Testing and Service Equipment for Transmissions and Transmission Fluid

Frequently Asked Questions About Transmission Oil Changes, Transmission Flushing, Oil Pressure Tests, Oil Condition, and Filling

Transmission problems can stem from mechanical or hydraulic causes, as well as issues with oil condition, oil level, or oil supply. For reliable diagnosis and maintenance, electronic vehicle diagnostics, mechanical measurements, and professional transmission oil service should therefore be combined. Here, we answer common questions about transmission oil changes, transmission flushing, oil pressure testing, oil condition, and oil filling.

• Why is transmission fluid important for the proper functioning of a transmission?

  Depending on the type of transmission, transmission fluid performs several functions.

  These may include:

  • Lubrication of gears and bearings
  • Heat dissipation
  • Hydraulic power transmission
  • Actuation of clutches and shifting components
  • Protection against wear and corrosion

  In automatic and dual-clutch transmissions, the fluid is often also a component of hydraulic control and actuation systems.

• Does transmission fluid need to be changed regularly?

  That depends on the vehicle, the transmission, and the oil used.

  There is no universal oil change interval that applies to all transmissions.

  The following factors are decisive:

  • Vehicle manufacturer
  • Transmission manufacturer
  • Transmission type
  • Transmission fluid used
  • Driving and operating conditions
  • Maintenance schedule

  Even for transmissions labeled as “lifetime-filled,” transmission manufacturers may recommend an oil change depending on usage and load.

• What does “lifetime” transmission fluid mean?

  “Lifetime” does not necessarily mean that the oil will retain its original properties indefinitely under all operating conditions.
  
  High temperatures, heavy loads, frequent towing, aggressive driving, or high mileage can affect oil aging.
  
  Therefore, the current service and maintenance guidelines from the respective vehicle or transmission manufacturer are always decisive.

• What is the difference between an automatic transmission fluid change and a transmission flush?

  During a standard oil change, the transmission fluid that drains out through the designated drain port is replaced.

  Depending on the transmission design, some of the used fluid may remain in, for example:

  • the torque converter
  • lines
  • the cooler or heat exchanger
  • the hydraulic system

  .

  During a transmission flush, additional transmission fluid is circulated through the system, and the old fluid is replaced with new fluid.

  Professional automatic transmission flushing machines are available for such tasks.

• Is it a good idea to flush the transmission fluid in every automatic transmission?

  There is no one-size-fits-all answer.

  Whether a transmission can be flushed—or which method should be used—depends on:

  • Transmission type
  • Vehicle manufacturer
  • Transmission manufacturer
  • Condition of the transmission
  • Prescribed service procedure

  Therefore, the relevant manufacturer specifications should be checked before flushing.

• Which transmissions can be serviced using an automatic transmission flushing machine?

  That depends on the device used and the available adapters.

  Leitenberger AGSG flushing units are designed for various types of:

  • converter automatic transmissions
  • continuously variable automatic transmissions
  • dual-clutch transmissions.

  Various vehicle- and transmission-specific adapters are available for connection.

• What is ATF?

  ATF stands for Automatic Transmission Fluid.
  
  These are specially formulated fluids for automatic transmissions.
  
  The requirements vary significantly between different transmissions.
  
  Therefore, only oil that is approved or specified for the specific transmission may be used.

• Can you mix different types of transmission fluid?

  This should not be done without express approval.

  Transmission oils differ, for example, in terms of:

  • Viscosity
  • Additive composition
  • Friction characteristics
  • Material compatibility
  • Approvals

  Using the wrong oil can impair shifting performance and transmission function.

• Why is the transmission oil temperature important during an oil change?

  In many transmissions, the correct oil level depends on the oil temperature.
  
  Transmission oil changes volume with temperature.
  
  For this reason, vehicle and transmission manufacturers often specify a certain temperature range and a defined procedure for checking the oil level.

• How do you set the correct transmission fluid level?

  The procedure varies depending on the transmission.

  Depending on the vehicle, the following steps—among others—may be required:

  • Position the vehicle horizontally
  • Reach the specified transmission oil temperature
  • Let the engine run
  • Shift through all gears
  • Add oil through a designated fill or check port
  • Check the specified oil level

  The manufacturer’s instructions always take precedence.

• Why shouldn't an automatic transmission be overfilled?

  An incorrect oil level can impair the transmission's operation.
  
  Both too little and too much oil can cause problems.
  
  Therefore, the specified fill level and oil level checks must be followed.

• What symptoms might indicate problems with the transmission fluid?

  Possible symptoms may include, for example:

  • delayed shifting
  • shifting jerks
  • jerky movement
  • unusual noises
  • delayed power transmission
  • unusual behavior when the temperature changes

  However, such symptoms do not automatically prove that the transmission fluid is the sole cause.

  The entire transmission should be systematically diagnosed

• Can transmission fluid be tested for contaminants?

  Yes.

  Certain contaminants can be detected using appropriate testing methods.

  Leitenberger, for example, offers transmission oil testers for detecting coolant in transmission oil.

  This can be particularly helpful if an internal leak between the cooling system and the transmission oil circuit is suspected.

• How can coolant get into the transmission fluid?

  In vehicles equipped with a transmission fluid heat exchanger, the transmission fluid and coolant circuits may be located close to each other by design.
  
  An internal leak can cause the fluids to mix.
  
  Even minor contamination can therefore be diagnostically significant if a corresponding fault is suspected.

• How can coolant be detected in transmission fluid?

  The Leitenberger GP 01 or GP 01_BM is used to centrifuge a gear oil sample.
  
  This allows components or contaminants to separate so they can then be visually assessed.
  
  The testing device is specifically designed to detect coolant in gear oil.

• Why is the oil pressure in an automatic transmission measured?

  Many automatic transmissions use a hydraulic oil circuit.

  Transmission oil pressure is important, among other things, for operating various hydraulic components.

  A mechanical pressure measurement can help determine the actual pressure in the transmission oil circuit.

  Oil pressure testers for automatic transmissions are available for this purpose.

• Can a diagnostic device replace mechanical oil pressure measurement?

  Not entirely.

  For example, an electronic diagnostic system can display:

  • error codes
  • sensor readings
  • transmission temperature
  • shift states
  • ECU information.

  Mechanical pressure measurement, on the other hand, shows the actual hydraulic pressure present at the measurement point.

  Both methods can complement each other during troubleshooting.

• How is transmission fluid added after a service?

  That depends on the specific transmission.

  Many modern transmissions do not have a traditional fill port in the engine compartment.

  Transmission fluid must therefore be added through the appropriate service ports using suitable adapters.

  Transmission fluid fill pumps and fill adapters are available for this work.

• Can transmission oil fill pumps also be used with manual transmissions?

  Yes.

  Depending on the model, Leitenberger transmission oil fill pumps are not intended exclusively for automatic transmissions.

  For example, they can also be used to fill:

  • manual transmissions
  • transfer cases
  • differentials.

  The required fill adapter depends on the specific vehicle and powertrain.

• Why are there different transmission fluid fill adapters?

  Filling ports and connections vary by manufacturer and transmission type.

  That is why various adapters are available, for example, for:

  • VW/Audi
  • BMW
  • Mercedes-Benz
  • Ford
  • Toyota
  • Nissan
  • other applications.

  With a quick-connect coupling, the adapters can be quickly changed when used with compatible Leitenberger fill pumps.

• What should you keep in mind when performing a transmission fluid service on hybrid vehicles?

  Hybrid transmissions may contain high-voltage electrical components or be structurally connected to them.
  
  Therefore, additional qualification and safety requirements may apply during certain procedures.
  
  Before performing transmission fluid service, always follow the vehicle- and transmission-specific manufacturer’s specifications.

• What equipment is recommended for a professional transmission fluid service?

  Depending on the workshop services offered, the following may be particularly useful:

  • Automatic transmission flushing machine
  • Transmission fluid tester
  • Oil pressure tester for automatic transmissions
  • Transmission fluid filling pump
  • Matching vehicle-specific filling and flushing adapters
  • Electronic vehicle diagnostics
  • Ability to monitor transmission fluid temperature

  You can find additional solutions under Test and service equipment for transmissions and transmission fluid.