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DEXRON 2 Vs 3: What Is The Difference?

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Triax Multi-Purpose ATF DEX III MERC, Synthetic Blend, Friction Optimized, No Slip, Flawless Shifting, -50 F Cold Flow - 1 Gallon

Vehicles manufactured before two thousand five used one of the two options for General Motors: Dexron® II or Dexron® III. Each formula was built on the previous version and acted as an improvement to its predecessor. So, what exactly is the difference between Dexron® II and Dexron® III? Is one better than the other?

The main difference between the two is displayed in the chart below:

 Dexron® IIDexron® III
Released Date1970-19791993
Backward CompatibilityNoYes
Currently AvailableNoNo
Replaced by Dexron® VIYesYes

Chart displaying the difference between the two formulas (DEXRON® III Is an upgrade)

 Knowing the difference between the two formulas can save a lot of time and money in expensive and unnecessary repairs to the vehicle. Dexron® fluids are backward compatible with previous formulas but not forward compatible. Therefore, one must be careful to use the correct formula to prevent irreversible damage to the transmission.

What Does Dexron® Automatic Transmission Fluid Actually Do?

Because the parts inside the transmission are moving “automatically,” the series of solenoids and other hydraulic components that are not present in standard manual transmissions require a fluid other than a thicker oil for the transfer box (Manual transmissions used gear oil instead of Transmission fluid).

The solenoids that help switch the gears use the hydraulic fluid to do two things,

  1. Shift the gears
  2. Aid in Holding the gears in place and lubricating them

While gear oil maintains its viscosity while cold, it changes consistency as it heats up (Hence the rating 75W-80, or 10w-40). Since the oil gets thinner as it heats up, the viscosity of that specific oil is no longer within the range needed for a consistent operation of the appliance, hence the use of Hydraulic fluid.

Carbon-based Hydraulic fluid is made from crude oil and contains the appropriate lubricating properties needed to keep the transmission running smoothly.

The Automatic Transmission is a combination of planetary gear combinations and clutch plates that allow a set of gears to increase or decrease the vehicle’s speed. Depending on the actual transmission, rates, and capabilities, Hydraulic fluid is needed mainly for temperature controls and controlling the pressure inside the transfer case for each of the gears.

Close up of an automobile transmission gearbox lubrication on the gears

My Transmission Doesn’t Have Solenoids To Help Change Gears

Vehicles that use an older transmission design, such as the traditional automatic transmission, may not have direct access to the solenoids that operate, or early models of automatic transmissions may not even have solenoids to aid the transmission in shifting gears.

Although automatic transmissions work with the same components, they may be engineered differently to accommodate the pressure needed to change gears inside the transmission. This hydraulic fluid has the properties required to compensate for the lack of interaction between the vehicle operator and the gear ratios needed to power the car down the road.

Dexron® II Prevents The Components From Wearing Down From Friction

Before the Dexron II formula, the automatic transmission fluid was present mainly to relieve friction in automatic transmissions. The concept of automatic transmissions was still relatively new (less than one hundred years old), so naturally, the hydraulic fluid needed to power these transmission types was also unique.

The other exceptional Properties of Dexron® II are:

  • High-Temperature Oxidation
  • Better Formula for less Air Bubbles
  • Low-Temperature Fluidity

These older transmissions used hydraulic pumps to circulate the fluid inside the automatic transmission. Newer models will use solenoids for the same purpose. The Dexron® II formula provided many solutions for the optimal performance of these vital components of an automatic transmission. Another concern was the temperature of the fluid and its state change of matter.

Dexron® III Provides Improved Friction Resistance Over Dexron® II

Dexron® III is a potent formula that improves the qualities of Dexron® II, which is why it can be used as a backward-compatible fluid. Dexron® III took all the superb qualities that Dexron® II offered at the time and improved them. The differences between the two are just improvements in the features and benefits of the previous formula.

Dexron® III’s Best Qualities are:

  • Longer Protection against Wear over Previous versions
  • Improved Friction over Dynamic Functions
  • Higher temperature Oxidation Stability than previous versions
  • Better anti-foaming properties and low fluidity temperatures

Dexron® III is an improvement on the Dexron® II formula, which was still being used with Hydraulic pumps inside the transmission (Now engineers use solenoids). Following the evolution of lubricants, Dexron® III has given rise to Dexron® VI, an even better formulation of Dexron® III. The two are backward compatible, and one can use Dexron® VI instead of Dexron® II or III.

Valvoline DEX III MERC (ATF) Automatic Transmission Fluid 1 QT.

Valvoline DEX MERC (ATF) Automatic Transmission Fluid 1 QT

Do Dexron® II and III Have Freeze Protection For My Vehicle?

One of the reasons that Manuel transmission used higher-rated gear oil for the transmissions was because of the viscosity levels set forth by the Society of Automotive Engineers (SAE). To sum it up, the higher the first number (the one with the W following it), the temperature at which the oil will maintain its fluidity when cold. The second number is the temperature to which the fluidity starts to become least effective (or break down) when it is warm.

The rating is more than just the temperature rating; the temperature rating is a large part of the calculation for freeze protection. Traditionally, gear oil used in manual transmissions was able to maintain its lower temperature fluidity between twelve below Celsius and fifty-five below, depending on the blend (i.e., 70w, 80w, etc.).

Dexron® II and Dexron® III have low-temperature fluidity levels that maintain their viscosity at a consistent level when cold and warm up to a temperature of negative forty-five degrees Celsius. This means that the hydraulic fluid is the same consistency whether it is negative forty-five degrees outside or forty-five degrees Celsius (this is not an implied scale).

The carbon-based liquid does not reach temperatures inside a vehicle that converts it to a frozen state; instead, the Dexron® liquids (all of them) become too thick for the pumps to push the fluid through the proper components, which makes it useless, but not frozen.

Do I Need To Let My Car Warm Up With Dexron® II, III, or VI?

Automatic transmission fluid does not freeze at average operating temperatures; therefore, there is no need to allow the vehicle to “warm up” before driving the car with Dexron® II or III as far as the transmission is concerned. There are other benefits to allowing the fluids to cycle through the engine before engaging the machine to perform as intended.

Using the Correct Type of Fluid for Your Transmission is Essential to its Performance.

Changing the transmission fluid as the manufacturer recommends is vital for the appliance’s longevity. Using the correct fluid makes all the difference in how the transmission operates. Unfortunately, in older GM vehicles, there are few options available for which fluid to place inside the car. So many changes have occurred over the years to the availability of resources, and it is impossible to find Dexron II or III with current manufacturing practices.

Vehicles That Use Dexron® Transmission Fluids are:

  • Buick
  • Chevy
  • Cadillac
  • GMC
  • Pontiac
  • Oldsmobile
  • Hummer
  • Other brands by Contract through GM Co-Partnership Programs (where GM provided the technology about worldwide brands in total)

The ingredients used in both formulas are the most significant differences between the two fluid types. Dexron® II used more natural lubricating ingredients, while Dexron® III used a combination of synthetic and natural ingredients. These older fluids could also be substituted for power steering lubricants or hydraulic fluids.

It is possible to find similar fluids comparable to the older versions of Dexron® IV®; however, Dexron® IV is also backward compatible with the previous versions of Dexron® transmission fluids.

1970 Oldsmobile Cutlass Convertible yellow near the water on a sunny day with the top open
1970 Oldsmobile Cutlass Convertible

Is Dexron® II and III Still Manufactured and Used Today?

Dexron® II and III formulas are manufactured and sold by third-party lubrication companies for applications not associated with automatic transmissions built after two thousand and five. The application of these fluids is used in generators, power steering boxes, ATF fluid for commercial applications, and gearboxes.

Dexron® II and III are sometimes even used in applications where the power steering fluid needs to be a specific viscosity (mostly in German or European vehicles); the blend often contains a mix of ATF fluids and other components to create the blend needed for optimal performance of the targeted components.

Can I use Dexron® III on pre-1993 vehicles?

The Biggest Differences Between Dexron® II and Dexron® III were the ingredients used to manufacture the two different formulas. The Dexron® III is backward compatible with older GM models; unfortunately, it is not manufactured in twenty and twenty-two. The newer formula of Dexron® VI is currently used in all GM products, including classic vehicles.

Can I Top Off My Dexron® II Vehicle With Dexron® III Or Dexron® IV

Topping off any transmission fluid with a higher version of the Dexron® formula is okay. Although a complete flush and refill are recommended (if proper care for the transmission has been maintained and realized), it is not required to use the newer formulas. However, Backward compatibility does not mean compatibility forward; one cannot put Dexron® II in a vehicle engineered to use Dexron® III.

The reason for this is the viscosity of the fluid and how it interacts with two main components:

  1. The current components of the transmission
  2. The previous detergents and chemicals used in the earlier versions of the formula.

Dexron® IV is backward compatible with mainly all GM products; the question is whether the product manufacturer (i.e., Castrol, STP, Mobile, etc.) creates the Dexron® IV formula with quality ingredients. In addition, Gm no longer holds the formula rights for these fluids, which allows chemical fluid companies to produce their own versions of the formula.

Castrol 03520C TRANSMAX DEX/MERC ATF, 1 Gallon, Automatic Transmission Fluid

Castrol 03520C TRANSMAX DEXMERC ATF, 1 Gallon, Automatic , Black

Can I Mix Mercon® and Dexron® In The GM Transmission?

You absolutely cannot mix Mercon and Dexron® fluids in the transmission unless they are premixed variations of multi-purpose transmission fluid. Several scientific reasons go beyond the scope of this article as to why this is a bad idea. However, the main component of the problem has to do with the consistency of the fluid and how each piece interacts with the fluid mix types.

In Fact, many manufacturers advise against using aftermarket hydraulic fluids because most of these formulas are designed to be compatible with many versions of the engineered design of specific vehicles. For example, mostly all fords will use Mercon, while many GM products use Dexron. In addition, Toyota, Honda, and other manufacturers have their own versions of hydraulic fluid with engineered designs.

Will The Use Of Incorrect Fluid Damage My Car?

The engineer that designed the transmission and other components did so with a specific hydraulic formula blend for that typical arrangement of parts. The amount of pressure needed for the components inside the transmission to work correctly directly results from the fluid type and viscosity of the fluid.

If the fluid falls short of the engineer’s carefully planned operational range requirements for the formula, the vehicle will not perform as required and will suffer long-term damage. Therefore, using the correct fluid type inside the transmission is vital. Not doing so can cause something minor as the vehicle operating sluggishly, or something more pressing such as transmission failure. 

I Have a Continuously Variable Transmission (CVT). Can I Use Dexron® II, III, or IV?

Using the incorrect fluid type in any transmission will damage the car. It is better to consult the owner’s manual for the correct fluid type, weight, and viscosity needed to operate smoothly. A CVT works differently entirely from an automatic transmission and therefore requires the use of CVT hydraulic fluid as a lubricant.

If Running a GM Product, the Car Should be On Dexron® IV

Dexron® II and III are obsolete formulas that are no longer used in modern-day vehicle applications. Some vehicles manufactured pre-2005 may state that they require Dexron® II or III, but Dexron® IV is the current formula for GM automatic transmissions. An automatic transmission requires hydraulic fluid and using the incorrect type will cause long-term damage.

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Valvoline DEX III MERC (ATF) Automatic Transmission Fluid 1 QT.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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