A clean, shining automatic transmission sits on a shop table.

Transmission Fluid Change Tips: When Is It Time for a Refill?

Questions about when it’s time for a transmission fluid change are common at any mechanic’s garage. Although this particular fluid isn’t something that requires constant attention, ignoring the proper service interval can lead to internal damage as well as reduced performance and comfort out on the road. Compounding the issue is the fact that manual and automatic transmissions have dramatically different maintenance needs.

Let’s take a look at some basic tips to help guide your transmission maintenance decisions.

What the Fluid Does

In a manual transmission, the fluid is more properly referred to as oil, because its job is to lubricate the gears while they’re in use as well as protect them from heat damage.

In an automatic, on the other hand, the fluid is more akin to a hydraulic fluid. It’s vital to the operation of switching gears in addition to regulating heat.

How to Inspect Transmission Fluid

Before a manual-transmission fluid change, you should verify whether it’s really necessary. Symptoms that indicate the time has come for an oil swap include stiff shifting and noise from the gearbox. You can also check the actual level of the oil. Most manual transmissions have a fill hole located toward the top of the unit, which is accessible by unscrewing the bolt that covers it. If you insert the end of a screwdriver into the hole and it doesn’t come back wet, then your fluid level is low. If the fluid smells burnt, is excessively dark or contains metal shavings (from the friction that occurs between gears), those are also signs that it’s time for a refill.

Automatic transmission dipstick

Automatic transmissions typically come with a dipstick located in the engine bay. Removing this dipstick will show you not just the level of fluid you have in the transmission, but also whether it’s burnt or worn out as with the manual oil. You’ll need to check the level with the car in park and the engine on, after it has reached standard operating temperature. Other signs of an automatic fluid issue include slipping gears, high rpms during highway cruising, and rough, abrupt shifting.

What About Mileage?

There’s no general consensus on how many miles you can travel before it’s time for a transmission fluid change. There are a wide range of intervals listed by a variety of automakers for manual gearbox oil, with 30,000 miles at the low end for vehicles that see heavy-duty use and 80,000 miles at the high end for a typical commuter car.

Intervals for an automatic transmission fluid change are similarly spread out. Some newer vehicles advertise “lifetime” fluids, fluids that can last 150,000 miles or fluids that can go 100,000 miles without a change.

Depending on how you drive your car and in what environment, the best way to decide when it’s time for a fluid swap is to consult your owner’s manual, talk to your local NAPA AutoCare and do regular inspections of your transmission fluid. By keeping an eye on its condition before the tail end of the recommended service interval, you can spot potential problems well before they become major issues.

Check out all the chemical products available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on a transmission fluid change, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

about author

Benjamin Hunting

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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