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What do transmission oil do?
The main function of the oil used in manual gearboxes, transfer cases and differentials is to lubricate the moving parts of these mechanisms. It protects the contacting elements from abrasive wear and scuffing. Thanks to lubrication, the parts slide more smoothly, which contributes to the fuel efficiency of the vehicle. In addition, the oil removes heat and wear products from friction couples, while the oil film formed on the surface of the components prevents corrosion.
Transmission oil serves the same functions in automatic transmissions, and is also used to transmit torque from the engine flywheel to the gearbox shafts.
How do I know when it's time to change the transmission oil?
It is recommended that the gear oil in manual gearboxes be changed on average every 90,000 to 100,000 km. The oil of semi-automatic gearboxes has a shorter lifespan – approximately 50,000 to 60,000 km. If the car is used in harsh conditions, for example off-road, you may need to change it more frequently. In any case, the replacement interval is regulated by the manufacturer and is specified in the owner’s manual. In an automatic transmission, jerking when shifting gears may indicate that the transmission oil has to be replaced.
What happens if I don’t change the transmission oil?
Over time, the transmission oil oxidizes, which adversely affects its lubricating and anti-corrosion properties. In addition, it becomes contaminated with metal chips that act as an abradant and accelerate the wear of parts. Frequent wheelspin can cause carbon deposits to accumulate in it. All this leads to rapid wear of the transmission elements, reduces the fuel efficiency of the vehicle and the ease of gear shifting.
What is the colour of transmission oil?
New transmission oil is often red, yellow or orange. But during operation it may become dark red or brown. Darkening of the transmission oil does not always indicate its poor condition. If it is clear, without a distinctive smell of burning, and has no visible contaminants and impurities, it still can be used. And vice versa, a turbid dark oil with a strong smell of burning and visible mechanical impurities means that the oil should be replaced immediately, as well as indicates malfunctions in the gearbox.
What are the symptoms of low transmission oil?
Jerks in gear shifting, a smell of burning, gear slipping (slipping of transmission friction elements), foreign sounds, as well as delayed or spontaneous gear shifting can indicate the low level of transmission oil in automatic transmissions. In rear-wheel-drive vehicles, when driving uphill or accelerating, air may get inside the oil lines. As a result, oil pressure reduces, the connection with the engine breaks, and the vehicle slows down. The insufficient oil level may even cause the motor to stall. In some cases the engine continues its operation, however the car is not moving.
Low oil level in manual gearboxes results in cracks, jerks and vibrations during gear shifting.
Check the oil level to make sure the problem is caused by the low transmission oil. Cars with automatic transmissions are usually equipped with a dipstick for this purpose. On some vehicles you’ll have to unscrew a filler plug in the transmission oil pan. The filler plug in cars with manual gearboxes can be mounted behind the front left wheel. See your car owner's manual for more detailed instructions on checking the oil level in your car.
Is it difficult to replace transmission oil?
Yes, this procedure is rather laborious and in most cases requires the use of special equipment. In addition, the gearbox should be flushed before adding fresh transmission oil in order to remove carbon deposits, residues, and wear products of contacting elements. Special additives are used for this.
The duration of this procedure depends on the type of oil change: it can be partial or full. The former implies draining of only some amount of oil. The work takes about 1 hour and does not require special devices. However, the partial change is less efficient. Full oil change requires special equipment and takes about 3 hours.