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Transmission Fluid Color and Odor Warning Signs

Vehicle repairs can be costly and lead to downtime no one wants. This is why proper maintenance and early detection are so crucial. Discovering a problem early can save you money and might save your car. One test we regularly do on all our vehicles is to check our transmission fluid level, color, and smell. This quickly can indicate if there’s a problem with your transmission or alert you to a potential problem. Let’s dive in!

What Does Bad Transmission Fluid Look Like? Good vs Bad

What Is Transmission Fluid?

Transmission fluid is a hydraulic oil that acts as a lubricant, coolant, and working fluid in vehicle transmissions. As a lubricant gears clutches and any moving parts are bathed in the fluid preventing the erosion of metal components. The transmission fluid also conditions the seals and gaskets to prevent leaks.

In automatic transmissions, the fluid also acts as a working fluid meaning that it’s actually a part of the driveline. The torque converter uses the fluid to transfer power between the engine and gears and will not function at all without it.

How Torque Converters Work! (Animation)
Transmission fluid is a working fluid in automatic transmissions

Lastly, the fluid is also used to cool the transmission. Heat builds up in the metal parts as they turn and need to be kept within operating temperatures to prevent damage. Sometimes in heavy-duty applications external cooling (radiators) are used to cool the transmission fluid and keep everything operating properly.

Transmission
Transmission fluid both lubricates and acts as a working fluid to transfer power in automatic transmissions.

How Do You Check Transmission Fluid?

Your oil isn’t the only lubricant that needs changing, but transmission fluid lasts much longer. In most vehicles, you can easily check the transmission fluid by checking the dipstick underneath the hood. Make sure to locate the transmission fluid dipstick and not the oil dipstick. The transmission dipstick is usually further back in the engine bay with a specific color or a transmission symbol.

The color and level of the transmission fluid will tell you about the health of your vehicle. With the engine warm and idling in neutral, pull out the transmission fluid dipstick and wipe it clean with a rag. Then replace it and pull it out again. The stick will indicate the level; full, low, or fill. Against a white paper towel, check the transmission fluid color.

However, some cars have a sealed transmission, which you can’t check. Your vehicle should alert you to a necessary transmission fluid change. Other cars require you to pull a plug rather than check a dipstick. Usually, these cars have a sensor that tells the computer if it’s low, and service technicians can check it with a computer.

What Color Is Transmission Fluid?

Transmission fluid is actually a clear color, but for automotive use, it is dyed bright red. Over time the color may change. It gets darker and turns into a dark brick-red color after months or years of use. This is completely normal. However, when it turns to rust-brown-red, you’ll want to schedule a service visit soon. If you notice a burnt appearance or dark brown or black transmission fluid color, don’t waste any time and get your vehicle to a service center asap.

Trans fluid should also be clear. If your fluid is milky or opaque (you can’t see through it) something is wrong. This could indicate a low fluid level churning air, water in the fluid or particulate matter building up.

Transmission fluid is basically the same as hydraulic fluid and in tractors and heavy machinery, it may be clear. This is completely normal but the color chart remains the same. Dark or milky hydraulic fluid needs to be changed or investigated.

Pro Tip: If you’ve ever wondered why a transmission is called a transmission, we uncovered How These Common Car Parts Got Their Names.

Transmission Fluid Color and Smell Check Chart
Here Is A Simple Transmission Fluid Color and Smell Check Chart

What Should Transmission Fluid Smell Like?

Transmission fluid should just smell like oil, although some people think it has a sweet aroma. The only way to know the smell of new transmission fluid is to give a sniff from a new bottle. Like the color, the smell might change over time. If you start to notice a burnt smell when you check the dipstick, this indicates a problem, and you need to schedule an appointment with a technician soon. Combined with a dark brown or black color, this could be a severe problem with your transmission.

smelling transmission fluid is part of a check.
Giving your transmission fluid a sniff is part of checking it.

Does Transmission Fluid Color Change?

Transmission fluid has red dye to help identify it from other lubricants. It remains a translucent red color as long as it’s healthy. Even if it turns a dark brick-red, it’s still normal and you do not need to be concerned. However, as the vehicle ages, the transmission fluid color could change to brown or black. This means it’s worn too far, or at the very worst, contaminated and needs a fluid flush.

Does Transmission Fluid Odor Change?

Your transmission fluid should never have an odor. Although the color darkens over time, the smell shouldn’t change much. If you ever smell burnt fluid, this indicates contamination.

What to Do If Your Transmission Fluid Is Brown

Brown transmission fluid means oxidation has begun. This means the additives that help prevent wear on your transmission are no longer as effective. You’ll need a fluid flush soon; otherwise, the fluid can deteriorate quickly. A very dark brown or black color, along with a burnt smell, means you need to get your vehicle to a shop immediately because the transmission isn’t receiving the lubrication it needs to function properly.

Pouring red transmission fluid
If your transmission fluid is no longer red, take your vehicle to a mechanic as soon as possible to get it fixed.

What to Do If Your Transmission Fluid Smells Burned?

Just like if you see a dark brown or black color when you check the transmission fluid and if the lubricant smells burned, it’s time to make an appointment to service your vehicle. Don’t waste time as the life of your transmission is in jeopardy. Burned transmission smell can be caused by bad clutches, overheated transmission or blocked fluid pathways. These items usually require a rebuild or repair of the trans.

Pro Tip: Protect your investment by uncovering Do Bigger Tires Affect Your Truck’s Transmission?

Is Leaking Red Fluid a Problem?

Leaking red fluid underneath your car is almost always transmission fluid. This is why it’s translucent red, to begin with, so you can distinguish it. Any leak should be identified, but some are so small you can ignore them. If the transmission is just slightly damp and collecting dust, you need to keep an eye on it. However, if there are drips on the ground the leak needs to be fixed.

Brown transmission fluid being removed
Changing transmission fluid is usually a big mess as there is not always a drain plug.

Other Warnings Signs That Indicate Transmission Problems

If you check the dipstick and the transmission fluid is still a red color and doesn’t need changing, you may notice other warning signs that indicate your transmission isn’t functioning properly. The lubricant is only one piece of this crucial vehicle component.

1. Your Vehicle Struggles to Switch Gears or Get Going

You’re likely facing a transmission problem if you sense your vehicle struggling to switch gears. You might also experience the gears impulsively slipping in and out of place. Not only is this scary, but it’s also dangerous. If you hear the engine revving during a gear change or delay in acceleration, there’s a transmission problem.

2. You Notice a Burning Smell

We can’t reiterate enough how crucial noticing a burning smell is when taking care of your vehicle’s transmission. Your transmission could be overheating, thus the lubricant isn’t clean and running through the system correctly. A burnt smell could also mean the fluid is old and burnt.

3. There’s Grinding Or Shaking When Gears Change

Struggling to switch gears or slipping gears can indicate a problem with your transmission, but grinding or shaking can also be a telltale sign of a bigger issue. Manual transmissions may have a slight shake, but automatic transmissions should operate smoothly. If you sense that the gears aren’t shifting the way they should visit a service shop soon.

4. There Are Noises When Vehicle Is in Neutral

Finally, you may have a transmission problem if you hear noises when your vehicle is in neutral. These noises could mean you need a fluid flush, so checking the dipstick at this point is a good idea. If you notice a darkening red color, it’s likely your transmission fluid needs a change shortly. However, if the fluid appears the normal red color, you may have a more significant transmission problem.

How to Identify Car Fluid Leaks by Smell and Color with Scotty Kilmer

Pay Attention to Your Transmission Fluid Color and Stay Safe

The color and smell of your transmission fluid are clear signs of the overall health of your transmission. Pay attention so that you can catch a problem before it becomes a larger issue. Just like changing your oil and replacing your tires are regular maintenance tasks to keep your vehicle in good working order, checking your transmission fluid is also cr.

When is the last time you pulled out the dipstick and checked your transmission fluid color and smell? Tell us in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Raymond

Sunday 16th of July 2023

The torque converter is the liquid coupling that allows the engine keep running while the vehicle is stopped and the transmission remains in gear. The torque converter can produce a tremendous amount of heat especially when the vehicle is pulling a heavy load. The torque converter literally beats the trans fluid to death. Transmission fluid constantly flows through the torque converter and the rest of the transmission while in use. If your trans pan doesn't have a drain plug, one can be added. Most auto parts stores sell a drain plug kit for about $10. FYI, you'll have to drill a 1/2" hole in the pan, clean up all burrs then tighten the drain plug in place.

Mortons on the Move

Wednesday 2nd of August 2023

thats a great idea, so few trans even have drains.