Can You Mix Synthetic Gear Oil With Regular Gear Oil: 2 Considerations

Gear oil is an essential component for lubricating your vehicle’s gear systems, ensuring that they perform optimally and last longer. Generally, two types of gear oils are available in the market, synthetic and regular gear oil, each with different compositions.

As these two types differ in their synthetic or mineral-based composition, you might wonder whether you can mix regular gear oil with synthetic. According to my research, you can mix synthetic gear oil with regular gear oil if their viscosity and specification are the same.

I will explain what you should consider when mixing synthetic gear oil with regular gear oil and the problems of mixing incompatible oils. So, you can understand the circumstances in which you may use synthetic gear oil in conjunction with regular gear oil to maintain your vehicle’s smooth gear system.

When Can You Mix Synthetic Gear Oil With Regular Gear Oil: 2 Important Considerations

When thinking about mixing synthetic gear oil with regular gear oil, there are two important considerations to keep in mind, which I’ll share below.

• Viscosity and specification matching
• Base stock of synthetic oil

Now, explore each crucial aspect when mixing synthetic and regular gear oil.

1. Viscosity and Specification Matching

To ensure compatibility when combining synthetic gear oil with regular gear oil, you have to consider the matching of viscosity and specifications. For example, if both types of gear oil in your car are 75w90 GL5, they are likely compatible for mixing.

Viscosity refers to the oil’s resistance to flow, and it’s crucial to select oils with similar viscosity grades. This ensures that the lubricant will flow properly and provide adequate protection to the gears.

Additionally, you need to verify that both oils meet the required specifications, such as the API (American Petroleum Institute) rating and the GL (Gear Lubricant) rating. These specifications ensure that the oil has undergone specific testing and meets the necessary performance standards.

2. Base Stock of Synthetic Oil

If you want to mix synthetic gear oil with regular gear oil, you should take into account the base stock of the synthetic oil. Different synthetic oils are formulated with varying base stocks, such as polyalphaolefin (PAO) or polyalkylene glycol (PAG).

PAO-based synthetics are generally more compatible with regular mineral gear oils, while PAG-based synthetics are not, due to their distinct properties. PAO-based synthetics have excellent thermal stability and high viscosity index, making them suitable for blending with mineral gear oils.

However, PAG-based synthetics have different chemical characteristics that may not mix well with mineral gear oils, leading to potential performance issues. Therefore, it’s crucial to verify the base stock of the synthetic oil before attempting to mix it with regular gear oil on your vehicle to avoid any compatibility or performance problems.

What Problems Arise When Mixing Incompatible Synthetic Gear Oil With Regular Gear Oil?

When you mix incompatible synthetic gear oil with conventional gear oil, several problems can arise.

1. Formation of Tar-Like Substances

Mixing unsuitable synthetic gear oil with regular gear oil can lead to the formation of viscous and tar-like substances, which can clog vital components and cause reduced lubrication and increased friction.

When these substances are formed, they can adhere to surfaces within your vehicle’s gear system. This can result in the formation of a sticky residue that hinders the smooth operation of the equipment.

The tar-like substances can accumulate over time and create a barrier that prevents the proper flow of lubricant throughout the gear system. As a result, the equipment may experience decreased lubrication, leading to increased friction and wear on the components.

It’s crucial to avoid mixing incompatible gear oils to prevent the formation of these detrimental substances and maintain optimal gear system performance.

2. Bearing Failure

You can experience bearing failure if you mix incompatible synthetic gear oil with conventional (regular) gear oil in your vehicle or equipment.

When these two types of oil combine, they can form a thick, gummy residue that can interfere with the proper functioning of bearings. This residue can clog the bearings, preventing them from rotating smoothly and causing increased friction and heat.

Over time, the excessive heat and friction can lead to wear and tear on the bearings, ultimately resulting in their failure. When bearings fail, the machinery they support can experience significant damage, leading to costly repairs and extended downtime.

3. Reduced Lubrication Properties

By blending non-compatible synthetic gear oil into regular gear oil, you can significantly reduce the lubrication properties of the resulting mixture.

When these oils aren’t compatible, they may have different viscosities and chemical compositions, which can negatively impact their ability to provide adequate lubrication.

Reduced lubrication properties can lead to increased friction and heat generation within the machinery. This can cause excessive wear and tear on the equipment, leading to premature failure of critical components such as gears, bearings, and shafts.

Additionally, the lack of proper lubrication may result in increased noise, vibration, and inefficient operation of the machinery.

It’s essential to ensure compatibility between different types of oils to maintain optimal lubrication properties and prolong the lifespan of your equipment.

4. Equipment Damage

When synthetic gear oil is mixed with regular gear oil, it can result in equipment damage, leading to costly repairs and extended downtime. When these two types of gear oils are mixed, they can react chemically and form substances that are harmful to the equipment.

Does mixing compatible synthetic gear oil with regular gear oil impact your car’s performance?

You can expect a minimal impact on your car’s performance when combining compatible synthetic and regular gear oil.

As long as the oils are compatible and meet the necessary viscosity and specification requirements, the resulting blend will provide effective lubrication. This blend will also offer protection for your vehicle’s components.

Additionally, it’s essential to consider gear oil expiration and ensure that the oils are within their usable shelf life. As a result, the performance of your car shouldn’t be significantly affected when using a well-matched combination of synthetic and regular gear oils.

How do you verify the GL5 rating of gear oil when considering mixing synthetic with regular gear oil?

To verify the GL5 rating of gear oil prior to mixing synthetic with regular gear oil, start by examining the product label or specification sheet. 

Look for the API classification, specifically ‘API GL-5.’ This classification is provided by the American Petroleum Institute (API) and is designed for high-speed and high-load conditions in automotive axles, particularly for hypoid gears.

It’s important to consult your owner’s manual as well, as it will outline the manufacturer’s recommended viscosity and specifications for your specific application. Typically, these recommendations fall within the API GL-4 or GL-5 range.

Adhering to these guidelines ensures that you’re using the appropriate gear oil, whether synthetic or regular and helps prevent any potential issues that may arise from mixing incompatible oils.

Mix Compatible Gear Oils for Optimal Performance and Protection

It’s clear that you can mix synthetic gear oil with regular oil if they are compatible and have matching viscosity and specifications. This practice can maintain a smooth gear system in your vehicle while providing adequate lubrication and protection for its components.

You have to be cautious and avoid mixing incompatible oils, as it can lead to the formation of harmful substances, bearing failure, reduced lubrication, and equipment damage.

However, based on my research and opinion, using synthetic or regular gear oil separately remains a reliable choice for preserving your vehicle’s gear system. Mixing synthetic gear oil with regular gear oil should only be considered a last resort when no other suitable options are available.