Differential Fluid Vs. Transmission Fluid

Most people use the terms differential fluid and transmission fluid interchangeably. But what’s the difference between differential fluid vs. transmission fluid? Well, first of all, just look at their names – they are totally different!

On a more serious note, the fundamental difference between differential fluid and transmission fluid lies in their purpose of being used. Differential fluid has a unique design suited to work with manual gearboxes. On the other hand, their transmission counterparts are most compatible with automatic transmissions.

To get a comprehensive understanding of the differences between these two oils, you need to know about gearboxes and transmissions. While both these do the same thing, control the speed, the way they function is pretty different.

Differential Fluid Vs. Transmission Fluid

For those who are short on time, we’ve amassed the key points in this table. We understand that your time is precious. But if you’re looking to grasp the full idea and have time on your hands, we suggest that you go through the whole article.


Differential Fluid

Transmission Fluid


Differential fluid tends to have a high viscosity because of its need for shock cushioning

Transmission fluid needs to have a certain degree of free flow to be able to lubricate the entire system

Heat Resistance

Between the two fluids, differential oil has a comparatively higher heat resistance

While they have a certain degree of heat resistance, transmission fluid has a lesser amount

Ability to Handle Pressure

Thanks to their high viscosity and some added additives, differential fluid can function well under high pressure

Transmission fluid does not need to handle pressure, so it lacks such properties

Manual Gearbox

Even if you’ve never driven a car before, you may have already guessed it from the name. This type of equipment rests entirely on the driver. Manual gearboxes come equipped with a shifter and a clutch pedal that the driver can use to change the gears manually.

This type of transmission system comprises a pair of shafts paired with a set of gears. And the driver has to use the shifter to set the gear and engage or disengage the pedal clutch.

Automatic Transmissions

Everything that happens within the manual gearbox takes place within the automatic transmission as well. The only difference is that, instead of clutches, the automatic transmission uses a torque converter to change its gears.

While the earlier versions of the automatic transmission did include clutches, they weren’t exactly fully automated. Instead, you could call them semi-automatic.

The gears switch according to the engine’s demand in the automated version. While the gears in a manual gearbox are bigger than automatic ones, the automatic transmission includes more moving parts.

Key Properties of Differential Fluid

The manual gearbox employs a two-shaft system. As such, it generates a lot of heat and friction. As a result, the degree of force produced is comparatively greater.

So, the differential fluid or gear oil has to be able to ensure a smooth operation to prevent any damages to the components involved.

High Viscosity

If you’ve ever seen differential oil, you must have noticed how thick it is. If you compare gear oil vs. engine oil viscosity, gear oil has a much higher density.

In terms of number and ratings, motor oil has a standard viscosity rating of 5W/30. But in contrast, your average gear oil can go around 75 or 90.

This higher viscosity is much needed for the differential fluid to ensure that the entire gear system is lubricated thoroughly. That way, the gears can handle the shock damage and friction that comes from its functionality.

Resistance to Heat

Because of the two-shaft system employed by the manual transmission system, there’s a lot of friction between the components. As a result, the manual gearbox produces a massive amount of heat.

That’s why the gear oil can withstand the higher temperature and transfer the massive amount of heat away from the gear train. And it can do that without vaporizing too quickly, thanks to its higher heat resistance.

Functional Under Extreme Pressure

With a massive number of gears turning all the time, the manual gearbox constantly creates a lot of force. But even in such a condition, the differential fluid maintains its functions properly.

Moreover, some extreme pressure additives can help differential oil withstand even a higher degree of pressure. They help the fluid to maintain its stability and function properly.

Key Properties of Transmission Fluid

The automatic transmission requires a different type of lubrication than the one that differential fluid can provide. So, to ensure proper lubrication and transfer of power, transmission fluid has to have some unique properties than its differential counterpart.

Low Viscosity

Unlike their manual counterparts, automatic transmissions don’t have so much friction inside them. Instead, it has a lot of small parts that need to be adequately lubricated.

To achieve that purpose, transmission fluid has a lower viscosity rating. It’s even lower than motor oil. Manufacturers keep the viscosity of automatic transmission fluid or ATF gear oil around 0W/5 to 5W/10.

That way, the fluid can travel through the whole system and keep each component adequately lubricated. And because of its free flow due to the lower viscosity, the transmission fluid can easily carry the power to the transmission from the engine.

It’s only because of its lower viscous property that the transmission fluid can consistently maintain lubrication throughout the whole system.

Resistance to Heat

Mush like differential oil, transmission fluid also needs resistance to heat. The only difference is the degree of it.

While both fluids act as a cooling agent in their respective systems, manual transmissions produce a lot of heat. So, differential fluids need to have an exceptionally higher heat resistance to take care of that.

On the other hand, there’s not much heat produced in the automatic transmission system due to the lower friction rate. As a result, while the fluid needs a certain degree of heat resistance, it’s comparatively lower than its differential counterpart.

Moreover, transmission fluids require additives to maintain good longevity while withstanding this heat.


Manufacturers equip transmission fluids with anti-foaming technology to prevent air from entering them. That way, the air bubbles can’t interfere in the power transfer process and keep the transmission running smoothly.

Frequently Asked Questions (FAQs)

Can you put transmission fluid in differential?

Yes, you can use transmission fluid for your differential in case of an emergency. For example, if you never change the differential fluid and your gears are going bad, it’s better to take care of the situation with transmission fluid than do nothing.

However, you must remember that there’s a massive difference between the viscosity of transfer case fluid vs. differential fluid. So, it’s not wise to use them in the long term, or you may risk permanent damage.

What happens if I use the wrong fluid?

If you somehow end up using the wrong kind of fluid, be prepared for the world of pain it will cause you. Using the wrong fluid can lead to overheating due to poor lubrication and ultimately end up in transmission failure.

Even with the help of a mechanic, you may not be able to undo the damage. So, try to avoid this mistake at all times.

Can I put engine oil in my differential?

No! No! No! Absolutely not! You should never, ever put engine oil in your differential.

Unlike gear oil, engine oil isn’t designed to sustain high pressure. Instead, it has different strengths that don’t apply to your car’s differential and can put your vehicle at risk.

Can you mix ATF and gear oil?

Mixing different types of fluids isn’t advisable. While you can physically mix them, they may end up harming the machinery rather than doing it any good.

There are different types of fluids and oils available for specific jobs, and it’s best to stick to each particular use case.

Final Words

While most people use the terms differential fluid and transmission fluid interchangeably, it’s better not to mix them up. They both practically serve the same purpose. But they have different designs which play to different types of system’s strengths.

The best rule is to check your owner’s manual and use the recommended one. And if you can’t, just go through the comparison between differential fluid vs. transmission fluid, and you should be good to go!

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