Best Transmission Fluids: Keep Your Car Shifting Smoothly
Our top picks for keeping your car shifting smoothly
The Review Team
How We Decided
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PUBLISHED ON May 8, 2019
Changing your transmission fluid regularly is an important part of keeping your car running smoothly. Taking your vehicle to a professional for this service is usually a lot more expensive than doing it yourself. In this guide, we’ll help you select the best transmission fluid for your needs to help you do the job right.
- Best OverallCastrol Transmax Dex/Merc ATFSummarySummaryEnhanced friction durability makes this ATF our top pick if you’re looking for something that’s (almost) universal and works well in both power steering and transmission environments.ProsProsCompatible with lots of different vehicles requiring Dexron and Mercon; large bottle size; and great price.ConsConsThe labeling is confusing, stating that it’s only compatible with domestic cars. This isn’t the case. It will work with both imports and domestics if your car takes this particular kind of Dex/Merc.
- Best ValueValvoline Dexron/Mercon ATFSummarySummaryA great value buys at almost half the price of our top pick. If you’re looking for something that will give you good performance results while saving you money, this could be the pick for you.ProsProsGreat formulation with easy flow to provide good cold start shifting; minimizes sludge and varnish deposits; works well in custom rigs; and great price.ConsConsAs a mineral-based formulation, it won’t quite match up to the longevity and performance of synthetics.
- Honorable MentionRed Line GL-4 Manual Transmission LubricantSummarySummaryOur top pick for your compatible manual transmission car, this Red Line transmission lubricant delivers results. If you’re looking for something that has a solid performance history, this is the pick for you.ProsProsLess slippery, low sulfur formulation; optimal heat stability; great in high-performance environments; works well in older cars; and has been known to fix third gear issues.ConsConsThe formulation can act up in very cold temperatures, which translates to more difficult shifting for you until the gearbox has warmed up.
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All of our reviews are based on market research, expert input, and practical experience with each product we include. This way, we offer genuine, accurate guides to help you find the best picks.
Benefits of Changing Your Transmission Fluid
- Better fuel economy. Fresh transmission fluid has better resistance to oxidation and meets the lubricating and viscosity standards more easily. These factors can translate into better fuel economy for your car.
- Smoother shifting. When you regularly check and service your car’s transmission fluid, it will result in the smoother movement for your gears. In the long run, it will also protect your gearbox, likely saving you an expensive repair.
- Reduced costs. Changing your own transmission fluid can save you time and money. You can reduce the costs even further by using a synthetic transmission fluid, which has a longer overall lifespan and a couple of other features that make it last longer.
- Extended transmission life. A well-maintained car is one that gets regular transmission fluid top-offs and a complete flush and replenishment when needed. This routine maintenance will help keep your transmission in great working order, and likely extend the life of it in the long run.
- Rust reduction. Transmissions can be pretty finicky when it comes to stuff like rust and corrosion. Moisture, chemicals, and a whole host of other factors can wreak havoc on your transmission, so be sure to change your transmission fluid when recommended to reduce these potential problems.
Types of Transmission Fluid
Originally made for Fords that had bronze clutches, Type F fluid is one that really doesn’t get much use anymore. Bronze clutches haven’t been used since the 1970s, so unless you’re looking for transmission fluid to replenish a classic car or an antique, your vehicle likely has another type.
One of the most common transmission fluids out there, Dexron/Mercon formulations work with most GMs, Fords, and imports. Check your owner’s manual for the official recommendation before assuming this is the fluid you need, though.
Similar to the Dexron/Mercon transmission fluid, HFM fluids provide slightly different friction characteristics that are better suited to some types of transmissions. This fluid is on the market under a couple of different names and is used by a number of imports.
Founded in 1899 in Great Britain, Castrol is a global company priding itself in creating high quality automotive and industrial lubricants. One of the best brands out there, Castrol products are top notch. Some of the best sellers include the company’s Transmax DEX/MERC and the Transmax ATF CVT.
Based in Houston, Texas, Pennzoil has been around since 1913, creating innovative formulations for your automotive needs. As an international oil company, Pennzoil is one of the biggest producers of motor oil, gear oil, and transmission fluid for cars and motorcycles. Popular products include the ATF+4 Transmission Fluid and the 5523 Type-F Transmission Fluid.
With world headquarters in Lexington, Kentucky, Valvoline has a big reach. Producing high-quality automotive lubricants and oils since 1866, Valvoline is a company you can trust. Bestsellers include the DEX/MERC formulation and the DEXRON Full Synthetic transmission fluid.
Transmission Fluid Pricing
- Under $10: You’ll find a wide range of options at this price point. Transmission fluid doesn’t tend to be an expensive product, so you can find quality selections even at this low price point. Keep in mind that some formulations are still better than others.
- $10 - $20: In the mid-range, you’ll find a couple of different types and options, all of which should be good quality. Sometimes it’s worth investing a little extra, especially if you have a newer or more expensive car.
- Above $20: Not too many formulations of transmission fluid are priced here. Usually, you’ll get a bigger container for the higher price, but the quality is about on par with the mid-range, barring a few rare exceptions.
Synthetic vs. Natural
Most transmission fluid types are available in both synthetic and natural forms, with synthetics having the slight upper hand on the market. With their improved resistance to the heat and cold, as well as sheer and oxidation, many manufacturers have already discontinued organic-based compounds in favor of synthetics. Synthetic automatic transmission fluids also tend to last longer, making them the overall recommended choice.
Start by checking your vehicle’s owner’s manual. This will show you exactly which type of transmission fluid you need, so you’re prepared to pick the best one in that class. Keep in mind that most cars use either Dexron or Mercon, but some imports will require brand-specific transmission fluid.
If you have a manual transmission, you’ll need a different transmission fluid than an automatic vehicle would need. Automatic Transmission Fluid (ATF) is more common on the market since most cars are automatic. That being said, Manual Transmission Fluid can be a little bit tricky to find, as it’s closer in composition to motor oil than transmission fluid. In either case, your owner’s manual will help you choose the right fluid type.
- Additives: Some synthetic- and mineral-oil-based transmission fluids also contain additives. While a number of these can be helpful for improving performance and the overall life of both the transmission and the fluid itself, others can be harmful. Monolec is one example of a beneficial additive you can look for.
- Age of Car: A number of older cars will run better on mineral-oil based transmission fluid, and introducing a synthetic ATF could actually lead to damage. If you have an older vehicle, check which fluid it’s been running on, and don’t switch fluid types to ensure the best performance.
- Bottle Size: Depending on your vehicle, it could require 6 or more quarts of transmission fluid for a complete flush and change. Keep that in mind when comparing brands, and opt for multi-packs to save money.
- Quality: Stick with big name brands and respected smaller ones to ensure you’re getting a high-quality product. Knock-offs and cheaper import products might be tempting, but they could end up costing you more money in the long run, for example, if a transmission repair becomes a necessity.
Best Transmission Fluid Reviews & Recommendations 2019
Best Overall: Castrol Transmax Dex/Merc ATF
This Castrol automatic transmission fluid is our top pick. It features enhanced friction durability for smooth shifting and has repeatedly been consumer tested, showing high-performance results. Depending on your exact make and model, Transmax could work for you, as it meets and satisfies the Dexron, Dexron III, Dexron-III H, IIE, and II requirements, as well as all Mercon requirements.
Another use for this ATF is in your power steering if you’ve got a Mercon-requiring vehicle. That makes it an ideal choice if you’re looking to top off your transmission and power steering fluids with one product. The large bottle size is also of benefit since you’ll likely only need one, saving you plastic waste in the process.
As always, make sure to check your vehicle’s owner’s manual to ensure compatibility. The only thing we didn’t like about this particular fluid is confusing labeling. On the label, it mentions that it’s for domestic cars, which is incorrect, since this type of fluid can work in imports as well, so long as they require Dex/Merc fluid.
Best Value: Valvoline Dexron/Mercon ATF
At half the price of other options, this Valvoline ATF is a great value buy. Its performance is considerable, with a couple of great formulation-based qualities. If you live in a colder climate, you’ll love the easy-flow formulation that provides good cold start shifting. Because of this feature, it also minimizes sludge and varnish deposits, keeping your transmission going stronger for longer.
Additives in the formulation protect automatic transmission hardware and transmission seal materials, extending the life of your transmission. In terms of compatibility, it works in place of Ford M2C138-CJ, M2C166-H, Mercon, Dexron, Dexron-II and III, as well as Allison TES-389 transmission fluids. It also works really well for custom rigs and is priced well enough for frequent transmission flushes, in case you’ve got high-performance vehicles that get lots of use.
Since this is a mineral-oil based formulation, it won’t quite match up to the performance of the synthetic variant, but the cheaper price makes it a winner in terms of value. If you’re looking for something synthetic, you might want to check out other Valvoline transmission fluids.
Honorable Mention: Red Line GL-4 Manual Transmission Lubricant
Manual transmissions work a bit differently than automatic ones, which means they also need a different kind of transmission fluid. Red Line’s GL-4 transmission lubricant is our top pick for your manual car (just make sure it meets your specs). The formulation is less slippery and low in sulfur, which makes it compatible with brass synchronizers, and it meets the requirements of 70W, 75W, 80W, SAE 30, 5W30, and 10W30 motor oil. It’s also available in a higher viscosity formulation (MT-85 and MT-90).
With optimal stability at high temperatures and in performance applications, this transmission lubricant does especially well in older muscle cars, as well as sporty Hondas, Dodges, and Acuras. It’s also been known to solve third gear issues in some cars, all while improving the overall glide of the transmission for smooth shifting. Most manual transmission cars require about 2 quarts of fluid, so plan accordingly.
Overall, this is a great quality product with promising performance results. The only problem we noticed in the formulation is that it appears to act up a bit in very cold temperatures. That means more difficult shifting until the gearbox has warmed up enough to thin out the lubricant.
- Check the level of your transmission fluid regularly. If it’s low, don’t forget to top it off to the indicated mark with the recommended fluid type to keep everything running smoothly.
- To properly check your transmission fluid levels, make sure that the engine is warm since this type of fluid expands when hot. Adding a little fluid at a time will help prevent overflowing.
- Changing your transmission fluid DIY-style can get messy. Make sure you have a large enough catch pan to keep the mess off your garage floor.
- About 4 to 6 quarts of new transmission fluid is needed to do a proper change. If you’re doing it yourself, make sure you know how to properly drain and clean all necessary components to avoid damage to your transmission.
- Remember that any transmission fluid change should be accompanied by a new filter and a pan gasket or RTV sealer, depending on your make and model. This will ensure that all components work seamlessly again.
Q: Why do I need to change my car’s transmission fluid?
A: Transmission fluid, like all other fluids in your car, deteriorates in quality over time. The more you use your car, the faster that rate of deterioration will be. In order to keep your car running smoothly, and to avoid a very costly transmission box repair, you should change your transmission fluid.
Q: Can I check if my transmission fluid needs changing?
A: Yes! It’s actually a pretty easy process: Keep your car running for about five minutes, then go ahead and pull out the transmission fluid dipstick and wipe off this first sample on a clean rag. Then, reinsert the dipstick and pull it out again. This time, inspect the appearance of the transmission fluid on the dipstick – if it’s extremely dark or smells burnt, then it’s time to change the fluid.
Q: How often do I need to change my car’s transmission fluid?
A: The timing of transmission fluid change is a bit of a debate. There are no clear-cut guidelines as to when the best time is. Your car’s owner’s manual will have a recommendation on when to do this, but a good rule of thumb is somewhere between 30,000 and 60,000 miles. The rougher you drive your car, the more often a change will be needed.
Q: Can I change the transmission fluid myself?
A: Yes, you definitely can DIY. It’s a little bit more complicated, but doable if you’ve got some tools and a bit of car knowledge. With a little preparation, it’s a task you can complete in an hour or two. Follow these instructions if you’re keen on doing it yourself.
Q: Are transmission fluid and motor oil the same thing?
A: With all the different types of fluids out there, it’s easy to get them all a little mixed up. Transmission fluid and motor oil are not the same things – the former is used to keep your car’s transmission (aka the gears) running smoothly, while the latter makes sure the motor functions well.
Our top pick for the best transmission fluid is the Castrol Transmax Dex/Merc ATF. It works for the majority of domestic cars out there and delivers great results.
If you’re looking for something even more wallet-friendly, check out the Valvoline Dexron/Mercon ATF. It has a great value to performance ratio and can likewise be used in many different makes and models.