How to Maintain Your Car's Transmission and Avoid Costly Repairs

The simple answer is yes, but service intervals for new vehicles can exceed 100,000 miles before this is needed.

That makes this seemingly clear-cut advice something of a conundrum for car owners. Those who don’t hold on to a new vehicle for very long may never have to have the transmission fluid changed. On the other hand, any owner who plans to keep a vehicle for an extended period of time or who bought a used car with high mileage should plan to have their car’s transmission serviced.

The best advice is to know the manufacturer’s recommended service intervals for your car and how you drive it. Some cars have an alternate “severe” maintenance schedule, but most of us who aren’t using our car for towing, operating it in extreme temperatures or dusty weather, or only making short trips where the engine doesn’t get warm will not need to use it.

It’s worth noting that intervals for changing transmission fluid vary widely. For some cars and trucks, it can range from as little as 30,000 miles to more than 100,000 miles. Some new vehicles, especially those fitted with automatic gearboxes, have transmissions that are almost sealed shut, with fluid that’s meant to last the lifetime of the car.

Most CVTs (continuously variable transmissions) need inspections and/or fluid changes. We advise owners to refer to the owner’s manual for specific guidance and to keep records of related services. This will help when selling the vehicle and will also prove that regularly scheduled maintenance was performed when making a warranty claim.

Remember that, unlike engine oil, transmission fluid should never burn off. A telltale sign of a transmission leak is a puddle of red liquid on the ground, usually under the middle or front of the car. 

It’s helpful to understand the role transmission fluid plays in a car’s operation. Transmission fluid helps keep mechanical components cool and lubricated, regardless of whether the gearbox is automatic or manual. Over time, the transmission’s interior components wear down, and tiny particles contaminate the fluid. This could potentially lead to damage.

Getting rid of this dirty fluid makes sense, right? If it’s called for in the automaker’s service manual, go ahead and let your mechanic perform the work.

"This shouldn’t be a frequent occurrence, since a gearbox in good working order would not have metal shavings polluting the fluid over a short period of time," says Consumer Reports’ chief mechanic John Ibbotson. "If that’s the case, it’s likely a sign of a bigger and more complicated problem."

"There is also a distinction between simply draining and refilling a transmission vs. power-flushing the system," he says. "In a high-mileage car, power-flushing the transmission fluid can dislodge sludge and other particles, leading to clogs even after the clean fluid has been added."

Again, the best advice is to research your vehicle and know exactly when a transmission drain (or flush) is recommended. Doing either option too often is a waste of time and money. Be wary if a dealership service advisor or your independent mechanic pushes this service with every visit. Ask them to show you where the automaker recommends the process be performed and at what mileage. As always, stick to the automaker’s recommended service schedule.

Yes, even a manual needs transmission fluid. The type of fluid can vary from car to car, however. Some manuals require conventional engine oil, and others function best with automatic transmission fluid. So, make sure you’re putting in the fluid that’s specified for your car. Failing to do so can rapidly affect its performance and the gearbox’s longevity.

Car owners with a CVT should also pay attention to their vehicle’s needs. Unlike a traditional automatic with a set number of gears, a CVT often relies on a belt or pulley system to provide an infinite number of gear ratios. Make sure you use a CVT-specific fluid, or you’ll risk big headaches (and repair bills) down the road.

Checking transmission fluid isn’t always easy. In many cases, it’s necessary to have a mechanic put your car on a lift for an inspection. Some cars have a transmission dipstick or reservoir in the engine bay, so check under the hood first.

Even though fluid levels might look fine, it may be difficult to determine whether the fluid contains pollutants or small metal particles. "If your car is in for routine maintenance, ask your mechanic to check the transmission fluid," Ibbotson says.

Separating transmission maintenance from breakdowns is trickier. In a malfunctioning automatic transmission, gearshifts might become more abrupt and occur at awkward intervals. For a car with a manual gearbox, the feel and action of the gear lever could become stiffer and more balky in regular daily operation. These types of problems probably indicate an issue with the gearbox itself. If you experience any of them, let your mechanic know right away. 

Servicing your transmission can be a complicated and messy task for the average car owner. "Accessing the transmission requires ramps, jack stands, or a lift," Ibbotson says. "Even then, getting to the fill plug can require a higher degree of patience and dexterity than what’s required for a typical change of engine oil."

Many modern cars have transmissions that are basically sealed tight or require a dealer’s service computer to read temperature and other parameters, making them all but impossible for the average do-it-yourselfer to work on.

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