Frequently asked questions / Transmission oils – Automatic transmissions
What are the key functions of ATF oil?
Given the specificities of automatic transmissions operation, ATF oils have the following functions:
- Power transmission from the engine to the mechanical part of the automatic transmission;
- Lubricating fluid for the friction discs during start/stop;
- A lubricating and working fluid in the automatic transmission hydraulic system;
What additional features do ATF fluids posses compared with manual transmission fluids?
- They operate as a hydraulic medium, lubricant for friction discs, as well as a working fluid in hydraulic clutches (torque converters)
- For the production of ATF, both mineral and synthetic base oils are used mixed in different ratios and with a wide range of functional additives (these products require the largest variety of functional additives).
Frictional characteristics? What does this mean?
The frictional characteristics are that specific requirement distinguishing ATF from other transmission oils. They are determined from the friction coefficient values (static and dynamic) specified in the transmission manufacturer’s specification. The ATF frictional characteristics should remain constant within the prescribed fluid change interval. That is why the ATF fluid in the gearbox should always be topped up or replaced with a properly selected product.
In what other applications is ATF used?
- ATF is also used in most power-assisted steering systems of cars.
- ATF fluids can be used in some manual gearboxes (e.g. some car models of Mercedes-Benz, BMW, Ford, Opel, etc..)
- They are applied in certain industrial hydraulic systems as well.
Is it possible to use plain hydraulic oil instead of ATF in the hydraulic steering system?
The use of hydraulic oil type "MHL" (which is widely available on the market) is not recommendable unless it is specifically indicated.
Topping up with МТF and ATF?
Oils for manual transmissions are compatible with each other, but even with topping up, replacement is still necessary. Always use oil of the same viscosity grade and performance level to top up.
It is wrong to top up with MTF a gearbox that has been filled with ATF!
In automatic transmissions topping up with a random ATF product can also be dangerous.
Changing the transmission oil in manual transmissions. What is the recommendable mileage?
As it is well known, the recommendations for transmission oil quality and change intervals are given by the manufacturer of the transmission, or the car, respectively. The service documentation, therefore, contains recommendations depending on the operating conditions. In summary, mileage-based intervals would be:
- Passenger cars and light commercial vehicles - 60,000 -120,000 km, unless otherwise specified;
- Large goods vehicles - 20,000 to 100,000 km or once a year, unless another time period is specified;
- Excavators, bulldozers, tipper lorries - 1000 - 2000 engine working hours
The suggested operating periods are approximate and can be reached in roadworthy equipment where lubricants are selected according to the equipment manufacturers’ requirements. If the change interval recommended by the manufacturer differs from the range given above, the manufacturer’s recommendation is to be applied.
Changing the automatic transmission oil
Modern cars with automatic transmissions usually have a recommendation for quite an extended fluid change interval – about 80-100 000 km. There are a significant number of cars with transmissions that are maintenance-free and they are known as fill-for-life, meaning that the oil is supposed to last the life of the transmission. In older cars from the late ‘80s and ‘90s, the oil should be changed each 20-40 000 km unless otherwise specified.