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How to Check Your Transmission Fluid

You check your engine oil between services – or at least, you should. You’re looking for the proper level and condition, and if there are any signs of a problem, you change the oil. Where engine oil is the substance that keeps your motor in good shape, an automatic transmission relies on its own fluid to maintain its operation. But do you know how to check transmission fluid in your car

Just like engines have a dipstick, transmission assemblies do in most cases too. Keeping an eye on this long-lasting but extremely important fluid should be as routine as checking the engine oil. What does bad transmission fluid look like, and how do you check the fluid level? Here’s what you need to know about checking transmission fluid.

What functions does transmission fluid play?

To understand why transmission fluid needs to be checked as part of a regular maintenance routine, it helps to know what it does. Many car owners believe that the fluid’s only purpose is to lubricate the moving parts inside the transmission. While that’s true, there are additional functions it performs.  

Transmission fluid:  

  • Lubricates moving parts to prevent wear, as mentioned. 
  • Reduces friction between components to improve efficiency. 
  • Cools parts to prevent overheating and damage. 
  • Acts as hydraulic fluid for the valve body to change gears. 
  • Coats metal parts to prevent oxidation and corrosion. 
  • Conditions seals and gaskets to prevent leaks. 

It really is crucial to keep transmission fluid clean and full, or any of these functions could be compromised. 

Why is it important to check your transmission fluid? 

Like any system in your vehicle that uses a fluid – engine, cooling system, brakes, differentials, and power steering included – it only works as designed when the correct fluid is contained within the system at the proper level, and in good condition.  

If the transmission fluid isn’t at the proper level or in good shape, it doesn’t just stop driving or changing gears. An automatic transmission fluid problem often causes serious concerns like burnt clutches, blown seals, or broken gears. Neglecting the simple service item could result in a repair or replacement costing thousands of dollars. 

Symptoms of Low Transmission Fluid 

What are the signs of low transmission fluid? If the transmission fluid is lower than it should be, symptoms often show up. You might notice that it feels like it drops out of gear while you drive, resulting in the RPMs flaring. When you’re accelerating at a stop, you might need to rev the engine up a bit before it engages and starts to move your car. Eventually, you could smell a pungent burning smell from overheating in the transmission.

Of course, there’s a reason the fluid is low too. There’s a good chance you’ll see drips on the ground, potentially from a leaking seal or transmission cooler hose, or it could be from damage to the case itself.  

In most newer vehicles with an OBDII diagnostic system, the Check Engine Light will come on when the fluid is sufficiently low. Codes related to loss of prime often indicate the fluid is too low.  

Steps for Checking Transmission Fluid Level 

Your car’s owner’s manual is the authoritative source for how to check the transmission fluid level since not all cars are the same. Here are some general tips for checking the fluid. 

1. Locate the dipstick

Under your vehicle’s hood, check for a dipstick that extends down toward the transmission. This is where to put fluid if it’s low too. On a 4WD or RWD vehicle, it tends to twist toward the firewall while on FWD and AWD vehicles, it’s typically beside the engine. The top of the dipstick usually has a gear-shaped symbol stamped on it.

Not all cars have a dipstick, though. Some foreign brands like BMW don’t include one with the vehicle from factory, so relying on dealer services is how to check transmission fluid. Other models equipped with a CVT transmission may not have a dipstick either, and a service facility needs to check the fluid for you.

2. Check it warm and in park

The transmission fluid should be checked when the vehicle is warm and the transmission is in park on a flat, level surface. Since you want the fluid level checked after it has circulated and filled the lines and areas inside the transmission, you shouldn’t check it when the car is stone-cold.

3. Identify the level

On the dipstick, locate the low and full levels. There might be a hash-marked section indicating a normal range or there could be words like “MIN” and “MAX” or “FULL” and “ADD”. It should be within the minimum and maximum levels for normal operation.

What to Look out for While Checking Your Transmission Fluid 

Of course, low fluid requires that it’s topped up. If the fluid is lower than the minimum mark, add fluid of the exact type your owner’s manual specifies. If in doubt, ask an AutoZone associate for assistance determining the right fluid, and they can also advise you on how to add transmission fluid. 

Make sure you also check the fluid condition. For most cars, the fluid begins its life a reddish-pink color and changes to brown as it ages. If it’s dark, feels gritty when rubbed between your fingers, or smells burnt, it’s time to change the fluid. 

How Often Should Transmission Fluid Get Changed? 

How to Change Your Transmission Fluid – AutoZone How to Videos

Like engine oil, transmission fluid needs to be changed to prevent mechanical problems and to maintain its benefits mentioned earlier. For some cars, the interval to change the transmission fluid can be 100,000 miles or five years. For vehicles that experience severe service like trucks that tow, the interval could be just 20,000 miles.  

Transmission fluid changes are more expensive and can cost a couple hundred dollars or more, but since they’re required much less frequently than an oil change, the service averages out to even less per mile.  

Your best bet to determine when the transmission fluid needs to be replaced is by following the maintenance schedule and keeping an eye on the fluid condition and level. If the fluid is dirty before the interval arrives, play it safe and change it. 

If you’re transmission fluid is low or have you have a leak, contact a service professional to have it checked and addressed. You can get transmission fluid at AutoZone, no matter what make or model you drive. If you need help choosing the right fluid or assistance on how to fill transmission fluid, an associate would be happy to provide Trustworthy Advice. 

If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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