Dex Iii Power Steering Fluid

Let's talk about DEX III power steering fluid. It’s a fluid many of us have encountered, especially if you’re wrenching on older vehicles. While newer vehicles are increasingly using specialized fluids like ATF+4 or even electric power steering, DEX III (also often written as Dexron III) held a prominent place for many years. This article will delve into the properties, applications, and important considerations when dealing with this specific type of power steering fluid.

What Exactly Is DEX III Power Steering Fluid?

DEX III wasn't just a specific brand; it was a specification created by General Motors (GM). It originally referred to a type of automatic transmission fluid (ATF), but its characteristics made it suitable for use in many power steering systems as well. While technically obsolete – GM superseded DEX III with DEX VI – it's still widely available and used, particularly in older vehicles and systems where backward compatibility is a primary concern. Many aftermarket fluids are labeled "DEX/Merc," indicating they meet the specifications of both GM's Dexron and Ford's Mercon ATF standards.

To understand why it was so popular, let's break down the key properties that made DEX III suitable for power steering systems:

Key Properties and Characteristics

Viscosity: Viscosity is the measurement of a fluid's resistance to flow. DEX III has a viscosity index designed to provide adequate lubrication across a range of operating temperatures. Too thick, and you'll experience sluggish steering, especially in cold weather. Too thin, and you risk insufficient lubrication and increased wear. The targeted viscosity of DEX III was a good compromise for many applications.
Friction Modifiers: These additives are designed to control friction between moving parts. In automatic transmissions, they're crucial for smooth shifting. While power steering systems don’t require the same level of friction control as transmissions, these modifiers still contribute to smooth and quiet operation of the power steering pump.
Anti-Wear Additives: These additives are crucial for protecting the internal components of the power steering pump, rack, and pinion. They form a protective layer on metal surfaces, reducing friction and wear, especially under high loads and pressures. Zinc dialkyldithiophosphate (ZDDP) is a common example, although its use is increasingly limited in newer fluids for environmental reasons.
Oxidation Inhibitors: Power steering fluid is constantly exposed to heat and oxygen, which can cause it to break down and form sludge. Oxidation inhibitors prevent this process, extending the life of the fluid and the system.
Seal Swell Additives: Power steering systems use various rubber seals to prevent leaks. Over time, these seals can shrink or harden, leading to leaks. Seal swell additives help to keep the seals pliable and prevent them from shrinking, maintaining a good seal.
Foam Inhibitors: Air bubbles in the fluid can reduce its lubricating properties and cause cavitation (the formation of vapor bubbles that can damage the pump). Foam inhibitors prevent the formation of air bubbles, ensuring proper lubrication and pump performance.
Corrosion Inhibitors: These additives protect metal components from rust and corrosion, especially in humid environments. They neutralize acids that can form in the fluid and prevent them from attacking metal surfaces.

DEX III in Power Steering Systems: Why It Worked

The combination of these properties made DEX III a suitable choice for many power steering systems. It provided adequate lubrication, protected against wear, and helped to maintain seal integrity. However, it's important to understand its limitations and potential issues.

Here's a breakdown of why it was often selected:

Availability and Cost: DEX III was widely available and relatively inexpensive, making it a cost-effective option for many vehicles.
Backward Compatibility: In many cases, DEX III was backward compatible with older power steering systems that originally used Dexron II or even Dexron. This made it a convenient choice for topping off or flushing systems.
Acceptable Performance: For many older vehicles, DEX III provided acceptable performance in the power steering system. It met the basic requirements for lubrication, wear protection, and seal compatibility.

Potential Problems and Considerations

Despite its widespread use, DEX III isn't a universal solution. There are several potential problems and considerations to keep in mind:

Obsolete Specification: As mentioned earlier, DEX III is technically an obsolete specification. This means that manufacturers are no longer required to meet the original DEX III standards. While many aftermarket fluids are labeled "DEX/Merc," their actual performance may vary. Always choose a reputable brand.
Shear Stability: Over time, DEX III fluid can lose its viscosity due to shear, which is the breakdown of the long-chain polymer molecules that contribute to its viscosity. This can lead to reduced lubrication and increased wear. Regular fluid changes are essential to mitigate this problem.
Not Suitable for All Systems: Crucially, DEX III is not suitable for all power steering systems. Modern vehicles, particularly those with electric power steering (EPS) or specific hydraulic power steering systems designed for lighter, more synthetic fluids like ATF+4 or Pentosin, require fluids with different properties. Using DEX III in these systems can lead to damage and premature failure.
Moisture Absorption: DEX III can absorb moisture over time, which can lead to corrosion and reduced lubricating properties. This is another reason why regular fluid changes are important.
Mixing Fluids: Mixing different types of power steering fluid is generally not recommended. Different fluids may have incompatible additives that can react with each other, forming sludge or compromising the performance of the system. If you're unsure what type of fluid is currently in your system, it's best to flush the entire system and replace it with the correct fluid.

How to Determine if DEX III is Right for Your Vehicle

The most important thing is to consult your vehicle's owner's manual. The manufacturer's recommendation is the definitive source for the correct type of power steering fluid. If your vehicle originally specified Dexron II or Dexron III, a quality "DEX/Merc" aftermarket fluid is often a safe choice. However, if your vehicle specifies a different fluid, such as ATF+4, Pentosin CHF 11S, or a specific power steering fluid, do not use DEX III.

Here are some general guidelines:

Older Vehicles (pre-2000s): DEX III or a DEX/Merc equivalent is often suitable for older vehicles that originally specified Dexron II or Dexron III.
GM Vehicles (1990s-2000s): Many GM vehicles from this era used DEX III in their power steering systems.
Ford Vehicles (1980s-1990s): Many Ford vehicles from this era used Mercon ATF, which is compatible with DEX/Merc fluids.
Vehicles with Electric Power Steering (EPS): Never use DEX III in vehicles with EPS systems. These systems typically require specialized fluids.
Vehicles with Hydrostatic Power Steering: Some vehicles, particularly heavy-duty trucks and machinery, use hydrostatic power steering systems that require specific hydraulic fluids. DEX III is generally not suitable for these systems.

Flushing and Changing Power Steering Fluid

Regularly flushing and changing your power steering fluid is a crucial maintenance task. Here's a general overview of the process:

Identify the Correct Fluid: As emphasized earlier, use the fluid specified in your vehicle's owner's manual.
Locate the Power Steering Reservoir: The reservoir is typically a small plastic container with a cap labeled "Power Steering Fluid."
Siphon Out the Old Fluid: Use a turkey baster or a fluid extractor to remove as much of the old fluid from the reservoir as possible.
Refill with New Fluid: Fill the reservoir with the new fluid to the "MAX" line.
Turn the Steering Wheel: With the engine running, slowly turn the steering wheel from lock to lock several times. This will circulate the new fluid through the system.
Check and Adjust Fluid Level: Check the fluid level again and add more fluid as needed to maintain the correct level.
Repeat if Necessary: For a more thorough flush, you can repeat steps 3-6 several times.

For a complete flush, you can disconnect the return line from the power steering pump and route it into a container. Then, while adding new fluid to the reservoir, run the engine and turn the steering wheel to pump out the old fluid. Be careful not to let the reservoir run dry, as this can damage the pump.

Conclusion

DEX III power steering fluid served its purpose for many years, and it's still a viable option for older vehicles that originally specified it. However, it's essential to understand its limitations and ensure that it's the correct fluid for your specific vehicle. Always consult your owner's manual and use a quality fluid from a reputable brand. Regular fluid changes will help to keep your power steering system operating smoothly and reliably.