What Happens If You Mix 0W20 And 5W20 – A Diyer’S Guide To Safe
In an emergency, mixing 0W-20 and 5W-20 oil is acceptable to top off your engine and is far better than running on low oil. The resulting mixture will have a cold viscosity somewhere between the two, slightly reducing cold-start performance but causing no immediate harm. However, you should not do this for a full oil change and should return to your manufacturer’s recommended viscosity at your next service.
You’re standing in your garage or the auto parts aisle, staring at two bottles of synthetic oil. Your car, which specifies 0W-20, is a quart low, but all you have on the shelf is a bottle of 5W-20 left over from a previous vehicle. The question hits every DIYer eventually: what happens if you mix 0W-20 and 5W-20?
It’s a common dilemma that can leave you second-guessing a simple top-off. We get it. You want to protect your engine, but you also need a practical solution right now. At EngineNeeds, we believe in empowering you with clear, expert knowledge to make confident decisions.
This complete guide will cut through the noise and give you the straight answer. We’ll break down exactly what happens inside your engine, explain when it’s safe and when it’s not, and provide best practices so you can handle the situation like a pro and keep your rig running strong.
Decoding the Numbers: What Do 0W-20 and 5W-20 Really Mean?
Before we dive into mixing, let’s quickly demystify those numbers on the bottle. Understanding them is the key to understanding the impact of mixing. This isn’t just trivia; it’s the foundation of your engine’s health.
The “W” for Winter: Cold-Start Viscosity Explained
The first number followed by a “W” (which stands for Winter) rates the oil’s viscosity, or its thickness and ability to flow, at cold temperatures. A lower number means the oil is thinner and flows more easily when your engine is cold.
- 0W: This oil is tested at -35°C (-31°F) and flows very well in extremely cold conditions, providing faster lubrication to critical engine parts during a frigid start-up.
- 5W: This oil is tested at -30°C (-22°F). It’s still excellent for most cold climates but is slightly thicker than 0W oil at the same low temperature.
Think of it like honey versus water. On a cold morning, the 0W oil is more like water, getting where it needs to go instantly. The 5W is a bit more like cold honey—still pourable, but a little slower to start.
The “20” for Operating Temp: Why This Number Matters Most
The second number—in this case, “20”—indicates the oil’s viscosity at the engine’s normal operating temperature (around 100°C or 212°F). Since both oils are “20-weight” at temperature, they are designed to provide the exact same level of protection once your engine is warmed up.
This is the most critical point: when your engine is running at normal temp, 0W-20 and 5W-20 behave identically. The only difference between them is their performance during a cold start.
What Happens If You Mix 0W-20 and 5W-20 in Your Engine?
So, you’ve poured a quart of 5W-20 into an engine that’s mostly full of 0W-20. What’s actually going on in the oil pan? This section of our what happens if you mix 0w20 and 5w20 guide breaks it down.
The Immediate Result: Creating an “In-Between” Oil
When you mix the two, they blend completely. You don’t get layers of different oils. Instead, you create a new blend with a viscosity that’s an average of the two, weighted by the amount of each you used.
If your engine holds five quarts and you add one quart of 5W-20 to four quarts of 0W-20, you’ll end up with an oil that has a cold viscosity somewhere between 0W and 5W. It might effectively be a “4W-20” or “3W-20,” if such a grade existed.
The operating viscosity remains a “20,” which is excellent news for your engine’s protection while driving.
Short-Term Effects: Is It Safe for a Top-Off?
For a short-term top-off (e.g., adding one quart to a five-quart system), mixing these two oils is generally safe and will not cause damage. The primary goal in a low-oil situation is to get the level back up to the full mark.
Running your engine on low oil is far more dangerous than running it on a slightly mixed viscosity. Low oil can lead to oil starvation, overheating, and catastrophic engine failure.
The only noticeable difference you might experience is slightly slower cranking on a very cold morning. For most drivers in moderate climates, this change will be imperceptible.
Long-Term Consequences: Why It’s Not a Good Habit
While a one-time mix is fine, you shouldn’t make a habit of it. Consistently using 5W-20 in an engine designed for 0W-20 (or mixing for every oil change) can lead to a few issues over the long haul.
- Reduced Fuel Economy: Modern engines specifying 0W-20 are built with very tight tolerances. The thinner 0W oil reduces internal friction on startup, which contributes to the vehicle’s designed fuel efficiency. A slightly thicker cold oil can marginally decrease your MPG.
- Increased Cold-Start Wear: The most wear and tear on an engine happens in the first few seconds after starting, before oil has fully circulated. Using a slightly thicker oil can fractionally delay that lubrication, leading to microscopic wear that can add up over tens of thousands of miles.
The Verdict: When It’s Acceptable to Mix and When to Avoid It
Knowing the theory is great, but you need practical advice. Here are some real-world scenarios to help you make the right call.
Emergency Situations: Low Oil Is Worse Than Mixed Oil
This is the golden rule. If your dipstick shows the oil level is at or below the “add” line and the only oil you can find is 5W-20 (for your 0W-20 engine), use it without hesitation. The benefit of getting the oil level back to a safe range far outweighs the minor, temporary change in cold viscosity.
This is one of the most important what happens if you mix 0w20 and 5w20 tips we can offer: protect your engine from oil starvation first and foremost.
Routine Oil Changes: Stick to the Manufacturer’s Recommendation
When performing a full oil change, always use the viscosity grade specified in your owner’s manual. There is no benefit to mixing oils for a fresh fill. Your engine was designed and tested with a specific oil in mind to provide optimal performance, protection, and fuel economy.
Using the correct oil is also critical for maintaining your vehicle’s warranty. If an engine issue arises and the manufacturer discovers the wrong oil was used, they could deny your claim.
A Note for Off-Roaders and Performance Drivers
For those of us pushing our vehicles hard, oil is not just a lubricant; it’s a critical performance component. While the 0W-20 vs. 5W-20 debate is mostly about cold starts, always stick to the manufacturer’s spec unless you’ve made significant engine modifications that a professional tuner has advised require a different oil weight.
Extreme conditions don’t change the fundamental need for the right viscosity at operating temperature.
A Practical Guide: How to Handle a Mixed Oil Situation
Let’s walk through the steps. Here’s how to what happens if you mix 0w20 and 5w20 in the real world.
- Assess Your Situation: Is your oil light on? Is the dipstick dangerously low? If so, it’s an emergency. If you’re just planning a routine oil change, it’s not.
- Top Off Safely (If Needed): If you’re in an emergency, add just enough of the “wrong” viscosity oil to bring the level back into the safe zone on the dipstick (between the “add” and “full” marks). Don’t overfill it.
- Make a Note: Keep a record of what you added and when. This is good practice for any DIY mechanic.
- Plan Your Next Oil Change: Don’t stress, but don’t forget. Plan to perform a full oil change with the correct viscosity oil at your next scheduled interval, or even a little sooner if it gives you peace of mind. The small amount of mixed oil will be drained out, and your engine will be back to 100% spec.
Common Problems and Myths About Mixing Oil Viscosities
Let’s clear the air on a few things. There’s a lot of old “garage wisdom” out there that isn’t always accurate.
Myth: Mixing Oils Will Instantly Damage Your Engine
This is the biggest fear, but it’s simply not true for similar, modern synthetic oils like 0W-20 and 5W-20. They are formulated to be compatible. Mixing them won’t cause the oil to gel, sludge, or break down. The only change is a slight alteration of the cold viscosity.
Common Problems with What Happens If You Mix 0W-20 and 5W-20
The real-world “problems” are subtle and long-term, not catastrophic. They include a slight, often unnoticeable, decrease in fuel economy and a marginal increase in wear during cold starts, especially in very cold climates. For a one-time top-off, these issues are negligible.
Sustainable and Eco-Friendly Oil Practices for the DIYer
Being a responsible car owner goes beyond just maintenance. Following some eco-friendly what happens if you mix 0w20 and 5w20 best practices ensures we protect our environment as well as our engines.
Choosing the Right Oil to Reduce Waste
One of the most sustainable what happens if you mix 0w20 and 5w20 actions you can take is using the correct oil from the start. This maximizes your engine’s efficiency, leading to better fuel economy and fewer emissions. It also prevents the waste of having leftover, mismatched oil bottles on your shelf.
The Importance of Proper Oil Disposal
Whether you’re doing a full oil change or just tidying up, never pour used oil down the drain or on the ground. A single quart of oil can contaminate thousands of gallons of water. Always collect your used oil in a sealed container (like an empty oil jug) and take it to an auto parts store or a local recycling center. Most stores will take it for free.
Frequently Asked Questions About Mixing 0W-20 and 5W-20
Can I mix different brands of 0W-20 and 5W-20?
Yes. As long as both oils meet the same API (American Petroleum Institute) service standard (e.g., API SP) listed in your owner’s manual, it is safe to mix different brands for a top-off. The compatibility of the additives is a much bigger concern with older, conventional oils than with modern synthetics.
What if my car requires 5W-20 and I add 0W-20?
The same logic applies in reverse. Adding a quart of 0W-20 to a 5W-20 engine is also safe in a pinch. You will be slightly improving your engine’s cold-start performance with no negative effects on its protection at operating temperature. Again, revert to the recommended 5W-20 at your next full oil change.
Will mixing these oils void my vehicle’s warranty?
A one-time emergency top-off is highly unlikely to cause an issue or be detectable. However, if you consistently use the wrong viscosity oil and an engine failure occurs, a manufacturer could potentially deny a warranty claim. This is why following the what happens if you mix 0w20 and 5w20 care guide and sticking to the recommended oil for full changes is the safest bet for your warranty.
The final word is one of practicality and perspective. While the engineers who designed your engine chose 0W-20 for a reason, they also know that an engine with slightly mixed oil is infinitely better than an engine with no oil.
Don’t panic if you have to mix them to get home safely or to get through the week. Just be a smart DIYer: understand what’s happening, correct it at the next opportunity, and always prioritize the oil level above all else. Keep that engine lubricated, and it will keep you on the road and the trail for years to come.
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