Can I Use Motor Oil For Transmission Fluids?

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Motor oil and transmission fluid are similar lubricants used in the automotive industry. There are mainly two types of transmission fluids, and they are automatic and manual transmission fluids. If you have extra motor oil, you may think can I use motor oil for the transmission system?

These two fluids have specific similar characteristics, and their base oils are also very similar. So we should know the similarities and differences between these two lubricants before use.

In this article, we will discuss; whether can I use motor oil for transmission fluid. What happens if you put motor oil in the transmission? Difference between these two fluids and much more.

Can I Use Motor Oil For Transmission Fluids

What Is Motor Oil?

Motor oil, AKA engine oil, is a lubricant that uses an internal combustion engine to lubricate moving metal parts. This fluid is made of either crude oil or synthetic oil with various additives to prevent wear, and corrosion, reduce friction, clean deposits, improve fuel efficiency, provide protection in a wide range of temperatures, and much more. There are several categories of motor oils on the market. These oils contain many performance-enhancing additives including, anti-wear, anti-foam, dispersants, detergents, extreme pressure (EP), friction modifiers, antioxidants, corrosion inhibitors, viscosity index improvers, and pour point depressants.


What Is Transmission Fluid?

Transmission fluids use in the gear system for smooth shifting, maximizing transmission performance, reduced wear, and much more. Transmission fluid, AKA gear oil, is a kind of hydraulic oil that lubricates, and there are mainly three types of fluids. They are automatic transmission fluids, manual transmission fluids, and CVT fluids. All these types of fluids are made of either synthetic or petroleum base fluids with performance-enhancing additives. Synthetic fluids are produced a chemical reaction of various base oils, have excellent withstand at high temperatures, and perform better than regular transmission fluids. Some additives are anti-wear, anti-rust, corrosion inhibitors, detergents, dispersants, viscosity improvers, and extreme pressure additives.



Can I Use Motor Oil For Transmission Fluids?

No. You cannot use motor oil for the transmission system. These two fluids have some similar properties but are not interchangeable. Transmission oil is not the same as engine oil. Using engine oil in the automatic or manual transmission system can damage the gear system, cause problems shifting gears, and lead to costly repairs. Motor oils are thicker than transmission fluids and can clog up the system.

Using motor oil for transmission fluid will reduce clutches and gear-shifting performance, decaying rubber parts. Also, it is difficult to tell if the transmission fluid needs to be changed by checking the fluid color change (brown/dark brown).



What happens if you put motor oil in the transmission?

A small amount of motor oil in the transmission may not cause any problems. If you mix motor oil with transmission fluid, you must flush the lubricant and refill the manufacturer-recommended lubricant. Flushing and filling the gear oil is not challenging, and changing the transmission oil filter is recommended. The possible malfunctions of using motor oil as a transmission fluid can be summarized as follows;

  • Damage rubber parts like gaskets and O rings: The gear system contain several rubber parts, and when using thicker oil, it can damage or leak oils from these parts.
  • Grinding or shaking movements when changing gears. Using motor oil for transmission fluid can damage internal rubber parts. This can result in unusual sounds and shaking when shifting gears.
  • Gear shifting delay: The system responds slowly due to the thicker oil.
  • Poor lubrication: Wrong fluids do not provide enough lubricant film on metal parts. So it can increase metal wearing.
  • Overheating: The correct viscosity fluids maintain the system temperature. So motor oil can cause overheating gear system.
  • Slipping Gears. You may experience a sudden downshift or shift to a higher gear.
  • Possibly transmission failure.



What is the difference Between Motor Oil And Transmission Fluid?

The main difference between motor oil and transmission fluid is viscosity. Generally, transmission fluids are less viscous than engine oil. Other differences are motor oil contains less detergent and dispensers.

ParameterMotor OilTransmission Fluid
Viscosity @ 40°C (104°F).Over 40.Between 30 to 40.
AdditivesLess detergent and dispenser. More detergent and dispenser.
Base oilCrude oil, synthetic oil.Crude oil, synthetic oil.
Viscous levelThicker.Thinner.



How do flush transmission fluids?

If you use motor oil or mix a considerable amount of motor oil in the transmission system, you must flush out the contaminated oil and clean the filter. This flushing fluid ensures that your transmission system works correctly and is trouble-free for a long time. A small amount may not cause significant damage.

  • First, park the vehicle in the proper location.
  • Using a hydraulic jack/floor jack or ramps to lift the vehicle.
  • Remove the drain pan carefully. Usually, this oil pan is connected using bolt nuts, and while removing the nuts, the oil may leak. Take necessary precautions to prevent oil spillage.
  • You can see oils flowing down when removing half of the bolts and tilting. Carefully collect them in a pan.
  • Remove the oil filter carefully and connect the new one.
  • Remove the oil pan gasket carefully. Then clean the oil pan using brake cleaner and a hand Pad. This will remove the remaining oil residue, grime, and gasket materials.
  • Wait a few minutes to dry the pan.
  • Apply silicon paste on the gasket and apply it carefully. This will stick it with the pan.
  • Install the transmission fluid pan using bolts.
  • Now you can fill the new transmission fluids. Using a funnel, fill in the recommended fluid. Once done, clean the dipstick too.




Is transmission oil the same as engine oil?

No. Transmission oil is not the same as engine oil. Engine oils are more viscous lubricants. Furthermore, engine oil is exclusively developed for lubricating internal combustion engines. Generally, transmission fluids viscosity (mm²/s) at 40°C (104°F) is 30 to 40 range. However, motor oils’ viscosity (mm²/s) at 40°C (104°F) is over 40.



It is not recommended to use motor oil for transmission fluid. Motor oils are thicker, and transmission fluid is a lighter oil. Using more dense oil in the gear system can cause problems like slow gear shifting, shaking movements, and damage to rubber parts like gaskets and O rings.

If your car is still under warranty, you should only use the manufacturer’s (OEM) recommended oil. Use of any other oil will void the warranty.

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