Whether or not to change the oil in the latest automatic transmissions is an ongoing cause of confusion among vehicle owners and independent workshops alike, says Wayne McCluskey, Technical Training Manager at ZF Services. Particularly when described as ‘filled for life’, the transmission and oil are often presumed to perform reliably without intervention. However, improved understanding of the oil’s functions is leading a number of car manufacturers to rethink this position and recommend automatic transmission oil servicing at regular intervals to benefit performance and longevity. Although the details here refer to ZF transmissions, the advice can be viewed as best practice guidelines for any car equipped with an automatic gearbox.
The reliability of a modern automatic transmission depends on original equipment oils and filters to protect the complex internals.
While ZF’s newer transmissions are simpler in design, in terms of number of component parts, technological improvements demand that the oil itself is recognised as a highly engineered, multifunctional component. Aside from lubricating,
it 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. 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 also place greater stresses on the oil.
OIL CHANGE INTERVALS AND CHOOSING THE CORRECT OIL
Under normal operating conditions, automatic transmission oil suffers some degradation with use and age. Friction materials and load bearing surfaces wear and the oil endures repeated temperature cycling, potentially leading to judder, abnormal noise and deterioration in gear change quality. ZF recommends carrying out transmission oil and filter changes after 50,000 to 75,000 miles. Increasingly critical demands on the oil mean that only a single product is developed, tested and approved for each new range of ZF transmissions. The result is a range of ZF-branded ‘Lifeguard’ part-synthetic oils to suit its five, six and eight-speed automatic transmissions. These oils are also packaged and marketed under alternative references by vehicle manufacturers using the transmission. Reference list TE-ML 11, available at www.zf.com/lubricants, is regularly updated – any oil not on the list has not been tested and approved by ZF.
ZF oil change kits are available for all ZF 5, 6 and 8-speed automatic transmissions.
BENEFITS OF ORIGINAL EQUIPMENT FILTERS
The quality of the automatic transmission oil filter is equally important. Inadequate filtration or poor sealing can leave particulate contaminants circulating, which 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.
OIL CHANGE KITS 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. Oils, filters, sump pans and other spares can also be purchased individually.