Summer School of Hard Knocks

Most motorists are uneducated about automatic transmission fluid. And summer’s the time they learn about this vital fluid the hard way because heat’s one of its biggest enemies. AMSOIL Synthetic Automatic Transmission Fluid can save you the hard lesson with one cool solution.

“Heat and a lack of lubrication are the biggest reasons for shortened transmission life,” according to a study group of transmission technicians commissioned by a major lubricant additive manufacturer.

What makes automatic transmissions hot? Hot weather, city driving, trailer towing, driving steep grades … just about everything a vehicle is exposed to in the summer.

Even vehicle design makes transmissions run hot. Aerodynamic contouring deflects cooling air away from the transmission. Hot-running, low-emission engines keep coolant temperatures high, which in turn, keeps transmission temperatures high. How does the automatic transmission fluid (ATF) fit in?

Responsible for transferring power from the engine to the drivetrain, acting as a hydraulic fluid in the valve body, lubricating gears and bushings and carrying heat away from clutch interfaces, the automatic transmission fluid (ATF) is highly vulnerable to heat damage.


Heat, a form of energy, can break chemical bonds and turn one chemical into another. For example, heat breaks the long chain ATF molecules into short chain sludge and varnish precursors.

Heat also excites molecules so they leave the liquid phase and enter the vapor phase, a process commonly known as boiling. As ATF loses molecules to boil-off (volatility), its volume is reduced and the fluid is thickened.


Oxidation, a chemical process, is hastened by heat. The type of oxidation that occurs in the transmission literally adds oxygen to molecules. Adding oxygen to some molecules forms solids. Adding it to others forms acids. Adding it to short-chain hydrocarbons from heat-damaged ATF forms sludge and varnish.


The solid particles produced by oxidation may settle in passageways and block the flow of ATF, leaving components unlubricated.

Plus, fluid thickened by boil-off and oxidation flows sluggishly, which contributes to poor lubrication and to poor fuel economy as fluid drag consumes power.

ATF dispersant and anti-oxidant additives help ensure adequate lubrication by suspending solids and inhibiting fluid thickening.


The acids created by oxidation may corrode metal components, particularly those containing copper, such as clutches and bushings.

ATF detergent-alkalinity additives work to prevent corrosion by neutralizing acids.

One of the most common – and most treatable – causes of automatic transmission failure is “poor maintenance where the ATF has degraded to the point where it cannot do its job,” according to the transmission technician study group. The easiest – and best – preventive maintenance is a fluid change. And the best replacement ATF, of course, is AMSOIL Synthetic ATF.


Conventional petroleum-based ATF is susceptible to oxidation in several ways synthetic ATF is not. For example, some conventional fluid molecules contain sulfur or nitrogen. These oxygen “magnets” oxidize readily in normal transmission operating temperatures.

Conventional fluids also contain double-bonded carbon atoms which break easily at temperatures commonly
found in hard-working transmissions. Broken chains provide “parking spaces” for oxygen atoms.

Finally, conventional fluids contain long straight carbon chains which, like a long skinny stick, are easy to break. Heat breaks these long chains – creating more room for oxygen atoms.


When Ford and General Motors recently updated their ATF specifications, they tightened the oxidation limits. Each automaker now allows less increase in acid and particle buildup and fluid thickening than they previously did, due to the increased heat challenge automatic transmissions face in new car designs. Each protocol evaluates the oxidative changes undergone by fresh ATF samples in hot, oxidizing test conditions for 300 hours duration.

The GM and Ford tests are designed to test conventional ATF. In so doing, they highlight the superior performance of synthetics. After 900 hours service in the Ford and General Motor tests, AMSOIL Syn-thetic ATF stays in spec. How does AMSOIL Synthetic ATF deliver triple the performance?

  • Contaminantfree synthetic base stocks contain no nitrogen or sulfur to attract oxygen.
  • No double bonds. Synthetic lubricant molecules are fully hydrogenated – there’s no room for oxygen atoms.
  • Strong molecular bonds resist heat damage. Synthetic lubricant molecules are highly branched, not long and thin like conventional lubricant molecules. Just like a stout branched stick is harder to break than a long thin stick, so are highly branched molecules harder to break than long thin ones. Again, no room for oxygen
  • Additives. Quality’s the name of the game. The additive chemistry in AMSOIL Synthetic ATF has been laboratory and road-test proven to provide more than five times the oxidation protection of conventional packages.


Transmission technicians call changing the ATF ‘cheap insurance’ against costly transmission repair. Yet while
the average transmission repair costs $1000 and many motorists would rather sell their car than fix the transmission, most can’t tell you the drain interval for their ATF. They need education, and fast, before they learn about transmission repairs at the summer school of hard knocks, located somewhere on the road to a spoiled vacation.


The automatic transmission isn’t the only place ATF is used. According to some marketers, up to 50 percent of
the ATF manufactured in North America is used in construction, sawmills and logging. ATF is used in hydraulic units and rotary screw compressors, due to its greater thermal and oxidative stability as compared to hydraulic fluid and compressor oil.

Like their automotive counter-parts, these applications cry out for extra protection in the summer, when temperatures and workloads are at their highest.

*All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for the use in the application shown.

SLS Notes:

Keep in mind that the above article was published in June 1996. Transmissions and fluids have changed considerably since then. Newer transmission designs create even more severe requirements for transmission fluids. Add to that the fact that some manufacturers now make it more difficult to change transmission fluids. No easily accessible “Transmission Dip Stick / Fill Tube” and the manufacturers claim the transmission fluids are “Filled-For-Life” fluids that don’t require changing.

If you believe that, read this AMSOIL Tech Tip article asking “What Does Filled For Life Really Mean?” Then check out this Field Test of AMSOIL Lubricants in a fleet of Las Vegas Taxis.

Most independent mechanics now recommend a transmission fluid change at 30,000 to 50,000 miles. I personally know of one transmission with a recommended fluid change at 105,000 miles that failed before 70,000 miles. The owner traded it in and purchased a new car. What would have been better financially? Change the fluid at 50,000 miles or less for $300 or less, $2500+ for a rebuilt transmission, purchase a new vehicle?

Want more information on specific AMSOIL Transmission Fluids? Check This Page.

Not sure which fluid you need? The AMSOIL Lookup can provide that information.

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