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Low Transmission Fluid Symptoms and How to Check the Fluid Level

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 is Transmission Fluid?

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. 

Differences between Manual and Automatic Transmission Fluid

Between automatic and manual transmission-equipped vehicles, the fluids differ. While both have a base oil and additives, they’re uniquely blended to perform somewhat different tasks. 

Manual transmission fluid

  • Is usually clear, tinged slightly blue, or a very light brown color.
  • Contains fewer additives and modifiers. 
  • Is a heavier weight fluid and sometimes is the same as gear oil. 
  • Has been optimized for anti-wear, anti-foaming and load carrying.

Automatic transmission fluid:

  • Has improved viscosity over a wider range of temperatures. 
  • Has modifiers to help with smooth gear changes. 
  • Is heat-resistant and thermally stable to prevent sludge and deposits from forming.
  • Stays fluid enough for effective hydraulic function in electronics, even at low temperatures.
  • Is usually red or green in color. 

While there are some examples of manual transmissions that use automatic transmission fluid as lubricant, manual transmission fluid and automatic transmission fluid (ATF) are normally NOT interchangeable. In fact, most automatic transmission fluids aren’t interchangeable between makes and models. Performance can be affected and premature failure can result from using the wrong fluid.

What is CVT Fluid All About?

An increasingly common type of transmission in cars today, the continuously variable transmission (CVT) has fluid with unique characteristics. Most times, it’s a full-synthetic fluid with premium base oils and additives specifically designed to reduce wear and improve shear stability.

It is not the same as ATF and most carmakers have their own specs to adhere to. 

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. 

Signs 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.  

Fluid spots on the ground

Do you see spots on the driveway that are either new or growing? It could be transmission fluid. Dab the fluid with a finger or cloth to check the color. For cars with an automatic transmission, red or green-tinged fluid can indicate an active transmission fluid leak whereas clear or viscous brown fluid could be a sign of a manual transmission leaking.

Difficulty engaging into gear (manual)

When fluid is low in a manual gearbox, getting the shifter into gear becomes increasingly difficult. You might feel like it’s almost impossible to jam the gearshift into gear, especially from a stop. 

Trouble getting into gear (automatic)

Putting the shifter into drive won’t be the issue, but your automatic transmission may not engage right away. Rather than starting to roll slowly when your foot is taken off the brake, you may need to rev the engine up a little before it “catches” and you start moving. It can also drop out of gear while you drive. This ultimately can cause other issues in the transmission, like damaging the planetary output gears in the transmission. 

RPMs flare while driving

As you drive a constant speed or accelerate, your RPMs could unexpectedly flare. People commonly refer to this as the “transmission slipping”. It’s usually the result of clutches slipping inside the automatic transmission, and it could be a sign there’s already damage done. Shifts may also be harsh and the transmission clunks into gear.

Burning smell from under the hood

A pungent smell from under the hood can indicate excessive friction in an automatic transmission. It gets worse the longer you drive. The fluid itself has an extremely strong odor and has usually become quite dark compared to the original color. It’s what you’d consider burnt transmission fluid.

Check Engine Light is on

On some vehicles, the powertrain control module (PCM) may detect that the fluid pressure has dropped, and the DTC may trigger the Check Engine Light. The generic OBD-II code you’ll discover is P0868 – transmission fluid pressure low.

Noises as you drive

Low fluid can contribute to unusual noises too. It could be clunking, whining, or grinding sounds, especially when in gear and trying to accelerate.

Visual inspection

And the most accurate way to determine that the transmission fluid is low is simply to check the fluid level. 

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? 

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. 

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