Mix 5W20 And 0W20

ByRobert Lozano

In a pinch, yes, you can mix 5W-20 and 0W-20 oil. Since they share the same operating viscosity (the “20”) and are typically modern synthetic oils, they are compatible for a top-off. However, doing so will slightly reduce the cold-start performance of the 0W-20, so it should be considered a temporary solution, not a long-term strategy.

You’re standing in your garage, one-quart low on oil. Your car’s manual clearly calls for 0W-20, but all you have on the shelf is a fresh bottle of 5W-20. The auto parts store is closed, and you have to leave early in the morning. That familiar feeling of uncertainty creeps in—can you even do this?

It’s a common question that sends many DIYers down a rabbit hole of confusing forum posts and conflicting advice. The fear of causing engine damage is real, and the numbers on the bottle can feel like a complex code.

This guide is your clear, no-nonsense answer. We’ll cut through the noise and give you the expert take on whether you can mix 5w20 and 0w20, when it’s safe, and what you need to know to protect your engine. Let’s get you back on the road with confidence.

Understanding the Numbers: What Do 0W-20 and 5W-20 Actually Mean?

Before we dive into mixing, let’s decode what those numbers on the oil bottle actually represent. This isn’t just trivia; it’s the foundation for making an informed decision. The Society of Automotive Engineers (SAE) created this grading system to tell us about an oil’s viscosity, or its resistance to flow.

The “W” Number: Cold Weather Performance

The first number followed by a “W” (which stands for Winter) tells you how the oil flows when it’s cold. Think of it as the oil’s winter coat.

A lower number is better for cold starts. 0W oil flows more easily at low temperatures than 5W oil. This means on a frosty morning, 0W-20 will circulate and protect your engine’s vital components faster than 5W-20.

The “20” Number: Operating Temperature Viscosity

The second number—in this case, “20”—indicates the oil’s viscosity when your engine is at its normal operating temperature (around 212°F or 100°C).

This is the key to our mixing question. Both 0W-20 and 5W-20 are engineered to have the same flow characteristics once your engine is warmed up. They provide an identical level of protection when you’re cruising down the highway.

The Compatibility Factor: Synthetic vs. Conventional

Modern 0W-20 and 5W-20 oils are almost exclusively synthetic or synthetic blends. A huge benefit of these advanced formulas is their miscibility. As long as both oils meet the current API (American Petroleum Institute) service standard—you can find this in the “donut” symbol on the back of the bottle—they are designed to be compatible with each other.

Can You Mix 5W-20 and 0W-20? The Short and Long Answer

So, we get to the core question. You’ve got the context, now you need the verdict. The answer isn’t a simple yes or no; it’s about understanding the situation and the compromise you’re making. This is the heart of any good mix 5w20 and 0w20 guide.

The Short Answer: Yes, for a Top-Off

In an emergency or for a small top-off (a quart or less), it is perfectly acceptable to mix 5W-20 with 0W-20, or vice-versa. The most critical thing for your engine is having the correct amount of oil. Running your engine low on oil is far more dangerous than using a slightly different viscosity for a short time.

Remember this golden rule: Some compatible oil is always better than no oil.

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The Long Answer: Understanding the Compromise

When you mix the two, you aren’t creating a magic new oil. You’re simply creating a blend whose cold-start properties will land somewhere between a 0W and a 5W. The operating temperature protection remains the same (a “20” weight).

If you add a quart of 5W-20 to an engine filled with 0W-20, you’ve slightly thickened its cold-start viscosity. For most drivers in moderate climates, this difference will be negligible. However, if you live where temperatures plummet well below freezing, you are sacrificing some of that crucial cold-flow protection your manufacturer intended.

A Practical Guide: How to Mix 5W-20 and 0W-20 Safely

If you’ve decided a mix is necessary to get you by, follow these steps. Adhering to these mix 5w20 and 0w20 best practices ensures you do it safely and effectively.

  1. Check Your Oil Level Correctly: Park your car on a level surface and wait for the engine to cool down for at least 10-15 minutes. This allows the oil to drain back into the pan for an accurate reading. Pull the dipstick, wipe it clean with a rag, re-insert it fully, then pull it out again to check the level.

  2. Confirm Oil Specifications: Look at the back of both oil bottles. Ensure they both meet the same API service standard (e.g., API SP or SN Plus). This confirms the additive packages are modern and designed to be compatible.

  3. Add Oil Slowly: Use a clean funnel to avoid spills. Add about half a quart of the new oil, then wait a minute or two. Re-check the dipstick. Add more if needed until the level is between the “MIN” and “MAX” lines. Do not overfill!

  4. Plan Your Next Oil Change: Mixing oils is a temporary fix. Make a plan to get a proper oil change with the manufacturer-recommended viscosity at your earliest convenience. This will restore your engine’s specified performance and protection.

Benefits and Common Problems with Mix 5W-20 and 0W-20

While mixing is a useful trick to have up your sleeve, it’s important to weigh the convenience against the potential downsides. Understanding the benefits of mix 5w20 and 0w20 and the risks is key.

The Main Benefit: Emergency Engine Protection

The single biggest benefit is preventing catastrophic engine damage. If your oil light is flickering and you’re a quart low, adding a compatible oil—even if the winter grade is slightly off—is the absolute right call. It keeps metal parts lubricated and saves you from a massive repair bill.

Common Problem #1: Reduced Cold-Start Performance

This is the most significant drawback. If your car is designed for 0W-20, it’s likely a modern engine with very tight tolerances that relies on that ultra-thin oil for immediate lubrication on startup. A 5W-20 mix will be slightly thicker when cold, potentially leading to a tiny bit more wear over time, especially in very cold climates.

Common Problem #2: Potential Warranty Complications

If your vehicle is still under its factory warranty, stick to the book. Using an oil viscosity other than what is specified in your owner’s manual could give a manufacturer grounds to deny a warranty claim for an engine-related failure. For peace of mind, it’s best not to mix.

Common Problem #3: Unpredictable Additive Blend

Every oil brand has a proprietary blend of additives—detergents, anti-wear agents, friction modifiers, etc. While base oils are compatible, mixing two different formulas means the resulting additive package isn’t as precisely balanced as what the engineers designed. It won’t cause sludge, but it might not perform optimally.

A Note on Sustainable and Eco-Friendly Oil Management

Being a responsible DIYer also means thinking about our environmental impact. When it comes to a sustainable mix 5w20 and 0w20 approach, the conversation is about reducing waste and maximizing efficiency.

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Using up a leftover bottle of 5W-20 for a top-off instead of letting it sit on a shelf for years could be seen as a way to reduce waste. However, the most eco-friendly mix 5w20 and 0w20 practice is rooted in long-term engine health.

Using the correct oil specified by your manufacturer ensures your engine runs as efficiently as possible, which can improve fuel economy and reduce emissions. The ultimate goal of any mix 5w20 and 0w20 care guide should be to get back to the recommended oil grade as soon as possible for peak engine performance and longevity.

And remember, always take your used oil and empty plastic bottles to a designated recycling center. Never pour it down the drain or throw it in the trash.

Frequently Asked Questions About Mixing 5W-20 and 0W-20

What happens if I accidentally used 5W-20 for a full oil change in my 0W-20 car?

Don’t panic. Your engine will be fine. You’ve simply switched to an oil that is slightly thicker on cold starts. You might notice a very minor dip in fuel economy or slightly rougher starts in deep winter, but it will not cause immediate damage. Plan to switch back to 0W-20 at your next scheduled oil change.

Can I mix different brands of 5W-20 and 0W-20 oil?

Yes. As long as both oils carry the same API certification (the “donut” symbol), they are designed to be compatible, regardless of brand. Mixing a quart of Mobil 1 5W-20 with Valvoline 0W-20, for example, is perfectly fine for a top-off.

How much 5W-20 can I safely add to 0W-20?

For a top-off, adding one quart is generally considered the safe limit. Any more than that and you are significantly altering the viscosity profile of the oil in your engine. If you find you are more than a quart low, you should investigate the cause of the oil consumption before simply adding more.

Will mixing these oils cause engine sludge?

No. This is a common myth. Modern, API-certified synthetic oils are highly resistant to sludging and are designed to be miscible. Sludge is typically caused by using low-quality oil, severe overheating, or going far too long between oil changes, not by mixing compatible viscosities.

Your Engine, Your Call

The next time you’re faced with a low oil level and a mismatched bottle, you’ll know exactly what to do. You can confidently mix 5w20 and 0w20 for a top-off, understanding it’s a smart, safe, temporary solution to a much bigger problem: running your engine dry.

Your number one priority is always lubrication. By following the best practices in this guide, you can handle the situation like a pro, keeping your engine protected and your mind at ease.

Now you have the knowledge to make an informed decision right there in your garage or on the side of the road. Keep that engine happy, drive safe, and never be afraid to get your hands dirty!

Robert Lozano
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