Despite the significant advancements in modern transmissions and the “fill-for-life” fluids used by some manufacturers, automatic transmission experts say fluid should be periodically changed to ensure maximum transmission life.

The transmission is an integral part of your vehicle. It’s one of the key components in delivering power to the wheels and allowing movement forward and backward. Keeping the transmission in good condition is also in the best interest of your pocketbook. Depending on labour rates and the extent of a failure, rebuilding a tranny can typically cost between $3,000 and $5,000.

How often fluid should be replaced depends on the type of driving you do. Your vehicle’s service manual contains recommended maintenance intervals. Look online if you can’t locate the hard copy, or call the dealer or manufacturer.

“Manufacturers started going to what they called ‘fill-for-life.’ To the consumer that meant you didn’t have to take your transmission in every 30,000 miles [48,280 kilometres] like you did back in the ’90s.” says Lance Wiggins, technical director at the California headquarters of the Automatic Transmission Rebuilders Association (ATRA). ATRA has accredited members in transmission repair shops across Canada.

“This transmission fluid will be good until the transmission decides it’s going to fail, which isn’t until 140,000 to 160,000 miles, so the consumer felt comfortable with that statement. The reality is, though, all transmission fluid should be changed. It will allow your vehicle to last longer, especially if you’re driving in the city in comparison to driving highway mileage.”

Transmissions are designed to operate at high temperatures, but consistent overheating can break down the fluid.

“City mileage tends to warm the transmission up much more frequently over the long haul than it does on the freeway,” Wiggins says. “So, somebody that has 30,000 miles on a vehicle in a couple of years due to highway mileage in comparison to someone that has 30,000 city miles in three or four years; the city-mileage transmission fluid will actually be more deteriorated than the highway-mileage fluid. And that’s due to heat, and that’s what basically breaks down transmission fluid and causes transmissions to fail.”

Let’s look at a possible scenario where the transmission fluid has never been changed. Wiggins uses the analogy of burning grease on a frying pan.

“That’s basically what happens to your transmission fluid. Eventually that fluid will become tarnished. It will become black or dark, dark, cherry red, and that’s when the fluid viscosity starts breaking down. Once that happens, the friction clutch plates inside the transmission fail to hold their friction, and they start slipping. When that slipping happens, that’s when the transmission fluid really starts to get hot. And at that time there isn’t anything the radiator or cooler can do for it. It’s already too late.

“So you’ve reached a critical point in the transmission where all of a sudden you start feeling maybe it doesn’t shift like it used to,” says Wiggins. “It’s kind of weird, it feels like it’s slipping, you’re not really sure what’s going on with it. You don’t have any codes, there’s nothing tripping the customer to check it out, there’s no big red light that says something is wrong. Then all of a sudden after driving like that for a couple weeks it trips the code. You take it to the dealership or transmission shop and at that point you get the unfortunate news that your transmission needs to be repaired. Normally, it’s out of warranty by that time.”

To help extend the life of your transmission, ATRA recommends changing fluid every 50,000 km, or two years.


Article originally published by Joanne Will in the Globe & Mail – 30.10.13