How To Check Transmission Fluid
Start by consulting your owner's manual.
Time Needed: 10-30 minutes, Difficulty: Easy, Cost: $0-20
As far as bad automotive sensations go, a slipping automatic gearbox is up there with the sound of rod knock and the smell of burnt wiring. It could be caused by a leak, a blocked transmission cooler, or fluid that’s past its change interval. The good news is that an ounce of active maintenance will prevent you from reaching that point, and checking the level and condition of your car’s transmission fluid is usually pretty easy.
Transmission fluid is often neglected, particularly as certain automakers have experimented with the concept of “lifetime” fluid over the past quarter century or so. In reality, lifetime fill just means that when the fluid breaks down and takes out the transmission, that’s the end of your car’s lifetime. However, the aftermarket giveth what the OEMs taketh away, so owners of certain dipstickless cars aren’t completely out of luck.
Additionally, a good portion of average North American driving is considered severe duty. Extreme heat, extreme cold, stop-and-go traffic, and driving over loose terrain can shorten the lifespan of your transmission fluid, so periodic inspection is paramount to keeping your car’s performance up to spec.
Now that you’re up to speed, let’s talk about how to do it.
The Safety Brief
As with any engine bay work, you’ll want to wear safety glasses and gloves when checking transmission fluid. Doubly so if your car’s manual recommends checking transmission fluid at operating temperature, where scalding hot drips of fluid can do nasty things to human skin. In addition, be sure to wipe up any drops of transmission fluid that may come off the dipstick. Transmission fluid is quite flammable, so reducing the risk of a car-be-cue is generally a good idea. It’s also crucial to use jack stands if you plan to raise your vehicle with a jack.
The Tools & Parts You Need
The most important tool in this job will be your owner’s manual or service manual that will tell you what type of transmission you have and how it can be checked. If your automatic transmission comes equipped with a dipstick, the only tool you’ll really need is a rag or paper towel to wipe down the dipstick.
Transmissions with a sealed-for-life design require a little more expenditure and creativity. For instance, the Mercedes-Benz 722.6 automatic transmission never shipped with a proper dipstick, but aftermarket solutions exist to permit checking fluid level and condition. You’ll also need a small pick to unclip the pin that holds the inspection tube cap on.
Some gearboxes, like the ZF 6HP, have variants with tiny dipsticks only accessible from underneath the vehicle. You’ll need a jack, jack stands, the correct socket for the dipstick and a trim tool set to remove any applicable underbody paneling.
The Task: How To Check Transmission Fluid With a Dipstick
Let’s get after it.
1. Look up the fluid check procedure for your particular transmission.
Most manufacturers require the transmission fluid to be up at operating temperature for a correct reading. Make sure your vehicle is parked on a level surface, as an incline can drastically affect fluid level readings, too. It’s also a good idea to put the parking brake on. Read the details in your owner’s manual or service manual, and proceed as instructed.
2. Locate your car’s transmission dipstick.
It will most likely be located under your car’s hood and should be distinguishable from the oil dipstick thanks to its red coloring. I might also be located underneath the vehicle.
3. Pull the dipstick from its tube, wipe it off with a paper towel, and re-insert it.
This will clean any splatter to ensure an accurate reading.
4. Draw the dipstick once again and take a good look at the fluid reading.
Transmission fluid should be pink, so if it looks as dark as the night sky, change it as soon as possible. If it smells burnt, that’s a really bad sign of clutch material now suspended in the fluid.
5. Wipe the dipstick off one more time and push it back into its tube.
Ensure it’s fully inserted to avoid any unexpected evacuation of fluid. Transmission fluid burns really easily and getting any of it on a hot exhaust manifold usually spells disaster.
6. Add new/more transmission fluid if needed.
If your transmission is leaking, and your fluid level is low, you will need to immediately address the situation. If it’s a small difference, you can add the appropriate amount, but if it’s a lot, you likely have a big problem that should be resolved before continuing to use the vehicle.
Here’s an Example of a Manufacturer-Specific Process for a 2018 Chevrolet Tahoe:
How To Check Transmission Fluid Without a Dipstick
If your vehicle does not have a dipstick, consult your service manual to determine if it’s possible to check it. The transmission might have small windows or readouts that allow you to check it without opening it up. Otherwise, you can check a sealed transmission by opening it up, but that’s a job best left only for extreme situations when you know something is wrong. If that makes you uncomfortable, consult a professional.
FAQs About Checking Transmission Fluid
Car Bibles answers all your burning questions.
Q: What are the signs of low transmission fluid?
A: While low transmission fluid used to mean a puddle would form under your car, modern underbody aero paneling often prevents leaks from making it to the ground. While monitoring fluid condition by routinely checking the dipstick is the best method of problem prevention, there are other tell-tales of low transmission fluid. Look for clumsy shifts that can vary from harsh to slurred, as well as delayed engagement when shifting into drive or reverse. When dealing with a continuously variable transmission, make note of any undue belt slip that may feel similar to a slipping clutch.
Q: What happens if you drive with low transmission fluid?
A: Very bad things. In an automatic transmission, the fluid both lubricates and cools paper-thin transmission clutches. Run low on fluid and the clutches could sustain damage, ultimately culminating with gears disappearing. Likewise, continuously variable transmissions use special fluid with a friction modifier so the belts can grip the pulleys. Running low on CVT fluid could cause catastrophic belt slip and ruin the transmission. Either way, running on low transmission fluid could lead to a very expensive transmission rebuild or replacement, often costing thousands of dollars.
Q: When should you check your transmission fluid?
A: While modern cars don’t require nearly the same intensity of maintenance as older vehicles, it’s still a good idea to check your transmission fluid once a month. While you’re under the hood, also keep an eye on brake fluid, power steering fluid, coolant, and oil levels.
Watch This Helpful Video To Learn More About Transmissions
We at Car Bibles recognize that text-based learning isn’t for everyone. Parsing technical instructions can be arduous and video is an awesome resource as it gives frame-by-frame visual references. For all the visual learners out there, we’ve got you covered with EricTheCarGuy’s video showing you how to check transmission fluid. Eric’s a veteran automotive technician with 1.65 million YouTube subscribers at the time of writing, so it’s safe to say we trust his tutorials on vehicle maintenance.
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