Whether or not to change the oil in the latest ZF Services automatic transmissions is an ongoing cause of confusion among vehicle owners and independent garages alike.
This is hardly surprising – rarely is a transmission oil dipstick seen in the engine compartment these days, and many car manufacturers’ maintenance schedules omit transmission oil change as a service operation. Often described as ‘filled for life’, the transmission and oil are therefore presumed to perform reliably without intervention.
However, the oil is a highly-engineered, multifunctional component in its own right. Aside from lubricating, it also acts as a coolant, enables hydraulic operation of transmission brakes and clutch packs, and transfers power to the remainder of the drivetrain via the torque converter. Regular renewal benefits transmission performance and longevity.
Although ZF’s newer transmissions are simpler in design – the six-speed 6HP26 contains 29% fewer parts than the five-speed 5HP24 that it replaced – demands on the oil have increased. Overlapping application of clutch packs instead of freewheels, and controlled slip of the torque converter lock-up clutch raise operating efficiency and deliver smoother gear changes, but place greater stresses on the oil.
The reliability of a modern automatic transmission depends on original equipment
oils and filters to protect the complex internals.
Choosing the correct oil
Under normal operating conditions, some degradation of the automatic transmission oil occurs with use and age, as friction materials and load bearing surfaces wear and the oil undergoes repeated temperature cycling. This can lead to judder, abnormal noise and deterioration in gear change quality, so ZF recommends carrying out transmission oil and filter changes after 50,000 to 75,000 miles. A range of part-synthetic oils for ZF’s five-, six-and eight-speed automatic transmissions has been developed for this purpose.
Increasingly critical demands on the oil mean that only a single product is now developed, tested and approved for each new range of ZF transmissions. These ZF-branded ‘Lifeguard’ oils are also packaged and marketed under alternative references by various VMs using the transmission.
Reference list TE-ML 11, available at www.zf.com/lubricants, is regularly updated. You should be aware that any oil not on the list has not been tested and approved by ZF.
OE filter benefits
The quality of the automatic transmission oil filter is equally important. Inadequate filtration or poor sealing can lead to particulate contaminants of significant size circulating, which can accelerate wear and increase the risk of seizure for parts operating within close tolerances, such as the pistons in the mechatronic unit. Conversely, over-filtration can lead to vital additives being excluded from circulating with the oil, and blockage of the filter.
Kits can simplify maintenance
For simplicity, all the parts required to carry out an oil change for any ZF five-, six- or eight-speed car automatic transmission are now available from ZF Services UK in an oil change kit.
Popular kit part numbers include 6HP19-21OSK 01 for the 6HP19 and 6HP21 transmissions, and 6HP26-28OSK 01 for the 6HP26 and 6HP28. Oils, filters, sump pans and other spares can also be purchased individually.
ZF oil change kits are available for all ZF 5-, 6-and 8-speed automatic transmissions
