99MercMystLS25 you might want to read this?
Primary Cause of ATX failure
o Insufficiently frequent ATX oil changes & overheating are the primary causes of automatic gearbox failure.
o ATX oil (ATF) should run at 175oF, every 20oF above that halves its lifetime - coolant temperatures quarter its lifetime. The gearbox oil is continually contaminated by the circulation of clutch-pack abrasive particles throughout the gearbox.
o Factory change intervals (600hrs) are too long compared to the high temperature service life (300hrs) of ATX oil.
o In slow moving traffic there is little or no airflow over the tiny factory cooler, and at the same time the thermal input into the ATX oil will be at it's greatest through normal torque-convertor slippage. At a minimum the factory should have implemented a slightly larger cooler with it's own temperature switched fan.
o The CD4E is a poor transmission, the 4EAT/GF4A-EL is a better transmission (fitted to V6s) but both have overheating problems.
Solutions
o Stage-1 - Improve Contaminant Removal
-- Annual ATX fluid changes
The factory specified interval of 2yrs/24,000 miles is too long.
An average speed of 40mph for 24,000 miles requires 600 hours of running, yet ATX gearbox fluid will degrade in GM THOT tests under 300 hours.
Thus the ATX fluid change interval should instead be 1yr/12,000 miles.
A Synthetic ATX fluid is available and withstands higher temperatures, but in view of the abrasive material contamination in ATX gearboxes it is better to use a non-synthetic oil annually than be forced through expense to leave a synthetic oil in for two years: clean oil is best. Clean oil can also markedly improve shifting & fuel economy.
-- Avoid Incomplete ATX fluid changes
Changing the oil on an ATX involves dropping the ATX oil pan and replacing the mesh filter. Unfortunately this only changes 3.8L of oil with 5L of dirty oil and abrasive particles still remaining in the torque-convertor & gearbox.
To change all 8.8L of oil requires the following procedure: two large 20L buckets, one with 10L of oil, the other empty; hoses to the ATX oil cooler are removed and extended into the empty bucket; the engine is started for 1 second and the hose ejecting oil is left in the empty bucket whilst the now identified oil-intake hose is moved to the bucket containing fresh oil; the engine is restarted and run until only clean oil exits. Two people are required and Dealers do not perform such a service as routine - it must requested. Complete oil changes will greatly extend the life of the ATX.
Complete oil changes as per the procedure above are DIYable, with a cost of 30$US versus 2500$US for a gearbox repair they should be considered mandatory.
-- Inline ATX Oil Filter
The mesh filter on the 4EAT ATX oil pan filters only to 200 microns. Inline ATX-specific filters can be fitted which filter down to 50-10 microns and so remove abrasive clutch material as it occurs rather than circulating it around torque-convertor, clutches, valve-body, oil pump. Traditional "spin-on filters" & adapters are available.
