Cold temperatures thicken conventional ATFs. They circulate poorly, leaving shifting sluggish and protection minimal. Automatic transmission fluid. The lube's complex, but the decision's not. It protects clutches, planetary gears, valves, pumps and seals from damaging sludge and varnish deposits.
Transmissions usually operate under severe service conditions.
They are subject to extensive idling, frequent short trips, cold temperature driving, sustained hot weather driving or trailer towing. When conventional transmission fluids are used, they should be changed every 15,000 to 30,000 miles. Drain intervals may be extended indefinitely when fluid analysis is used.