If you've ever come across a Jeep on the trail that has a power-steering pump screaming like a wounded monkey, you know what air in your power-steering system sounds like. It's not too often you have to crack your power-steering system open, but if and when you do, there are ways to ensure you don't wind up with aerated fluid that will cause your pump to whine, scream, and overheat.
We called the gang at PSC Motorsports to get their input on how to properly bleed a power-steering system. The company builds and installs all sorts of killer steering setups -- from stock conversion to hydro assist, to full hydro balanced ram systems -- so the techs there know what they're talking about. Here's what they had to say about keeping your steering system from screaming bloody murder.
The biggest mistake people make when bleeding their power-steering system is to rush things. You're trying to get all the air out of the fluid. It can either be in large pockets or trapped as tiny bubbles in the fluid. Running the engine and turning the wheel with air in the system will tend to aerate and foam the fluid, so you need to give some time for the bubbles to work their way to the top of the reservoir. Here's the PSC's procedure.
1) Jack up the front of the vehicle and suspend the front axle on jackstands so the tires are off the ground.
2) Top off fluid reservoir and briefly start engine for a second or two. Don't turn the steering wheel.
3) Top off fluid.
4) Start engine and cycle steering all the way to full lock one way, then the other. Shut off engine.
5) Let vehicle sit for 5 to 10 minutes for air to leave fluid.
6) Top off fluid.
7) Start engine and cycle steering all the way to full lock one way, then the other five to eight times. Shut off engine.
8) Let vehicle sit for 5 to 10 minutes.
9) Top off fluid.
10) Start engine and cycle steering all the say to full lock one way, then the other. Shut off engine.
11) Remove reservoir cap and check to make sure fluid is clear with no bubbles.
12) Start engine with reservoir cap removed and check to see if fluid is standing still. If air bubbles are present, air is still in system, and repeat steps 8- 12.
Air in a power-steering system will eventually cause the pump to overheat and fail during hard use. PSC cites a few common causes for air in the system, most notably a bad reservoir-to-pump O-ring. Even if your pump doesn't leak when the engine is shut off, if the O-ring is bad then the pump can suck air when it's working. This will eventually cause the pump to whine and overheat. To check the O-ring, either put a source of vacuum to the pump and see if it bleeds down, or submerge the pump in a tank of solvent and pressurize it with 2 to 4 psi of air. If you see bubbles you need to replace the O-ring.
You could also have air in the system and not realize it. One test is to run the engine with the power-steering reservoir cap off. If you shut off the engine and fluid spurts out the reservoir, there's probably an air pocket that's getting compressed while the pump is running. Once the pump stops, the pressure on the air is released and it shoots out the fluid. Follow the bleeding steps to remove it.
Finally, for those running a remote reservoir or power-steering cooler, PSC recommends running no more than 16 inches of 5/8-inch diameter hose to prevent cavitation problems caused when the pump starves for fluid. Make sure your remote reservoir is the highest component in your system. If you're running a power-steering cooler, make sure to mount the cooler lower than the fluid reservoir and that the input to the cooler is on the bottom and the outlet is on the top. That way the fluid can't cascade down when the engine is shut off and cause an air pocket.