Can Hydraulic Fluid be Mixed With Transmission Fluid?

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Can hydraulic fluid be mixed with transmission fluid is a common question vehicle owners ask. Often car and tractor drivers think of doing this, expecting a better performance from their vehicle. But should you mix the hydraulic fluid with transmission fluid?

You should not mix the hydraulic fluid with transmission fluid. While hydraulic fluids transmit power, transmission fluid lubricates different mechanical components. Although they both are petrochemicals, they have different additives, making them unsuitable for mixing. If you do, the result can even be disastrous.

But why should you not mix these oils together? What are the key differences between them? Let’s find out answers to all of your questions regarding mixing hydraulic fluid with transmission fluid.

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Is transmission fluid and hydraulic fluid the same?

transmission fluid and hydraulic fluid

The transmission fluid is a liquid that lubricates the transmission system of a vehicle for optimum performance. A transmission system refers to the gearbox of the vehicle that controls the speed and torque.

Hydraulic fluid transmits power within the hydraulic system of a vehicle. It allows the vehicle to do heavy work. Hydraulic fluid can be either water-based or oil-based. 

Transmission fluid is a type of hydraulic fluid, but they are not the same. In general, transmission fluid will include some additives to transmit power that you will not find in the hydraulic fluid, which is basically a lubricant or lubricating agent.

If you are looking for the best transmission fluid and the best hydraulic fluid, you can consider the following options:


Star Fire Premium Lubricants Hydraulic Oil

StarFire Premium Lubricants AW 46 Hydraulic Oil

The StarFire Premium Hydraulic Oil is an oil-based hydraulic fluid that offers excellent wear protection. Plus, the oil has superb resistance power to oil oxidation and rust. It is formulated with premium base stocks that enables it to become more resistant to thermal breakdown.

You will be surprised to know that the StarFire Hydraulic Oil does excellent water separation even at a high temperature. Overall, it’s one of the best hydraulic fluids available in the market right now.


Castrol Transmission Fluid


The Castrol Transmax DEX/MERC Multi-Vehicle Transmission Fluid comes with a low viscosity that offers maximum fuel efficiency and excellent mileage. It provides amazing durability to the friction and allows the transmission system to perform smoothly.

When you are driving on the highway, the temperature of your vehicle’s transmission system increases due to high speed. 

This transmission fluid from Castrol will protect your vehicle in such situations and prevent malfunction. Overall, it’s the best choice for transmission fluids.

Can hydraulic fluid be mixed with transmission fluid?

can hydraulic fluid be mixed with transmission fluid

Both hydraulic and transmission fluids are petrochemicals with some similar characteristics, but they should not be mixed together. 

These oils have their separate jobs. Mixing hydraulic fluid with transmission fluid may have a neutral or disastrous effect based on the types and measurements.

People often tend to mix transmission oil with hydraulic oil to get better performance. If you are thinking the same, you will be disappointed. It’s unlikely that you will get any benefits from the mixture.

Some people may say that there’s no harm in mixing hydraulic fluid with transmission fluid. That can be true when both fluids have similar characteristics, such as the same viscosity, type, additives, pressure rating, etc. Even in this situation, you should not expect any benefits.

However, some of the reasons why it is not recommended to mix different vehicle oils together are:

  • It will compromise the quality of the additives leading to the risk of mechanical wear.
  • Your car or tractor will not perform well due to an inefficient mixture of different fluids.
  • It also can cause a malfunction in the transmission, engine, or hydraulic system.

Considering the above points, there’s no reason to mix these fluids together when you have both oils in your hands. It’s best to use hydraulic oil for the hydraulic system and transmission oil for the transmission system.  Also, keep in mind that none of them are cleaning fluids, so they won’t work similarly to how radiators can be cleaned by JB Weld.

Transmission fluid vs. Hydraulic oil

You already have understood that transmission fluid and hydraulic fluid are not the same. Now, you must be wondering, what is the difference between transmission oil and hydraulic oil?

Let’s have a quick look:

FeaturesTransmission oilHydraulic oil
FunctionLubricates moving partsTransmits power
Working temperatureLowerHigher

You can clearly see there are a lot of differences between hydraulic fluid and transmission oil. These are the main reasons why we don’t recommend mixing them together. It will contaminate the oils and degrade their performance.

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What happens if you mix transmission fluid with oil?

If you mix transmission fluid with oil, it will create a completely different liquid with different characteristics. It will also reduce the effectiveness of the transmission oil. As a consequence, the transmission oil will fail to lubricate the moving parts properly.

Due to the inefficient lubrication, the engine will not be able to transmit the power to the wheels well. Hence, you will not get the best performance from your vehicle.

Can I use transmission fluid for hydraulic fluid?

Can I use transmission fluid for hydraulic fluid

There’s an interesting question among the automobile drivers. Although you can not mix them, can you use transmission fluid as hydraulic fluid?

You can use transmission fluid as hydraulic fluid. It will work fine, but you may not get optimum performance if the working temperature or the PSI of the transmission oil is too low. Besides, you also can use engine oils instead of hydraulic fluid.

However, I won’t recommend using different oils in the hydraulic system. It will most probably degrade the performance of your vehicle. 

This is only an alternative option in the case of an emergency when you do not have access to hydraulic oil. Using a different oil for a short time should not cause any problem.

Alternatively, you may also ask if you can use hydraulic fluid as transmission oil?

Yes, you can do that, too, as the hydraulic fluid has higher working pressure and temperature rating. But the higher viscosity of the hydraulic fluid may cause problems while you use them in the transmission system. Therefore, this is also a solution only for emergencies.

More Questions?

Can you use vegetable oil instead of hydraulic oil?

Although vegetable oil and hydraulic oils have several similar components, using them alternatively is not a good idea. That’s because vegetable oil offers unstable performance in high temperatures. Plus, it also has poor oxidation. 

Can you use brake fluid for hydraulic fluid?

You can not use brake fluid for hydraulic fluid. Brake fluids are not compatible to work with the components in the hydraulic system. They are suitable for use with rubbers. Alternatively, you should never use hydraulic fluid for brake fluid.

Can you mix transmission fluid with oil?

You should not mix transmission fluid with oil. Engine oils have fewer detergents than the transmission fluid. Therefore, if you mix them, it will contaminate the transmission fluid and make it less efficient.

Is compressor oil and hydraulic oil the same?

Compressor oil and hydraulic oil are pretty similar. They don’t have any detergent and share several characteristics, such as high working temperature. Compressor oil can be used alternatively with 20 or 30-weight hydraulic fluid.

Bottom Line

The answer to the question, can hydraulic fluid be mixed with transmission fluid, is you should not. Using the mixture should cause no problem in the short term, but recommended to avoid it. If you are already using a combination of transmission fluid and hydraulic fluid, flush out all the oils and fill the tanks with the fluids they require.

Robert Lozano

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