What happens if I mix transmission oil with engine oil?

When it comes to car maintenance, oil is a key component for the proper functioning of the engine and transmission. But what happens if you mistakenly mix transmission oil with engine oil? Or worse, if you try to use one instead of the other?

In this SUN Transmissions blog, we'll explore the differences between the two, their functions and the consequences of mixing or using them incorrectly.

Differences between engine oil and transmission oil

Although both are lubricating oils, engine oil and transmission oil have very different compositions and functions:

Engine Oil

Engine oil is designed to lubricate and protect internal engine parts against friction, heat and residues generated by combustion. Among its main characteristics are:

• Formulated with detergent additives to keep the engine clean.
• Designed to resist high temperatures.
• Contains viscosity modifiers to adapt to different operating temperatures.
• Protects against corrosion and oxidation.
  

Transmission Oil

This oil is used in automatic or manual transmission, facilitating gear shifting and reducing friction in gears and mechanical components. Its features include:

• Extreme pressure additives to protect gears and bearings.
• Increased resistance to shear.
• Lower viscosity in some cases, especially in automatic transmissions.
• Anti-friction and anti-wear properties.
  

What happens if I mix transmission oil with engine oil?

If by mistake you mix transmission oil with engine oil, the consequences can be serious depending on the amount:

Small amount (less than 5%)

In small doses, transmission oil in the engine may not cause an immediate problem, but it is not recommended. It can alter viscosity and affect the engine oil's ability to protect against friction and heat.

Significant amount (10% or more)

Transmission oil does not have the same detergent additives and thermal resistance as engine oil. When mixed in a considerable amount, it could:

• Affect lubrication and cause premature wear on internal engine parts.
• Increase sludge and deposit formation.
• Reduce the oil's ability to dissipate heat, which could lead to engine overheating.
• Alter oil pressure, affecting engine performance.

What if I use engine oil in the transmission?

Although some older manual transmissions used engine oil, as Isuzu did in its Trooper model, which used 15w-40 oil, and some tractors do nowadays.

Today, modern transmissions require specific fluids. If you introduce engine oil into an automatic transmission, it could:

• Affect the operation of clutches and hydraulic components. Resulting in problems when shifting gears, you will notice that the engine over accelerates, but you will not be able to shift.
• Causing slippage when shifting gears. Slipping or feeling the transmission “kick” before upshifting.
  
• Causing overheating and premature wear. Each formulation has specifications that go according to the demands to which it will be subjected, in that sense, a transmission fluid has been designed to protect from overheating when the gearbox is working and is demanded.
  
• Cause total transmission failure. Over time, your vehicle may not be able to move forward because it can't even make a gear change.

In case of any problem in your transmission, find the spare part with us

If you accidentally add a small amount of transmission oil to the engine, it’s best to change the oil as soon as possible to prevent any potential damage. However, if you mistakenly add engine oil to the transmission—or a large amount of transmission oil to the engine—you could face costly repairs.

At SUN Transmissions, find the right transmission oil to use in your vehicle, as well as repair kits, sensors and electrical components for automatic transmissions.

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