When talking about electric cars, people sometimes ask if the transmission fluid needs changing - or even if the EV has transmission fluid or a transmission mechanism, hence this article aims to clear up this confusion.

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Recap of Transmissions/Transmission Fluid

Before looking at EVs, we’ll briefly recap on the purpose of transmissions/gears in a conventional, gasoline-fuelled car. The transmission’s job in a moving system is to ensure that the correct amount of power is applied to the wheels, to ensure that the ‘desired’ speed is achieved. Conventional cars and multi-gear bicycles are similar in this sense: they both have gears, which need to be set correctly (low gear when starting off; higher gear when travelling at higher speeds) to ensure continued movement.

Transmission/gearing mechanism from a conventional car, via FreeImages

However gears can’t simply be changed to another gear: since it’s a mechanical operation, a ‘disconnect’ is needed before the gear can be changed up or down. With a bicycle, this is done via the chain operation. Whilst with a gasoline car, the transmission is the thing that provides the necessary disconnect with the engine to allow for the gear to be shifted upwards or downwards.

In a manual car, the clutch is the thing that allows you to ‘disconnect’ and change gear. In an automatic car, there’s an automatic transmission/gear shifter system which detects when a gear needs to change and applies this disconnect and change automatically.

Because this is a mechanical operation (aka there’s various moving parts), transmission fluid is needed to keep all the parts working together smoothly: transmission fluid is a slippery lubricant liquid. It also helps to cool things down, acting as a heat dissipator. It usually needs changing every 30,000 miles or so in a conventional car.

Torque and Single-Gear EVs

So as we mentioned above, the transmission is designed to ultimately turn the wheels. This is done by applying torque (rotational ‘movement’ energy). In conventional ICE cars, the ICE only generates usable torque in a fairly narrow band of RPM (engine ‘spin’ speed). Hence to keep things efficient, ICE (aka gasoline) cars have multiple gears which allow the engine to spin at the most ideal RPM range for the most ideal torque to be applied.

This is entirely different with electric cars. They have high-RPM electric motors which can apply the necessary torque in a much more fine-grained, consistent approach across RPM levels. As a result, an electric car only needs a single gear to function (unlike the ‘fussier’ ICEs which require gears to deliver the best torque). If you’re interested in the maths behind this, a great video is:

Transmission/Transmission Fluid in EVs

As explained above, EVs only have/need a single-gear. As a result of this, a transmission system is not needed in an electric car. Instead, an EV will just have a fixed-ratio gearbox which aims to strike the right balance between acceleration and the top-speed.

And since there’s no transmission, there’s no transmission fluid required in an EV either! This is one of the nice benefits of an electric car: there’s less maintenance work (hence cost) required, due to needing less oil and fluid changes.

… but my friend just had his Tesla Model S’ transmission fluid changed?

On a final note, you might have heard that the Tesla Model S does need transmission fluid changed. In general, everything said above is true and the transmission fluid doesn’t really need changing in an EV.

However there’s a little bit of confusion with Telsa because the Model S contains a form of gearbox which contains transmission fluid, hence the Tesla service checklist PDF says that the transmission fluid needs changing at the 12 year - or 150k mile - mark. And some people on the Tesla forums have even said they’ve been advised to change the transmission fluid at the 1 year - or 12.5k mile - mark instead.

So it’s a little unclear, but our advice is to not change the transmission fluid on your Model S, unless specifically told by your dealer. If your EV has low mileage and no handling issues which might be drivetrain related, the car’s transmission fluid is almost certainly fine.