The controversial question of when to change the fluid in the 5R55E automatic transmission – have done much research & thought I would share what I found – not an endorsement of what maintenance plan to follow Changing the fluid in the 5R55E (5 speed automatic) transmission used in the 2000 Explorer and some earlier and later years. The maintenance manual that comes with the Explorer says change transmission fluid at 30K intervals for 5 models of transmissions (AX4S, AX4N, 4R70W, 4R100, 4F27E). The 5R55E transmission is not referenced. The manual repeats this maintenance schedule at 30K intervals until 150K, at which point it just says change the fluid and filter with no transmission model reference. The manual is not at all helpful trying to figure out what the recommended fluid change interval is. So I called Ford. Ford customer service does not know what the “factory” recommended interval is!!! I asked for the phone number of someone who could help, they said there was nobody at Ford that could help. Their response was they did not have that information, and told me to call a dealer (that the dealer had access to information that the Ford company customer service representatives did not have access to). So I called 5 dealers, locally to get the answer, with not a lot of luck. Finally, on the 5th try I got referred to a service manager who took the time to check his online access to Ford information. Meantime I found the service information in the factory service manual. His answer from his Ford reference, which also matches what the Ford service manual says, says that no fluid change is recommended or required when operating under non “special operating conditions” as defined by Ford in the operators manual. So Ford says fluid is there for the life of the transmission. The knowledgeable dealer said that met the Ford warranty requirements, including extended warranties. So to change it at 30K or some other interval or wait until the transmission dies!!! And to complicate things, in my research for the answer on the internet, I heard people talking about changing their fluid at 30K or less intervals and still having the transmission fail with low mileage, while a few others talked about never changing their fluid and getting high mileage out of their transmission without a problem. All of the dealers I spoke to that recommended changing the fluid at 30K, only recommended a flush (they did not recommend or include the pan drop and filter replace). They all said the flush process they used flushed the fluid in reverse, thus cleaned the filter. At least one of them said that even though the filter is enclosed in plastic, it was not a paper filter, e.g. it was a screen that could be cleaned by the back flow flush [anybody ever take one apart, e.g. is the factory filter a screen or paper filter?].