What happens if you put transmission fluid in the oil?

Transmission fluid and engine oil are both important for different components of your car. However, given that they are both solvent lubricants, you might wonder what would happen if transmission fluid were added to the oil.   

While they both may be fluids made for your car to run, they have different purposes. And combining them may end up working against you! To learn more, keep reading! 

What Happens If You Put Transmission Fluid in The Oil?

If you mix around 1 quart of automatic transmission fluid with engine oil, it can help remove stubborn engine sludge. Some also use this mixer to flush the engine. However, you shouldn’t use too much since transmission fluid can harm your engine! 

Transmission fluid is not a substitute for engine oil. Engine oil is not only a lubricant but also works as a solvent for the engine. 

The engine develops engine sludge and contaminants from the burning gas. and engine oil helps control and dissolve them. The oil is later changed and refilled. 

On the other hand, transmission fluid can sometimes be used as a tool to remove sludge when mixed with engine oil. 

But the fluid needs to be ATF, or automatic transmission fluid, and not manual transmission fluid. This is because ATF is made out of naphthenic-based oil with a high solvency level. 

Also, if you want to put transmission oil in fluid, do not use it to run your car! The transmission oil will affect the balance in combustion, which can lead to dangerous outcomes. 

What is the Difference Between Transmission Fluid and Engine Oil?

To better understand the difference between transmission fluid and engine oil, you need to know them separately. So, here is a short description of both transmission fluid and engine oil: 

1. Transmission Fluid 

Transmission fluid is used to lubricate and help the transmission system run smoothly. Without the fluid, the transmission system will not be able to function properly. 

For this reason, transmission fluid usually stays in a car for a long time and is not refilled often. The fluid also helps keep the transmission system fresh and prevents harmful contaminants. 

2. Engine Oil 

On the other hand, engine oil is also a lubricant! But it’s made for the internal combustion system of your car’s engine. It prevents contaminants, reduces friction, helps dissolve engine sludge over time, and prevents wear in the engine. 

The thickness of the oil is also an important factor. If too thick or thin, the oil will not be able to work properly, causing misfires and other engine problems. 

The Difference 

The biggest difference between transmission fluid and engine oil is their functionality. Here is a more detailed explanation: 

Difference 1 : 

  • Engine oil works for a car’s combustion system. 
  • Transmission fluid works for the transmission system of a car.

Difference 2 : 

  • Engine oil helps the combustion system run swiftly, wear protection, and contaminants protection.
  • Transmission fluid helps the transmission system run smoothly and stay lubricated. 

Difference 3 :

  • Engine oil is changed and refilled. 
  • Transmission fluid is not changed unless expired. 

It’s safe to say you can’t use one as the other’s substitute. But as mentioned before, automatic transmission oil is sometimes mixed with engine oil for sludge cleaning. But be careful of the side effects while using this trick! 

Here is a video showing the differences between transmission fluid and oil: 

When Can You Put Transmission Fluid in The Oil?

You can put transmission fluid in the engine oil while flushing your engine for engine sludge. But, you have to make sure the transmission fluid used for this process is an automatic or ATF blend. 

Automatic transmission fluid has a much higher level of solvency, which helps dissolve stubborn engine sludge. Add one quart of ATF in your oil and give your engine 2-3 flushes before refilling the oil! 

It may or may not improve the cleaning process, as most engine oils nowadays are quite capable on their own. Also, using ATF in the engine oil will decrease the engine oil’s solvency and lubrication. So, it’s better not to mix these two fluids. 

Is it bad to put transmission fluid in the oil?

Many believe automatic transmission fluid in your oil can help enhance solvency, but this theory is quite backdated. 

Back in the days when engine oil wasn’t as good in terms of solvency, the trick of mixing ATF worked wonders! 

But along with it came a set of new problems such as engine wear, decreased speed, misfires, an imbalance in the combustion system, etc. 

The reason for this is ATF doesn’t have the same protection properties as engine oil does. 

And in today’s times, engine oils have a much better level of solvency, and using the transmission fluid trick is mostly a waste of time. 

On top of that, running your car while using it is highly dangerous! This is because transmission fluid doesn’t have the same level of contaminant control. 

The burning gases in the combustion system mainly release these contaminants. Additionally, they have the potential to blow the engine out if improperly managed. 

How To Use Transmission Fluid in the Oil to Flush Your Car?

You can use automatic transmission fluid to flush your car. But, if done wrong, you might end up ruining the engine! So, here is how to use transmission fluid in the oil to flush your car: 

  • Put 1 quart of automatic transmission fluid in the oil can
  • Add the mix to the engine
  • Run the engine for about 50 miles in idle 
  • Flush out the mix 
  • Repeat the process 2 more times 

Frequently Asked Questions

Now, it’s time to answer some common questions people have regarding this topic! These questions will give you an overall understanding of what happens when you put transmission fluid in the oil. 

Is engine oil better than transmission fluid?

Engine oil is not better or worse than transmission fluid. The engine oil is made for the internal combustion system, not the transmission system! So, depending on the purpose, it can be better. 

Will transmission fluid in engine oil damage the engine? 

Using transmission fluid in the oil will affect the engine oil’s ability to keep the car’s engine lubricated. Transmission fluid will overall cause an imbalance in the engine oil, which will damage the engine.  

Are engine oil and automatic transmission fluid the same thing?

No! Transmission fluid is mainly a hydraulic fluid, while engine oil is a lubricant for the engine of a car. While ATF is known to have many adhesives similar to engine oil, the purpose and effects are different. 


There you have it. When it comes to mixing two different types of fluid, you can do it to a certain extent. But remember, these two lubricants are made for different purposes. Therefore, it is better if you avoid mixing these two oils together. 

Similar Posts