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Taking care of your car or truck’s transmission is important for its long-term health. But all too often, car owners misunderstand the basic maintenance that’s needed to keep a gearbox running smoothly. Consumer Reports’ chief mechanic, John Ibbotson, explains what you need to know.

Do You Need to Have the Transmission Fluid Changed?

The simple answer is “yes.” But service intervals for new vehicles can exceed 100,000 miles before this needs to be done.

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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, factoring in that service is good advice for any owner who plans to keep a vehicle for an extended period of time—or for someone who has bought a used car with high mileage.

The time and cost involved vary from car to car. According to RepairPal, a CR partner, getting this work done on a 2010 Camry in Rochester, N.Y., should cost $163 to $242.

Whatever the price might be, it’s necessary work. Getting the fluid replaced is certainly going to cost you less than replacing a transmission that’s been left in the lurch by skimping on service requirements. Failing to properly maintain your car’s transmission could leave you stranded and with a big repair bill.

Simple online tools can be invaluable when it comes to knowing whether your car or truck has been subject to any recalls. Other than regular service, your transmission might be due for some important repairs—or have an extended warranty—because of a past recall. (Go to the CR Car Recall Tracker.)

How Often Do You Need to Have the Transmission Fluid Changed?

The best advice is to know your car and the manufacturer’s recommended service intervals.

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 transmission) 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.

Remember that unlike engine oil, transmission fluid should never burn off. And a tell-tale sign of a transmission leak will be a puddle of red liquid on the ground, usually underneath the middle or front of the car.

Should Your Mechanic Flush the Transmission Fluid?

First, it’s helpful to understand the role transmission fluid plays in a car’s operation. Transmission fluid helps keep mechanical components cool and lubricated, whether it’s an automatic or manual gearbox. 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 service manual, go ahead and let your mechanic do the job.

“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," Ibbotson says. "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 versus power-flushing the system,” he adds. “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.

Does a Manual Transmission Need Fluid, Too?

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 continuously variable transmission (CVTs) will also want to pay special attention to the needs of their vehicle. Unlike a traditional automatic that has a set number of gears, a CVT often relies on a belt or pulley system to operate 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.

How Do You Know Whether the Transmission Fluid Needs to Be Changed?

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

Even though fluid levels might look fine, it could be harder to discern whether there are pollutants or small metal particles in the fluid. “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, 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.

Is Changing the Transmission Fluid an Easy DIY Job?

It can be a complicated and messy task for the average car owner. “Accessing the transmission requires ramps, jackstands, 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 dealer’s service computer to read temperature or other parameters, making them all but impossible to work on for the average DIY’er.

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