Buying guide for best automatic transmission fluid
Automatic transmission fluid (ATF) is one of the most important liquids in your vehicle. Without it, things come to a grinding halt — literally. You can prevent expensive transmission problems by changing your fluid regularly according to your vehicle maker’s instructions.
The challenge comes in knowing which of the dozens of products available is the right one for the job. How do you find the best automatic transmission fluid for your vehicle? There are several things to consider, such as your vehicle’s age and manufacturer and the usual temperatures it operates in.
The BestReviews Testing Lab researched the top automatic transmission fluids on the market to provide you with everything you need to know before your next change is due. Our top pick is the Royal Purple Max ATF, which provides excellent protection for high-performance vehicles.
Which automatic transmission fluid is best?
Best ATF for high-performance vehicles
Product specifications
Container Size: 1 qt. | Synthetic: Yes | Flash Point: 395 degrees | Pour Point: -86 degrees
Our top pick, this synthetic, high-performance ATF has a low coefficient of friction, and combined with the high film strength, goes to work in the transmission immediately. Coating all the necessary metal bits and pieces, it ensures an even lubrication to reduce wear and internal temperatures.
Royal Purple claims that this ATF is more oxidation-stable than other lubricants, which gives the fluid a longer life. In theory, that means you won’t have to change the transmission fluid as often. We like that this ATF can also be mixed with other automatic transmission fluids if draining the pan isn’t an option.
Best affordable ATF
Product specifications
Container Size: 1 gal. | Synthetic: Yes | Flash Point: 420 degrees | Pour Point: -65 degrees
This synthetic transmission fluid excels at preventing excessive temperatures from damaging the internal components. We like that it comes in a pack of six 1-quart bottles, making it easy to pour without spilling or handling a large jug.
While it’s great at high temperatures, this ATF can also go low. Mobil claims that it is just as effective in preventing transmission failures at -65 degrees.
Best ATF for high temperatures
Product specifications
Container Size: 1 gal. | Synthetic: Yes | Flash Point: 360 degrees | Pour Point: -32 degrees
This full-synthetic automatic transmission fluid exceeds the requirements of the General Motors Dexron VI specification. Formulated with premium base stocks and additives, the low viscosity enables it to get into every micro space of the transmission.
We found that this greatly reduces wear and tear, lowers the internal temperature and breaks down any sludge that can impact performance. It is available in various container sizes, ranging from a 1-quart bottle to a case of six 1-gallon bottles.
Best ATF for older Ford and GM vehicles
Product specifications
Container Size: 1 gal. | Synthetic: Yes | Flash Point: 350 degrees | Pour Point: -45 degrees
If you drive an older model Ford or GM vehicle, you’ll know that sometimes they require a bit of extra love and care. What goes into the engine and transmission also matters, which is why we think this ATF is the best choice for getting a few more miles out of your truck.
Available in bottles ranging from 1 gallon to 6 gallons, this ATF is licensed by Ford and GM for use in their vehicles. As with other ATFs, it reduces the friction between the metal components, helps to keep the temperature down and ensures smooth gear shifts.
Best ATF for old vehicles
Product specifications
Container Size: 1 gal. | Synthetic: Yes | Flash Point: 356 degrees | Pour Point: -48 degrees
Just as with older vehicles, those with several thousand miles on the odometer are sensitive machines with specialized needs. If you have an automatic transmission vehicle that has 75,000 miles or more on the clock, then this ATF is one of the best to use.
We like that this formula includes additional seal conditioners to prevent leaks, has additional cleaning agents to break down and reduce sludge that hampers performance, and protects against the wear of long-term and frequent gear changes.
It is compatible with all passenger cars and light trucks using Dexron or Mercon automatic transmission fluids.
What is automatic transmission fluid?
ATF needs to do two basic jobs: lubricate bearing surfaces and dissipate heat in vehicles with automatic transmissions. To do these things, ATF needs precise viscosity to suit the transmission concerned. It also needs to be durable — it can’t break down when it gets hot or it’s under extreme pressure.
Different automatic transmissions have different demands. For example, the transmissions on older cars are prone to leaking or accumulating sludge. A specially formulated ATF for older models breaks down the sludge and includes additional sealers to stop leakages. The transmission in a high-performance vehicle will also run hotter than a city sedan or compact and, therefore, must have a higher flash point. Even a reduction of 20 degrees in the fluid temperature can double the life of a transmission.
The manufacturing process of vehicles has changed a lot over the decades, but while that’s generally a good thing, it does create some incompatibilities. For example, many cars made in North America can’t use the same automatic transmission fluids as vehicles from Europe or Asia.
There’s one golden rule with automatic transmission fluid: always buy the grade that the maker of your vehicle recommends. Not doing so can be disastrous, but the task is even more confusing when you flip over a bottle of ATF. Usually, underneath the marketing and ATF highlights, you’ll find which vehicles are compatible with the ATF you are holding. The small print will read something like “Recommended for Vehicles that Require:” and then list several types of vehicle manufacturers’ transmission fluid.
It can’t be stressed enough, but before you buy ATF, double-check what the manufacturer recommends and then check on the back of the label if it’s listed.
Types of automatic transmission fluids
There are two basic types of automatic transmission fluids. Traditional (or regular) automatic transmission fluids are made from natural oils that are combined with antioxidants and corrosion inhibitors. Synthetic automatic transmission fluids are man-made chemical polymers that perform the same functions.
Synthetic ATFs are more durable and resistant to the damaging effects of heat in modern transmissions. As almost all synthetic ATFs are compatible with traditional ATFs (you can mix the two together so long as the synthetic ATF is the same grade), synthetic ATFs are beginning to dominate. However, there are a large number of older vehicles still on the road, and there are specific fluids to suit them.
Traditional ATFs
Type A and Type F are traditional ATFs that haven’t been used in new cars since the 1970s. However, there’s a thriving classic and collectors market out there, so you shouldn’t have any trouble finding appropriate grades of these automatic transmission fluids.
Dexron and Mercon are the most common traditional ATFs. Both are very similar and are used in American and imported vehicles. The big step forward over Types A and F is the addition of friction modifiers — molecules that coat surfaces, thus reducing friction and heat buildup. Dexron and Mercon are the basis for many other ATFs sold under different names.
Synthetic ATFs
Highly Friction Modified (HFM) Fluids are synthetics. They are often, though not exclusively, used in European high-performance vehicles. Popular products ATF+ and 7670 are both HFMs.
Synthetic ATFs closely resemble the properties of Dexron and Mercon. Indeed, there’s a lot of confusion around Mercon V. The name suggests it’s a traditional ATF, but actually, it’s synthetic. This underlines how you must be absolutely sure you get the right grade of automatic transmission fluid for your vehicle.
Choosing the best transmission fluid
While you can mix and match traditional and synthetic ATFs of the same type, you absolutely cannot swap grades.
There are 20 or more variations on the four main types of automatic transmission fluids. Some are specific to a particular automaker — Nissan Matic D, K, J and S, for example. Some are names used by aftermarket brands — Multi-Vehicle ATF, for example. So how do you choose?
For cars manufactured pre-2006 — and particularly classics — you’ll likely have limited choice. For cars manufactured post-2006, you can usually choose from traditional or synthetic automatic transmission fluids. You can buy the vehicle manufacturer’s recommended brand from a local dealer (usually the more expensive option), or you can buy an aftermarket brand online or from a local auto parts dealer.
Whether you choose traditional or synthetic automatic transmission fluid is up to you. The former is often cheaper, while the latter has greater resistance to the effects of heat and friction. For example, synthetic ATF is very popular with those who frequently tow a trailer, which puts additional strain on your vehicle’s transmission.
Automatic transmission fluid vs. manual transmission fluid
Transmission fluid, whether automatic or manual, performs the same job: it lubricates all the metal parts and bearings in the transmission to smoothly shift gears and protects it from overheating. But if it’s the same kind of liquid, what’s the difference and are they interchangeable?
Manual transmission fluid is brown or amber in color and has a higher viscosity. Since automatic transmissions require fluid with a low viscosity, manual fluid will clog up the components, leading to a total shutdown as the internal components have different requirements. Using the wrong fluid causes poor lubrication, increased temperature and mechanical wear.
On the other hand, automatic transmission fluid is usually red or green in color and is a lot more fluid. But unlike manual transmission fluid, you can pour ATF into a manual transmission. In fact, some of the newer manual vehicles today use automatic fluid as it is more effective at lubricating all surfaces, reducing long-term wear.
Best automatic transmission fluid brands
As with almost everything that’s commercially available, there are plenty of brands when it comes to automatic transmission fluid. While it’s always best to follow the recommendations of the vehicle manufacturer, you can opt for a different brand — as long as it’s compatible. Some of the best ATF brands are:
- Valvoline: Founded in 1866 in New York, Valvoline is a global leader in automotive oil, additives and lubricants.
- Castrol: Even if you aren’t mechanically inclined, you’ve undoubtedly heard of Castrol. The British company was founded in 1899 by Charles Wakefield and specializes in greases, lubricants and industrial oils.
- Mobil 1: The synthetic motor oil manufacturer is owned and operated by ExxonMobil, and has a long history in the automotive industry. It has sponsored numerous Formula 1 racing teams and several NASCAR drivers.
Prices for automatic transmission fluids
Automatic transmission fluids generally come in quart or gallon bottles. Quite often, quarts will come in a pack of six. Neither size is necessarily cheaper, but a quart bottle is easier to handle if you’re just topping up. For both traditional and synthetic automatic transmission fluids, you’ll pay somewhere between $20 and $30 a gallon.
Rebuilding a transmission costs thousands of dollars. Buy the automatic transmission fluid your vehicle needs. It’s a small investment that delivers long-term reliability.
Tips
- If you’re buying a used vehicle, ask when the automatic transmission fluid was last changed. Be cautious. It’s common for an unscrupulous seller to put heavy-duty oil in a transmission to disguise problems. Check the color of the automatic transmission fluid using a white rag to see it clearly. It should be pink, red or green (brands vary). If it’s black or brown, it needs changing. If it looks like fresh motor oil, walk away!
- Check your automatic transmission fluid levels regularly. A minor leak can quickly turn into a major mechanical disaster. With automatic transmissions, you’ll often have a dipstick under the hood to make this easy. Be sure you know which is for the transmission and which is for the crankcase (engine oil). Usually, checking is done with the motor running, but have a look in your owner’s manual to make sure.
- Whines, rumbles, struggling to shift gears or popping out of gear are signs of transmission problems. Every mile you drive will only make things worse. If you experience these problems, your transmission needs to be checked immediately.
How did we choose the best automatic transmission fluid?
With so many factors that go into buying automatic transmission fluid, it’s almost impossible to single out one specific brand, type or grade as being the best overall. However, there are elements that make an ATF the best in its class or specific use.
For example, for vehicles with high-performance engines or engines that deliver a lot of torque, the best ATF has a higher flash point and lower pour point than others. For other types, it’s important if there are additives that assist in the smooth running of older transmissions.
However, there are some commonalities that, in general, make for an excellent fluid. For this piece, BestReviews reporter Charlie Fripp compared similar ATFs and looked at the viscosity and stability, heat resistance and operating temperatures, deposit build-up protection, price per gallon, availability and container size.
FAQ
Q. Why do I need to change my automatic transmission fluid?
A. Automatic transmissions run relatively hot compared to manual drivetrains, and that heat eventually breaks down the chemical composition of the fluid. When that happens, it neither cools nor lubricates as well as it should, accelerating wear.
That’s not all. Even the best-maintained transmission wears eventually. Tiny metal particles then contaminate the fluid, which is why it turns a darker color. If these particles aren't removed at the suggested service intervals, they will reduce transmission life and could cause a breakdown.
Q. How often should I change my automatic transmission fluid?
A. It varies from one vehicle to the next, so it’s absolutely vital to check the manufacturer’s recommendations. You’ll find them in your owner’s manual (or online if you don’t have it). Some older vehicles may need fluid changes as frequently as every 30,000 miles, though modern automatic transmissions will run 60,000 to 100,000 miles or more before they need a fluid change.
A new generation of “lifetime fluids” have been designed that never need changing. These synthetic automatic transmission fluids are expected to last the entire vehicle life, so eventually, transmission fluid changes may become a thing of the past. Currently, these ATFs are not common, however, and are only installed in new vehicles.
Q. Is it difficult to change my automatic transmission fluid?
A. It’s not a complex operation — and there are a number of videos online that can help — but it does require patience, and it’s certainly messy.
The biggest challenge is that most automatic transmissions don’t have a drain plug, so the whole pan has to come off to remove the old fluid. It’s a job that has to be done anyway because there’s a filter in there you’ll want to change. You’ll also need a new gasket.
It’s a time-consuming task rather than a difficult one, and doing it yourself will save you a healthy chunk of change. But if you have doubts, you should take your vehicle to a qualified mechanic for an automatic transmission fluid change.
