BMW E31, E32 and E38 ZF Gearboxes - Should the oil and filter be changed?

This is a question that gets asked all the time - so here is the official statement from ZF Transmissions:

ZF UK Ltd . Abbeyfield Road . Lenton . Nottingham . NG7 2SX

0333 240 1123 . Fax: 0844 257 0666 . www.zf.com/uk

IMPORTANT PRODUCT INFORMATION

ZF AUTOMATIC CAR TRANSMISSIONS

The case for oil servicing and the use of approved oil and filters

The oil is supposed to be lifetime fill – why change it?

1. The oil in a modern automatic transmission is a highly engineered component as it serves
many functions including lubrication, cooling, hydraulic application of clutches and power
transmission via the torque converter.

2. Modern transmissions utilise overlapping application of clutch packs at gear changes (instead
of freewheels) and controlled slip of the torque converter lock up clutch which puts greater
stresses on the oil.

3. To meet these challenges partially synthetic oils have been developed for ZF 5, 6 and 8 speed
transmissions which are maintenance free under normal operating conditions. However, as
some degradation of the oil inevitably occurs over time and usage, ZF recommends oil and filter
changes after 50,000 to 75,000 miles to ensure optimum performance.
4. Oil degradation can lead to complaints such as judder, noises and a deterioration in gear change
quality.

5. Some car manufacturers already recommend oil servicing at 60,000 miles and others are starting
to put greater emphasis on the technical benefits rather than ‘cost of ownership’.

Why use approved oil?

1. There were many approved oils for the simpler 3 and 4 speed transmissions, however it is only
feasible to exhaustively develop and test one oil to meet all the demands imposed on a modern
transmission.

2. Claims are made that alternative oils are equivalent but whilst they might have the same basic
characteristics such as viscosity they won’t have the same crucial additive packages which are
closely guarded secrets of the oil companies.

3. The consequences of using unapproved oils might not be immediately apparent but there are
well-documented cases of problems such as judder and noises occurring after thousands of
miles in service.

A correctly operating filter ensures that potentially damaging particles are taken out of
circulation thereby optimising the transmission operating conditions and extending life.

Why use approved filters?
1. Filtration is a science in itself. Too little can lead to significantly sized particles circulating the
transmission causing wear and risking the seizure of finely toleranced parts e.g. pistons in the
bores of the mechatronic unit. Too much filtration can lead to vital additives being extracted
from the oil and also blockage of the filter.

2. An approved filter ensures correct sealing. This cannot be guaranteed with non-genuine parts
allowing the possibility of unfiltered oil to circulate the transmission giving the associated risks
of failure and premature wear.