The Dos and Don'ts of Mixing Different Engine Oils

Is It Safe to Mix Different Engine Oils?

When it comes to maintaining your car's engine, many vehicle owners ask, “Is it ok to mix engine oil brands?” While mixing oils from different brands won't immediately harm your engine, it is not a good idea in the long term. Mixing different brands of engine oil can lead to performance issues, reduced engine protection, and shortened oil change intervals.

Motor oils, whether synthetic or conventional, are specially formulated by oil companies with specific base oils, additive packages, and viscosity grade to meet industry standards. When you mix different types of engine oils, including mineral oil or synthetic blend with conventional motor oil, the resulting mixture may not perform as effectively.

For the best engine performance, stick to one brand of oil—preferably a high-quality option like AMSOIL motor oils. AMSOIL's fully synthetic oils are designed to offer superior protection without the risks associated with mixing oils.

Why Mixing Different Engine Oils Isn't Ideal

1. Base Oil Compatibility Issues

Every motor oil contains a base oil that provides the foundation for lubrication. Oils can be made from crude oil (conventional) or synthetic motor oils, which are lab-engineered for superior stability. The base stocks used in these oils differ in performance characteristics, with synthetic oils offering better high temperature stability, resistance to breakdown, and longer-lasting protection.

The Problem with Mixing Oils

When you combine different brands of oil, you're mixing different types of base oils that may not be compatible. Regular oil (conventional oil) doesn't last as long as synthetic oil and is more susceptible to breakdown. The result is reduced oil's viscosity and poorer engine oil brands performance. The oil may not provide the protection your car's engine needs, especially under high temperatures.

Best Practice: Use High-Quality Synthetic Oils

Stick to one brand of engine oil. AMSOIL's advanced formulations, made from high-quality synthetic motor oils, are engineered for superior durability, offering better protection and efficiency than mixing oils.

2. Additive Package Conflicts

Motor oils also contain additive packages—a mix of detergents, anti-wear agents, friction modifiers, and other components designed to enhance the oil's performance. However, each oil company formulates their oil additives differently, based on their specific standards and formulations.

The Problem with Mixing Additives

Mixing different formulations of motor oil from different brands of motor oil can cause additive incompatibilities. For example, anti-wear additives may become diluted or counteracted, which could reduce protection against wear. Additionally, mixing different viscosities and additive packages can cause sludge buildup or corrosion risks, especially if the oils have unique additives for high-mileage engines.

Best Practice: Use Oils with Balanced Additives

Avoid mixing oils with different additive packages. AMSOIL's motor oils have precisely balanced additives designed for fuel efficiency, high mileage, and long oil change intervals.

3. Impact on Oil Viscosity & High-Temperature Performance

Viscosity is an essential factor in engine oil brands. It determines how well the oil flows in different temperatures. When you mix oils with different viscosity grades—like 5W-30 with 10W-40—you may encounter issues with oil flow.

The Problem with Mixing Different Viscosities

If you mix different viscosities, the oil may flow too thin at high temperatures, reducing protection in high-temperature conditions. Additionally, mixing oils with different weights can cause oil viscosity instability, leading to inadequate lubrication at cold temperatures or excessive thinning when the engine gets hot. This can result in engine wear and the need for more frequent oil changes.

Best Practice: Stick to One Viscosity

Using AMSOIL's high-quality synthetic motor oils, which offer excellent high-temperature and cold-start performance, eliminates the risks of viscosity issues.

4. Sludge Formation & Corrosion Risks

If you combine regular oil and synthetic oil, there is a greater risk of sludge buildup. Oil additives and detergents work together to keep contaminants suspended in the oil. When mixed, these additives may not function optimally, resulting in sludge formation, which can clog oil passages and decrease engine efficiency.

The Problem with Mixing Different Oils

Using conventional motor oil in combination with synthetic blend motor oil may also lead to the weakening of corrosion protection, particularly in older vehicles or high-mileage cars. Sludge formation can reduce the oil's ability to lubricate the engine properly, leading to wear and increased engine stress.

Best Practice: Use Fully Synthetic Oil for Maximum Protection

AMSOIL's fully synthetic oils are formulated to prevent sludge buildup and offer superior high-mileage motor oil performance.

When Is It Okay to Mix Engine Oils?

While it's generally not recommended, there are a few instances when mixing oils may be acceptable:

1. Emergency Situations

If you're in a pinch and your oil level is low, it's better to add a small amount of oil from different brands than to run the engine on used oil. However, this is only a short-term solution. You should replace the oil at the next oil change with the proper oil and brand of oil.

2. Gas Station Oil Top-Offs

If you have to add oil from a gas station that carries name-brand oils, it's acceptable to top off your oil. However, try to stick to your oil formulation and change the oil as soon as possible to maintain optimal protection for your engine.

3. Older Vehicles

In older vehicles with high mileage, mixing synthetic blend oil with conventional oil may be less risky if both oils meet API oil certifications. Always check your vehicle's owner's manual to confirm this.

Best Practices for Engine Oil Maintenance

To ensure your engine performs at its best, follow these tips:

• Use the same brand & formulation – Avoid mixing oils from different companies or formulations.

• Consult your owner's manual – Follow the manufacturer's recommendations for oil type, viscosity grade, and oil change interval.

• Check your oil regularly – Monitor your oil level and keep it at the proper level to prevent unnecessary wear on the engine.

• Stick to high-quality synthetic oils – Use oils like AMSOIL, which are engineered for superior protection, long oil change intervals, and optimal engine performance.

Should You Mix Engine Oil? (Final Verdict)

Mixing different engine oils won't immediately cause damage to your engine, but it can lead to reduced protection and increased wear over time. For the best performance and fuel efficiency, avoid mixing oils and choose a premium synthetic oil like AMSOIL.

AMSOIL motor oils are formulated to protect your engine and ensure optimal performance. With AMSOIL, you won't need to worry about mixing oils and risking your car's performance. Stick to the right oil, based on your vehicle's manufacturer recommendations, and enjoy superior protection and longer oil change intervals.

Get the Best Oil Without the Risk – Choose AMSOIL

Choose AMSOIL for:

• Superior engine protection

• Extended oil change intervals

• Better fuel efficiency

Find the right AMSOIL motor oil for your vehicle using our AMSOIL Product Lookup Guide. If you have any questions, feel free to contact Vyscocity, your trusted AMSOIL dealer.