Which manual transmission fluid is best?
If you drive a stick shift, it’s using a manual transmission fluid to keep things cool and running smoothly. As a result, you can enjoy the feeling of easy, precise gear changes.
But like any lubricant, manual transmission fluid picks up contaminants and eventually needs changing. You can go with what was supplied by the factory, but you might save money and improve performance by choosing another brand. Our quick guide looks at the main considerations, and we’ve made a few suggestions. Ford’s Motorcraft gets the top spot, for its all-around performance, but it’s just one of many quality fluids available.
Types of manual transmission fluid
Early transmission fluid used mineral oils, which were fine on cars of the day. The trouble is, they contain numerous impurities and pollutants like sulfur. They don’t work well at the high temperatures today’s engines generate, and they break down more quickly, reducing their working life. Additionally, mineral oil is a by-product of crude oil and includes numerous solvents, so its environmental credentials are poor.
Synthetic oils are now the standard in both manual and automatic transmissions. Environmentally their detergents, friction modifiers and surfactants probably aren’t any better than mineral oil, but they operate over a wider temperature range, offer increased cooling, and have better stability.
Considerations when choosing manual transmission fluid
The golden rule is that you always go with what the manufacturer of your vehicle recommends. That doesn’t mean you have to stick to a particular brand. There are two figures to take note of: the SAE weight and the GL number.
SAE (Society of Automotive Engineers) weight is the viscosity of the oil, basically how thick it is. You’ll usually see something like SAE 20W50 — the W is for winter because oils are thicker when they’re cooler. So in this case, the manual transmission fluid has a summer weight of 20 and a winter weight of 50. Not so long ago, cans of transmission fluid would be marked with a number like that. Today’s more advanced formulations can take the place of five or six different weights, though it’s still important to check that what your transmission needs is within the range offered.
The GL number is a system created by the American Petroleum Institute (API), and rates transmission fluids by how they react with the various metals used in the gearbox. It runs from GL-1 to GL-5, though GL-4 is far and away the most used. Don’t look at GL numbers as indicating progressively better fluids. In other words, GL-2 is not better than GL-1, it’s just different. For example, GL-5 can actually damage some gearboxes (typically those that use brass components).
Which is more important when selecting a manual transmission fluid? Neither. Both are equally valid. The SAE system has been around longer and is international. Vehicles made outside the USA may not use the GL codes.
Manual transmission fluid price
Prices start at around $12 a quart, and OEM brand fluids can rise to as high as $30 a quart. Bear in mind you’ll need about 9-12 quarts for a full change. Using these figures, the difference between budget and premium brand could be as much as $216, so it’s well worth shopping around.
Manual transmission fluid FAQ
Q. When does the transmission fluid need changing?
A. If you’ve owned the vehicle from new, your owner’s manual should give you recommended mileage between changes. With modern vehicles it’s anywhere from 50,000 miles upwards. If it’s a pre-owned vehicle, then if it looks dirty or contaminated it should be done. If you’re looking at a potential purchase, be aware that fluid that isn’t clear could be hiding gearbox or transmission problems.
Q. Is a manual transmission fluid change difficult?
A. No. If you’re confident with a wrench it should be very straightforward. You’ll need some ramps (never get under a car that’s just on a jack), and something to catch the old fluid in. There are many useful videos online, and a good chance you’ll find one specific to your vehicle.
Manual transmission fluids we recommend
Best of the best
Our take: Ford’s own brand formulation offers long-term protection and performance benefits.
What we like: Wide-ranging model compatibility particularly in older rear-drive, and Zetec-engined models from 1995 onward. Improves shifting at all temperatures.
What we dislike: Expensive, and not all users notice much improvement.
Where to buy: Sold by Amazon
Best bang for your buck
Our take: If you drive a Honda, it’s tough to argue against getting the genuine article.
What we like: An upgraded version of what your car left the factory with. Should improve shifting and reduce wear. Doesn’t carry the price penalty of some OEM fluids.
What we dislike: Honda only. No SAE or GL numbers quoted, and some worry it lacks sufficient viscosity.
Where to buy: Sold by Amazon
Worth checking out
Our take: Low-sulphur formula offers good versatility and reduced environmental impact.
What we like: Synthetic oil that can replace numerous different viscosities, and is popular in European and Japanese vehicles. Safe for synchromesh gearboxes with brass components.
What we dislike: It’s not cheap, and some don’t feel it’s any better than budget brands.
Where to buy: Sold by Amazon
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Bob Beacham writes for BestReviews. BestReviews has helped millions of consumers simplify their purchasing decisions, saving them time and money.
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