Which specific benefits do I get when I change oil vs. don’t change

Transmission oil is not eternal. The marketing term lifetime means that the transmission oil is for a lifetime, not eternal. Unfortunately, its lifetime is not defined anywhere and the car manufacturer is guided on the age of the first user.

Transmission manufacturers recommend replacing the oil every 80,000 to 120,000 km (exceptionally, CVT transmission every 40,000 to 60,000 km). If the transmission oil cannot be changed, the lifetime of the transmission, depending on the driving style and gear type, could be 200,000 to 300,000 km.

Typically, this distance will cause serious wear and tear, which in some cases will even require the purchase of a new used transmission (repair is too expensive). Very many used cars that are brought from Western Europe to Estonia are with changed odometer and the actual mileage is significantly higher.

If oil is not changed in the transmission, the oil characteristics change. Because of the heat, the molecules of the oil are shorter, the impurities lose their performance over time, and the concentration of the abrasive particles is increasing.

As the characteristics of the oil have changed, this is particularly evident in two respects: first, gear shifting and hydraulic coupling work are not as good as with oil (knives, jerks, tremors, swing fluctuations in gear shifting and with smooth driving), and secondly, increased wear on transmission components.

What exactly will wear in the transmission? For this, the clutch discs (about 30 to 50 pcs in the transmission), the control surfaces of the gaskets, the bearings and most importantly, the highly processed hydraulic block. The latter controls the operation of the entire transmission.

As a result of heavy wear, the transmission can literally be cut off (burned clutch discs), break down (broken bearings) or irreversibly wear out (hydraulic block). It is not a question of WHETHER these symptoms will come, but WHEN this will happen.

If you do not change the transmission oil, you will keep the oil change price – as a rule, 150-450 € and you will act against the transmission manufacturer’s recommendation. The cost of a complete repair of the automatic transmission is usually between 1500 and 4500 €. There are also few cases where repairs can no longer be carried out because vital parts are broken.

By changing the transmission oil, you significantly extend the lifetime of the transmission. With regular maintenance of the transmission most transmissions do not require repairs.

The following example is about Mercedes 7-speed transmission when it is assumed that the transmission will break over distance of 300,000 km.