Dear Car Talk:
I have a 1998 Toyota Tacoma pickup with 210,000 miles. I change the automatic fluid whenever the transmission "feels" like it needs it, which tends to be about the time I get to the recommended fluid-change interval. I also have a 2005 Lexus ES 330 with 188,000 miles. The owner's manual suggests continuing to change the fluid on a regular basis, regardless of the age of the car. Some mechanics, including the local dealer, suggest NOT changing it: "That could cause more problems." I assume that means scale would be loosened and could clog up the moving parts. What do you suggest -- continuing to change the oil and flush the entire system? You probably can guess that I like keeping vehicles a long time, so proper maintenance is important -- as soon as I figure out what it is!
We've heard one or two stories like that over the years. The story goes like this: A guy has an ancient car, and decides to change the transmission fluid. A few days later, the transmission buys the farm and the car is toast. That's how these "old mechanics tales" get started.
But here's what really happened: The guy with the 1966 Rambler with 180,000 miles on it noticed that his transmission was misbehaving. And that's why he decided to change the transmission fluid in the first place!
So the transmission was already on its last legs. And when, shortly after the fluid change, the transmission dies, the guy blames it on the fluid change -- instead of the 180,000 miles he had on the car, and the drag racing and donuts his 16-year-old kid does with it every Friday night.
So we think this theory is nonsense. The purpose of hydraulic transmission fluid is threefold: It transfers the power from the engine to the wheels; it lubricates all the parts of the transmission; and it keeps those parts cool. And for every one of those tasks, new, clean fluid is better than old, crusty fluid with old pieces of broken-off transmission in it.
So not changing the fluid after a certain mileage is like telling your 96-year-old grandfather, "We're not going to feed you anymore, Pappy, because it might cause more problems."
Good maintenance includes changing the fluids at the mileage intervals that the manufacturer recommends -- no matter how old the car is. And you're more likely to drive it into old age if you drive it gently and follow the maintenance schedule.