driving down them, very little turning takes place, which means very little fluid is being moved and for the most part the power-steering pump is just idling along doing no work. But let's hit the trail: now we're constantly turning the wheel, making that power-steering pump earn its keep. Not only that, but it has to work a lot harder on the trail than it ever did on the highway. Not only does it have to overcome trail obstacles, it has to fight against a much wider tire footprint and a tire that is driving, instead of just being pushed along.
Pressures can reach well over 1,200 psi and fluid temperatures in excess of 300 degrees F. Petroleum-based lubricants don't like temperatures much over 230 degrees. When the power-steering fluid breaks down, metal-to-metal contact takes place with resulting wear. Now we have small pieces of metal circulating within the system causing even more wear.
Solutions? Number one is to make a habit of changing out the fluid once a year. Kind of a pain, I know. What I do is stick a siphon hose into the reservoir and drain it out into another container, and properly dispose of it along with my other lubes. Then refill the reservoir, run the engine, and turn the wheels left to right to circulate the fluid, bring it back up to temperature, and then siphon it out again and refill. This double cycle allows you to also clean out the fluid in the steering box. The hotter the fluid, the better, as this helps assure that any crud is being carried in suspension. Be sure to check the fluid level several times until you're sure the level has stabilized.
Number two is to use a quality power-steering fluid. Sure, you can use ATF, and maybe it will work just fine. But ATF has friction modifiers specifically designed to work with the clutch packs and bands that automatic transmissions use. Use the right stuff! Consider a synthetic power-steering fluid as it withstands higher temperatures so much better and lubricates better in cold weather (as I write this, the temperature here in Montana is -17 degrees F). Several performance power-steering rebuilders who I have spoken with recommend GM-brand fluid, saying it's the best on the market.
Number three is to get serious about installing a power-steering cooler. It's not that hard to cut into a return line (yes, I said "return line," not the pressure-side line) and extend the line over to a small oil cooler.
One year at Moab on the Hell's Revenge trail, I damaged my power-steering cooler and had to bypass it. While waiting to tackle an obstacle, I happened out of curiosity to put my hand on my steering box and very quickly removed it. Pouring some water over the box made little dancing balls. Yep, it sure was hot. It wasn't too long after that the selector shaft seal failed.
Here is a little test you can do that I call the "paper blotter test": place a drop of power-steering fluid on a paper towel. Usable fluid should disperse and be red or light brown. If it's dark and does not spread out, it's oxidized, and definitely should be changed.
