Can I use 5W20 instead of 5W30?

In most cases you should not substitute 5W-20 for 5W-30 unless your vehicle’s owner manual explicitly allows it. The engine’s designed lubrication needs, temperature range, and wear protection are tied to the specified viscosity, and using the wrong grade can affect performance and warranty coverage.

Understanding why viscosity matters

Viscosity describes how thick or thin the oil is at different temperatures. The first “5W” indicates cold-start behavior, while the second number (20 vs 30) denotes viscosity at engine operating temperature. A 5W-20 oil is thinner at hot operating temps than a 5W-30 oil. That thinner film can reduce friction and improve fuel economy in some engines, but it may offer less protective film under high heat, heavy loads, or extreme driving conditions.

When you might be able to switch

Some engines are designed to tolerate a 5W-20 oil in place of a 5W-30, typically to meet fuel-economy targets or to accommodate different market specifications. If your owner’s manual or a dealership bulletin explicitly allows this substitution, and the oil you choose meets the required specifications (see below), a switch can be acceptable. If your climate involves frequent hot weather, heavy towing, or sustained high RPMs, sticking with 5W-30 is usually safer.

Before you decide, consider the following criteria to determine if a switch is appropriate for your vehicle:

• The exact viscosity recommended or allowed by the manufacturer for your engine model and year.


• Operating temperature range typical for your climate and driving conditions.


• Warranty requirements and service bulletins from the automaker.


• Oil specification compatibility (API service category and ILSAC grade).


• Engine design factors such as bearing clearances and oil pump pressure that influence required oil film.


• Monitoring options after a switch, including oil pressure and engine temperature feedback.

Conclusion: If the manual explicitly allows 5W-20 and the oil you select meets the required specification, a switch may be acceptable. If there is any doubt, err on the safe side and continue using 5W-30 or consult a certified technician.

How to verify and proceed carefully

To proceed with confidence, follow these steps:

1. Consult the owner's manual or contact the vehicle manufacturer to confirm acceptable viscosities for your engine and market.


2. Choose an oil that meets the exact specification required (for example, API SN plus ILSAC GF-5 or GF-6, and the correct viscosity).


3. If allowed, use the same oil change interval recommended for the current viscosity, and replace the oil filter with each oil change.


4. After switching, monitor for any unusual symptoms such as low oil pressure, engine knocking, or reduced oil temperature control. If such symptoms occur, revert to the recommended viscosity and seek service.

In practice, many modern engines are designed with a specific viscosity in mind to balance efficiency and protection. Always prioritize the manufacturer’s guidance over general advice found online.

Summary

Replacing 5W-30 with 5W-20 is not universally recommended. The decision hinges on the vehicle’s design, climate, and the manufacturer’s approved oil specifications. If the manual allows 5W-20 and the oil meets the required standards, a switch can be acceptable, but always monitor engine behavior and consult a mechanic if you’re unsure. When in doubt, staying with the manufacturer’s recommended viscosity remains the safest course.

Bottom line

Always confirm compatibility with your specific engine before changing viscosity. Your vehicle’s manual and a trusted technician are the best sources to ensure you choose the right oil for long-term engine health.

Is 5W-20 or 5W-30 better for high mileage?

For a high mileage engine, 5W-30 is often recommended over 5W-20, especially if you notice increased oil consumption or noise. While 5W-20 offers better fuel economy, 5W-30's slightly thicker viscosity provides better protection by sealing worn parts and reducing oil consumption in older engines. However, always check your owner's manual first, as some manufacturers specify 5W-20 even for high mileage vehicles, and a mechanic can provide the best advice for your specific engine. 
5W-20 for high mileage 

• Pros: Potentially better fuel efficiency. 
• Cons: Less protection for worn parts and can lead to increased oil burning in older engines. 
• When to use: If your manual explicitly states to use 5W-20, your engine is not showing signs of excessive wear, and you prioritize fuel economy. 

5W-30 for high mileage 

• Pros: Offers better lubrication for older, worn engines, helping to seal gaps and reduce oil consumption. 
• Cons: Slightly less fuel-efficient than 5W-20. 
• When to use: If your engine is high mileage and you are experiencing issues like oil burning or engine noise, or if your manual allows for the switch. Many high-mileage formulas are available in 5W-30. 

Key considerations

• Check your owner's manual: The manufacturer's recommendation is the safest starting point for your specific vehicle. 
• Consult a mechanic: A professional can assess your engine's condition and provide the best recommendation. 
• Consider high-mileage formulas: Regardless of the viscosity, using an oil specifically designed for high-mileage engines can offer additional benefits like seal conditioners and anti-wear additives. 

Does 5W30 burn slower than 5W20?

Yes, 5W-30 oil has a higher viscosity and burns slower than 5W-20 at higher operating temperatures. This is because 5W-30 is thicker at normal operating temperatures, which provides a more robust protective film and reduces the likelihood of the oil breaking down or burning. However, this increased viscosity can lead to slightly decreased fuel economy and increased pressure on the oil pump, so it is important to follow the oil viscosity recommended in your vehicle's owner's manual. 
5W-30 vs. 5W-20

• 5W-20: This oil is thinner at operating temperature, which reduces friction and can improve fuel economy. However, it may break down faster under high heat or heavy loads, leading to higher oil consumption. 
• 5W-30: This oil is thicker at operating temperature, which provides a stronger protective film and can reduce oil burning. This makes it a better choice for older engines or those that experience high heat or heavy-duty use. 

Key considerations

• Fuel economy: Using 5W-30 will likely result in a very slight decrease in fuel economy compared to 5W-20. 
• Engine wear: In older engines or those with worn parts, the thicker 5W-30 can provide better protection. However, in modern engines with very tight tolerances, using a thicker oil can cause the oil pump to work harder and may not lubricate as efficiently. 
• Manufacturer recommendations: Always check your vehicle's owner's manual to see which oil viscosity is recommended. Using an oil with a viscosity that is too different from the recommended grade can have negative consequences, such as decreased fuel efficiency or increased engine wear. 

Can you mix 5W30 and 5W20 synthetic oil?

In nearly all cases, you can use whatever motor oil is available as long as it's clean and from a sealed container. Mixing oils is virtually always better than running on low oil.

Are 5W20 and 5W30 interchangeable on Reddit?

Absolutely nothing bad will happen. If it's a higher mileage vehicle it's actually preferable. Auto manufacturers lean towards the lower viscosity oils as original equipment because it gives them a benefit on the gas mileage calculations.