Can Engine Oil Mix With Transmission Fluid? Learn More

Let’s start by saying that, engine oil and automatic transmission fluid are designed differently, so mixing the two together is not recommended.

You should refrain from mixing engine oil and transmission fluid as it may disrupt the balance of combustion, leading to misfires, reduced speed, and other potentially hazardous results.

In this post, we will be explaining whether or not it is safe to actually mix engine oil with transmission fluid. So, continue reading to learn more in regards to this topic.

Can Engine Oil Mix With Transmission Fluid?

Can Engine Oil Mix With Transmission Fluid

Engine oil and transmission fluid are two distinct lubricants designed for different tasks. The oil acts as a lubricant in the internal combustion system of a car, while the ATF fluid ensures clutches and gears run smoothly within the transmission.

Both fluids are designed with base oils to prevent contamination, reduce friction, dissolve gunk and provide a protective layer against corrosion. Apart from that they also contain additives which lubricate gears, prevent wear, and guarantee proper operation.

However, mixing these two fluids is never recommended as they are intended for different parts of the vehicle. Doing so could result in poor lubrication, overheating and transmission failure.

Another reason why it’s not a good idea to mix transmission fluid with engine oil is that this mixture will make the fluid thicker, decreasing its flowability. Simply mixing them could increase the likelihood of sludge accumulation in your crankcase.

It has been a widespread mistake for decades, though it is becoming less frequent. Many mechanics are even warning against mixing transmission fluid and engine oil as it will decrease its solvency, leading to misfires, decreased speed, and an imbalance in combustion process.

Learn More: Can You Mix Engine Oils in Your Car

Difference Between Transmission Fluid and Engine Oil

First and foremost, their purposes, appearances, functions and properties differ considerably. Not only that but they even contain different base oils and additives.

Another key distinction is that engine oil lubricates and cools the internal combustion engine, while transmission fluid does the opposite; it helps protect metal parts from overheating, deterioration and damage.

It is safe to say that motor oil has a higher viscosity than transmission fluid, which can negatively impact the performance of your car’s gears and clutches. Additionally, this may cause harsh shifting when shifting gears or clutches.

When Can You Put Transmission Fluid in the Oil?

Transmission fluid is a thin, slippery liquid that coats and cools the transmission’s moving parts. It travels between them via pumps, valves and an internal computer that regulates fluid amounts throughout the transmission.

Due to this, it’s virtually impossible for someone to accidentally put transmission fluid into your engine unless a mechanic makes an error. Fortunately, this scenario occurs only rarely.

However, mixing these fluids can have disastrous results for your vehicle’s performance. Thus, it’s essential to understand how and when these two fluids should be combined.

Mixing transmission fluid with your engine oil is possible and should only be done when you are flushing engine from engine sludge, but it’s best to avoid adding too much. Doing so will significantly alter the base oil in your motor oil, potentially leading to severe engine damage.


There are lots of people who actually wonder to themselves whether it would be safe to mix engine oil with transmission fluid. Well, as you can see, it is not a good idea to do so and we only recommend mixing them together if you are planning on flushing your engine from sludge and when doing so you should only mix a small amount just for safety reasons.