Is It Safe To Flush Engine With Transmission Fluid?

Over time, your engine will accumulate many contaminant build-ups that can affect performance. Getting rid of this build-up effectively has been a major contention in the automotive world. One way to achieve this is by using transmission fluid to clean engine sludgeor build-up

Automatic transmission fluid contains a detergent that is perfect for cleaning deposits in the engine, especially deposition left from the use of oil.

However, the problem with using ATF is that it is not designed for that purpose. There are more suitable products that can help you flush your engine.

This article will examine the use, safety, impact and effect of using atf to flush your engine. We will also take a look at how to flush engine with transmission fluid.

transmission fluid to clean engine sludge

Is It Okay To Flush Engine With Transmission Fluid?

An automatic transmission fluid has many additives, giving the fluid a great cleaning ability. The fluids can clean sludge formed in the engine from the prolonged or extreme use of motor oil. However, transmission oil is not completely safe to flush your engine.

Transmission fluid can affect the condition of the motor oil when they come in contact. Transmission fluid is designed to have lesser lubricating power and also includes a much different component to motor oil.

When transmission fluid comes in contact with coolant or motor oil, it could dilute major components of the oil and make it less effective. It majorly happens when too much transmission fluid is poured into the engine.

However, using transmission fluid to flush your engine is not entirely dangerous. If you are going to use transmission fluid, you need the proper procedure to do so. By following the right procedure, you can get an exact amount of transmission fluid for the flushing process.

How Do You Flush Engine With Transmission Fluid?

You need the proper procedure to flush your engine using transmission fluid to prevent engine problems.  It must be done with care and accuracy when adding automatic transmission fluid to oil. Also, the mixture of transmission fluid in oilin the engine must be drained properly.

Below is an easy-to-follow procedure on how to flush the engine using transmission fluid:

1. The first step is draining the old oil in your vehicle. You can do this by locating the drain plug. The drain is usually located beneath the vehicle and is sometimes protected by a covering. You can consult your vehicle manual to locate the drain plug properly.

2. Once you find the drain plug, place a drain pan underneath, unplug, and let the old oil drain. 

3. Change the oil filter once you have drained the oil out of the vehicle.

4. Put in a new oil filter and pour one quart of transmission fluid in engine oil reservoir. Ensure that when you put transmission fluid in car, it is a new standard motor oil. You do not need synthetic oil at this stage.

5. Start the engine and let it idle for about 15 minutes, then turn it off and let it cool down completely.

6. Once the engine has completely cooled down, you can drain the mixed fluid just like you drained the old oil.

7. Remove the old oil filter and install a new one, then fill it with new synthetic oil.

Once you can successfully flush your engine using this procedure, you do not need to worry about transmission fluid in oilthat you put in the engine after the flushing process.

Does Transmission Fluid Clean Engine Sludge?

Yes, transmission fluid can clean your engine from sludge. It contains additives designed to clean sludge, gunk and other deposits. Although it is a good option to remove sludge and other deposits in the engine, it is best to use specific cleaning fluid for your engine.

engine flush with atf YouTube

Can A Transmission Flush Damage A Car?

Using transmission fluid can be dangerous to your vehicle when carrying out the flushing process. If you do not carry out the process as it should, it could affect the new oil put into the vehicle and the engine’s performance.

Below are some reasons transmission fluid might not be the best option to flush your engine.

1. Transmission fluid in oil reduces cleaning power

When flushing your engine with transmission fluid, it makes contact with motor oil. If this happens, it could reduce the cleaning power of the fluid. The reason for this is because the detergent in the ATF is lesser in motor oil. In most cases, the cleaning power of ATF is diluted and less effective when in contact with motor oil.

2. Reduced wear protection when oil comes in contact with Transmission fluid

When you put ATF in engine oil during the engine flushing, it could affect the wear protection the oil provides. Motor oil is made of base oil and other additives, which aids in fighting wear in moving parts, reducing friction and dissolving sludge.

When a motor comes in contact with other foreign substances like ATF, it could affect these additives. Atf will affect the lubricating power of the motor oil, and wear and friction will increase.

3. Change in Oil viscosity

Using transmission fluid to flush your engine could affect the oil’s viscosity. Viscosity is the level of motor oil’s thickness in response to the temperature it is exposed to. When transmission fluid gets in contact with the motor oil, it could either increase or reduce the oil viscosity.

All these factors will occur when the transmission fluid is not mixed with oil properly, and the flushing or cleaning process is not done adequately. The residue of the transmission fluid could remain in the oil reservoir. It could affect the condition of the new oil put into the vehicle, affecting the engine’s performance.


Using transmission fluid to flush your engine is harmless if you follow the proper procedure. You need to ensure that the used transmission fluid is not too much in the engine. You only need a quart of transmission fluid to get the process done. Also, it is best to use Automatic Transmission Fluid (ATF) because it has the needed additives to clean the engine of sludge and other deposits.

Akindayini Temiloluwa

I am Akindayini Temiloluwa, an automotive expert writer and car enthusiast. I have over three years of experience in the automotive writing niche and have completed over 300 pieces of content from 50 projects. I have vast knowledge and skill in vehicle repairing, all mechanical work, car upgrades and maintenance. My goal as an automotive content writer is to simplify the most challenging concepts for my readers, help them self-diagnose what may be wrong with their vehicles and offer real value for their time.

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