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What Color Is Transmission Fluid? Does the Fluid Color Matter?

filling up car engine with new transmission fluid

Just like the engine, the transmission needs fluid to operate. Without it, you’ll have extensive friction, overheating, and premature failure on your hands. But what does this fluid look like, or, rather, what color is it? If it came from a brand-new canister, the oil would be bright red. However, it changes the color over time and turns brown or even black.

Ideally, the fluid should be translucent. That means it’s pure and not contaminated by any burns or metal shavings. Today, we’ll talk about the very definition of transmission fluid, how to check its color and how to use that information to determine whether it’s time for a replacement. We’ll also go over the process of flushing and changing it. So, stay tuned!

car and road dividerTransmission Fluid/Oil: Why Is It Important?

Like the fluid that we add to the engine, brakes, or radiator reservoir, transmission oil has one important job: minimizing metal-to-metal friction. By lubricating the various mechanical parts, the fluid prevents premature wear and tear, increasing the transmission’s lifespan. Along with that, it eliminates the chance of overheating.

Oxidation and rust can also ruin a perfectly fine transmission. But the fluid protects the gearbox from that as well. All you need to do is make sure the levels aren’t very low and that the fluid is not contaminated by sludge, deposit, or metal powder/shavings from wear.

mechanic draining the old automatic transmission fluid
Image Credit: PongMoji, Shutterstock

So, What Color Is It?

Healthy transmission fluid is always clear-colored, bright red. Manufacturers add a dye into the mix to make it easier to distinguish transmission oil from other fluids. We’re talking about engine oil (amber or yellow), the coolant/antifreeze (mostly green, but can also be blue or pink/red), brake fluid (clear, translucent, yellow), or steering fluid (light red).

So, even if you’re just a regular driver that doesn’t work with cars all day, it won’t be hard to figure out that you are, indeed, dealing with transmission fluid. Also, it is slicker and thinner than engine oil. As for the smell, it’s mostly odorless but slightly sweet and very similar to that of petroleum.

Does the Fluid Color Matter?

Yes, it most certainly does. Here’s a quick breakdown:
  • As mentioned, transmission fluid that comes from a fresh canister will have a translucent, bright red color. After 6–12 months, it will get a bit darker, but not too much. At this stage, you have nothing to worry about, as it is still efficient and won’t let the transmission fail.
  • What if it’s brown? In that case, you’re dealing with contaminated, oxidized fluid. Don’t raise the alarm just yet, as this is 100% natural, and not only with transmission fluid but with car fluids in general. Now, it might also be burnt, which is a cause for concern.
  • In the worst-case scenario, it will be black. That, in turn, is a clear indication that the fluid is way beyond topping it off. Black oil won’t be able to adequately lubricate the transmission. You won’t get proper cooling or anti-rust protection, either. In fact, it will do more harm than good. So, flushing is the only option here.
  • The sludge and deposits that sit at the bottom will clog the transmission, leading to problems with gear shifts, weak performance, strange noises, smells, and more.
  • When left untreated, the fluid may even start to leak. You should see it dripping from the front of the vehicle. Use this opportunity to check its color. Chances are, it’s still bright red. If so, all you’ll have to do is secure the pan. Most likely, the bolts are loose, and that’s why the fluid is leaking.
  • In some rare cases, you’ll see the red turn pink. That means you’re dealing with water/coolant contamination. Hopefully, repairing the transmission will fix this. If not, you’ll have to buy a brand-new unit.

Checking the Transmission Oil Color

If you don’t want to crawl underneath the car, remove the pan and the filter and run the risk of getting your clothes dirty, there is a hassle-free way to check the fluid:

  • Park the car, but don’t turn the engine off. Instead, keep it running and warmed up. With some vehicles, the motor needs to be off during this procedure, though.
  • Check with the owner’s/service manual to get this right. Otherwise, you might end up damaging the transmission.
  • Can’t seem to find the manual anywhere? Reach out to a local dealership—they should be able to help, especially if you’re driving a relatively newer car.
  • Make sure the car is sitting on a level surface. Pop the hood and find the dipstick. All you have to do next is pull it out and give it a nice cleaning. Put it back in, secure it (the dipstick should go all the way), and pull it out one more time. Now you can get a proper reading on the fluid.

This will not only allow you to see what color the fluid is but also check on its level. If it sits below the “Hot” mark (or it could just be a dot or a line), you’re running low on fluid. A quick note: in some cars (especially with manual transmissions), there are no dipsticks at all. Mechanics will still be able to get a read, however.

How Long Does Transmission Fluid Last?

This greatly depends on the transmission type. If it’s a manual one, expect it to work for 30–60K miles, which equals 2–4 years straight. And if it’s an automatic transmission, the life cycle will be significantly longer: 60–100K miles (or 6–7 years). The exact lifespan will be determined by your driving style, the area that you live in (hot and humid or cold and dusty), and other factors.

For example, if you constantly push the car to the limit, a fluid change might be necessary at the 15–20K mark. We’re talking about towing, hauling, and aggressive driving. This is important: while fluid changes have to be more frequent with manual transmissions, these units actually last longer. Plus, they’re a bit more fuel-efficient.

Of course, nothing bad will happen if you change the fluid every 10–15K miles. It will cost you extra but won’t damage the system in any way. Some manufacturers claim their fluids are good for 100K+ miles, but they usually don’t last that long.

Can You Change Transmission Oil Manually?

Yes, this is a relatively simple procedure. We already talked about how to measure the liquid level. To add new fluid, set the transmission to “park”, engage the parking brake, and keep the engine running. Next, pop the hood, grab a funnel, and put it into the dipstick hole. Now just slowly pour the new fluid into the funnel.

Use the dipstick to see how much fluid you’ve added. Disengage the parking brake and switch through every gear to let the fluid “spread out”. Go back and take another look at the fluid levels—you might have to add a bit more. Drive around the block once or twice to test the transmission out, and that’s it!

Should You Top It Off, or Not?

This is a rather common practice. However, keep in mind that the new, clean fluid will be mixed with the dirty oil already there. So, only do this if you’re absolutely sure that the factory fluid isn’t contaminated by sludge, metal shavings, or anything else. This will only take 5–10 minutes. You’ll probably end up messing up the viscosity, though.

automatic transmission
Image Credit: Gorlov-KV, Shutterstock

Flushing Old Transmission Fluid

Be warned: this is a messy job. So, put on old clothes and protective gloves. To capture all the old fluid, you’ll need a drain pan. Or you can just use a bucket. Crawl under the vehicle and remove the bolts that are holding the transmission pan. We recommend only removing a couple of bolts on the right side to avoid the oil spilling out all at once.

Give it some time to drip out, remove the pan and clean it. The filter shouldn’t be hard to remove—just snap it out. It would be wise to replace it along with the fluid. Once the new filter is in place, secure the pan using the same bolts and add the new fluid through the dipstick hole as we did earlier.

car and road dividerConclusion

Many drivers don’t give much thought to the color of the transmission fluid. However, if you know what it looks like, it will be much easier to buy the right fluid and not mistake it for anything else (like coolant). More importantly, this will help determine if a flush/change is in order, or not. New transmission oil is bright red; when it’s taken over by slush, you’ll see a darker tone.

As a rule of thumb, the fresher it is, the better the gearbox will perform. Besides, you won’t have any issues like poor fuel efficiency, slow acceleration, or difficulty to start the car. So, follow our recommendations on changing the fluid, be a conscious driver, and we’ll see you next time!


Featured Image Credit: Oteera, Shutterstock

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