Power steering fluid provides hydraulic assist for the power steering system. Most fluids are either mineral-oil or synthetic oil of some type blended with additives to suppress foaming, prevent corrosion and improve lubrication in the power steering pump and steering gear.
Hydraulic power steering systems were used on many vehicles up until the mid-2000s when electric power steering began to replace hydraulic systems. If your vehicle has a hydraulic power steering system, it is important to maintain the fluid and check the level regularly.
HOW TO CHECK POWER STEERING FLUID LEVEL
First you have to locate the power steering pump and fluid reservoir on your engine. The pump is usually belt driven and located on one side of the engine, with the reservoir mounted on top the pump. On some applications, a remote fluid reservoir is used because there isn't room to mount it on the pump. A remote reservoir is often mounted on the inner fender.
If you can't find the power steering fluid reservoir, refer to your vehicle owners manual for its location.
Check the fluid level with the engine OFF.
Filler Cap for PS fluid reservoir.
Wipe any dirt or grease away from the top of the fluid reservoir, then unscrew the cap. The cap may have a dipstick on the underside, or there may be markings on the inside or outside of the reservoir to indicate the FULL level and/or ADD/LOW level.
If the level is low, add the specified power steering fluid to bring the level up to the full mark.
Fluid expands slightly as it heats up, so there may be FULL markings for HOT or COLD on the dipstick. If it's a really hot day and/or the engine is warm, use the HOT FULL mark. If it's a cold day or the vehicle has not been driven for several hours, use the COLD FULL mark.
Avoid overfilling the reservoir as this could force fluid to leak out of the reservoir if there is insufficient head space when the fluid gets hot.
Normally, the fluid level should remain constant for many years of service. But as a vehicle ages, leaks may develop causing a slow loss of fluid. If the level gets too low, air can be drawn into the pump, causing noise and/or a reduction in power steering assist.
HOW TO CHECK THE CONDITION OF THE POWER STEERING FLUID
The color of new power steering fluid will vary depending on the dyes in the product. The fluid may be clear, amber, pink or red. If a normally clear or pink PS fluid has turned dark brown and/or has a burned smell, it is oxidized and needs to be replaced.
If the fluid appears foamy, it is aerated. This may be the result of the fluid level getting too low and pulling air into the pump, or it could be the result of a leaky shaft seal that is allowing air to be mixed with the fluid. Foamy fluid can affect power steering assist but has no effect on the condition of the fluid.
Checking for trace metals in the fluid: Another method for checking the condition of the fluid as well as condition of the entire power steering system is to use a chemical test strip (such as those available from Acustrip). When the test strip is dipped into the fluid, it changes color to indicate the presence of metal wear particles in the fluid. Elevated levels of certain metals such as copper, iron and nickel in the fluid indicate corrosion and/or wear, and the need for a PS fluid change.
POWER STEERING FLUID TYPES
Different vehicle applications may require different types of power steering fluid. Some use ATF transmission fluid such as Dexron, Mercon, Type F, ATF+4, etc.) but many newer vehicles use some type of synthetic-based hydraulic fluid that is specifically formulated for power steering use. Synthetic fluids flow well at low temperature, which improves pump lubrication and longevity.
Although a "universal" power steering fluid may be satisfactory for many applications, some vehicles do require special additives for seal and pump lubricity, and corrosion protection. A top-off fluid must also be chemically compatible with the PS fluid that is already in the system, and the viscosity of the fluid should meet the requirements of the vehicle manufacturer for proper pump lubrication, power steering feel and assist.
European and Japanese vehicles often have their own unique requirements for power steering fluid. Such applications may require a high performance synthetic-based PS fluid that meets DIN 51 524T3 and ISO 7308 standards. Audi, BMW, Mercedes, Porsche, Volkswagen and Volvo all have various power steering fluid requirements which can vary depending on the year/make/model. Many of these applications specify one of several different types of Pentosin power steering fluid. Japanese auto makers such as Honda, Mitsubishi, Nissan, Subaru and Toyota also have their own PS fluid specifications.
The type of power steering fluid that is specified for your vehicle should be marked on the PS reservoir or filler cap. You can also find the recommended PS fluid listed in your vehicle owners manual.
Use the type of fluid specified (or one that meets the OEM requirements) to reduce the risk of incompatibility issues and problems down the road. Using the wrong type of PS fluid is a common cause of power steering pump failure!
Best Advice: If you don't know what type of PS fluid you should use, do NOT add any fluid to the pump reservoir until you can find out the proper type.
POWER STEERING FLUID APPLICATIONS
For a detailed application chart of power steering fluid recommendations by vehicle manufacturer, Click Here.
The following are some general guidelines on power steering fluids (always refer to your vehicle owners manual or the OEM service literature for specifics):
Mineral-oil based universal power steering fluids are usually suitable for any of the following: Applications that specify Dexron, Dexron III, Ford Mercon, Ford M2c-138CJ or Type A ATF fluids. This includes most domestic makes (Chrysler, Ford & General Motors) from the 1970s through 1990s, and U.S.-built VW models from 1984 to 1989.
Mineral-based universal power steering fluids are usually NOT recommended for applications where special fluids are required such as most 1990 and newer European and Japanese PS systems. Most of these require some type of synthetic-based power steering fluid.
Synthetic-based universal power steering fluids are usually suitable for applications that have the following OEM specifications:
American Motor Corporation C 4124
BMW 82 11 0 148 132; 83 29 0 429 576; 81 22 1 468 879 & 82 11 1 468 041
Chrysler MS-1872; MS-5931 & MS-9602
Ford M2C138-CJ; ESW-M2C128-C&D; M2C195-A; M2C204-A & M2C33-F
GM/Saginaw PSF 9985010; 9985835 & 89021184
Hyundai/Kia PSF-3; PSF-4 & PSF 00232-19017
Mercedes Benz 236.3; 345.0; 001 989 24 03 10; 001 989 24 03 12 & Q 1 32 0001
Mitsubishi Diamond SP III & PS Fluid
Navistar TMS 6810
Porsche 000 043 206 56
Saab 93160548; (45) 30 09 800 & 30 32 380
Toyota PSF Type EH; P/N 008886-01
Volvo 1161529 & 30741424
VW/Audi TL-52146; G002000; G 004 000 M2; G 004 000 M7 & G 004 000 M8
POWER STEERING FLUID SERVICE INTERVALS
Power steering fluid operates in a relatively clean environment so it lasts a long time. Most vehicle manufacturers do not even have a recommended service interval for power steering fluid. Even so, after many miles and years of service, wear particles in the steering pump and steering gear can contaminate the fluid. Corrosion inhibitors can also deplete over time, and high underhood temperatures can cause the fluid to oxidize and break down.
Replacing the fluid every 5 years or 50,000 miles can help prolong the life of the power steering system and reduce the risk of expensive repairs down the road.
POWER STEERING FLUSH
Some repair facilities recommend a power steering fluid flush for preventive maintenance. The old fluid is flushed out of the power steering system and replaced with new fluid. The fluid should be flushed regardless of time or mileage is it is dirty or has been accidentally contaminated with any other fluids (coolant, motor oil, brake fluid, etc.).
Flushing is mostly beneficial to newer vehicles with vane-style power steering pumps. These pumps have much tighter tolerances than older roller-style pumps, and can't tolerate contaminants in the fluid.
The power steering system should also be flushed if major repairs are being made, such as replacing the power steering pump, hoses or the steering rack or steering gear. Contaminants in the old fluid can damage new parts, and many power steering component suppliers say you must change the fluid if you want to maintain the warranty on your newly installed parts.
HOW TO CHANGE POWER STEERING FLUID
The easiest way to change the fluid is to disconnect the hoses from the steering gear or rack, and drain the fluid from the power steering reservoir and pump into a container.
This still leaves some of the old fluid inside the power steering gear or rack. The trapped fluid can be removed as follows:
1. Reconnect the pressure and return hoses to the rack.
2. Disconnect the return hose at the reservoir, and temporarily plug the return hose opening in the reservoir so fluid can't leak out.
3. Add fresh power steering fluid to the reservoir.
4. Start the engine and allow the pump to push the fresh fluid through the steering gear and rack and out the return hose. Catch the discharged fluid from the return hose in a container.
CAUTION: Keep a watchful eye on the fluid level in the reservoir and do NOT let the fluid level get too low. Starving the pump while it is running could damage the pump.
An alternative method would be to disable the ignition system and simply crank the engine rather than starting it up. Cranking the engine will drive the PS pump and push fluid through the system. Do NOT crank he engine for more than 30 seconds at a time otherwise you could overheat and damage the starter. Crank for 30 seconds, then wait a minute or so before cranking again. A couple of cycles should do it. Don't overdo it or you will run your battery down.
5. Cycle the steering wheel back and forth several times while the pump is turning and you are flushing the system to make sure the old fluid inside the steering gear or rack has been displaced by fresh fluid.
6. When you have finished flushing the system, shut the engine off, reconnect the return hose to the reservoir and add more PS fluid as needed to bring it up to the full level.
NOTE: If you are replacing the steering gear or rack, there's no need to flush the steering gear or rack. The old fluid inside the steering gear or rack will go bye bye along with the old parts. But if you are replacing a pump or hoses, you should flush the system using the just described procedure to remove the old fluid and contaminants.
GETTING TRAPPED AIR OUT OF A NEW STEERING RACK
If you are replacing a power steering rack, air may become trapped inside the rack power cylinder. To remove the air, slowly cycle the steering wheel lock-to-lock 6 to 10 times without hitting the stops while the engine is idling. This should help force any air trapped in the power cylinder out of the rack. Do this with the front end of the vehicle raised and supported on jack stands so the wheels are off the ground and can be steered side-to-side with minimum effort. Repeat this procedure as needed until the steering is quiet and feels smooth.
Also, it may help to let the vehicle sit for 30 minutes or so after the initial filling before performing this bleeding procedure.
On some applications, it may be necessary to use a hand-vacuum pump to evacuate air from the system. Vacuum is applied to the fluid reservoir to draw air out of the system.
POWER STEERING FLUID FILTERS
A small screen filter may be located in the return line where the hose connects to the PS reservoir. The filter may contain a magnet to help trap metallic wear debris in the system. If this filter becomes clogged, it can obstruct the flow of fluid in the system.
Replacing the filter is recommended when changing/flushing the power steering fluid or when replacing a pump, steering gear or rack.
An aftermarket inline filter may also be installed in the return line to provide added protection if the original system has no filter.
POWER STEERING FLUID LEAKS
The most common problem with hydraulic power steering systems is fluid leaks. Power steering fluid can leak from hoses and hose connections, from the power steering pump or from the power steering gear or steering rack. The ends seals on a power steering rack as well as the O-ring seals in the spool valve assembly are where fluid leaks often occur.
Power steering fluid is usually colorless (clear), but it may be pink or red if the system uses ATF Fluid. Telltale spots on a garage floor or driveway, and/or a drop in the fluid level in the power steering pump reservoir are clues that the system is leaking fluid.
If the fluid level gets too low, the pump may become noisy or you may feel a loss of steering assist as air is drawn into the system. Hydraulic fluid is incompressible and a hydraulic system needs an incompressible fluid to transfer pressure from the pump to the steering gear. Consequently, if air gets into the system, it will cause a drop in pressure and loss of power steering assist.
POWER STEERING FLUID ADDITIVES
Aftermarket power steering additives are available that can slow or temporarily plug a fluid leak. The seal conditioners in these products can help swell aging seals to slow the loss of power steering fluid. But such additives are not a long-lasting or permanent fix for your problem. You need to replace the leaky parts.
Aftermarket power steering fluid additives also contain friction modifiers that can help quiet noisy pumps. But again its a temporary band-aid that does not fix the underlying problem. If your power steering system is noisy, there is air in the system or the pump or control valve is worn and needs to be replaced.
More Power Steering Articles:Troubleshooting Rack & Pinion Steering
Variable-Assist Power Steering Systems
Electric Power Steering
Click Here to See More Carley Automotive Technical Articles