Can You Safely Mix 10w30 and 5w30 Motor Oils?

Have you ever been in a situation where your car needs an oil change, but you don’t have enough of the right oil on hand? You may be tempted to mix whatever motor oils you have available, like 10w30 and 5w30. But is this safe for your engine?

Can you mix 10w30 and 5w30 motor oils? The short answer is yes, you can mix 10w30 and 5w30 under certain circumstances. However, it’s generally not recommended to mix motor oils with different viscosities on a regular basis.

In this detailed guide, we’ll cover everything you need to know about mixing 10w30 and 5w30, including:

• What 10w30 and 5w30 motor oil grades mean
• Potential risks and issues with mixing 10w30 and 5w30
• When it may be okay to mix 10w30 and 5w30
• Best practices for mixing motor oils
• Signs of engine problems from mixed oils
• How to properly transition between motor oil grades
• Answers to frequently asked questions about mixing oils

Equipped with this information, you’ll be able to make an informed decision about whether mixing 10w30 and 5w30 is suitable for your vehicle’s engine. Let’s get started!

What Do 10w30 and 5w30 Mean? Understanding Motor Oil Grades

To understand whether it’s okay to mix 10w30 and 5w30, you first need to know what these oil grades signify.

10w30 and 5w30 refer to the viscosity grades of motor oil. Viscosity is a measure of an oil’s resistance to flow. Higher viscosity oils are thicker, while lower viscosity oils are thinner.

The number before the “w” stands for the oil’s viscosity at low temperatures or during cold starts. The number after the “w” indicates viscosity at high engine operating temperatures.

For example:

• 10w30 flows like a 10-weight oil when cold, but thickens to a 30-weight oil when hot.
• 5w30 acts like a 5-weight oil in cold temperatures, and reaches 30-weight viscosity when the engine warms up.

So 5w30 is a lighter viscosity oil overall compared to 10w30. The lower cold rating of 5w30 makes it flow faster when the engine is first started.

Key benefits of 5w30:

• Improved oil flow and lubrication in cold weather starts
• Can help increase fuel efficiency and mileage
• Meets requirements for many modern engines

Advantages of 10w30:

• Better protection at high temperatures
• Handles wear well in older engines
• Slightly thicker oil film at operating temp

Now that you understand what these viscosity grades mean, let’s look at whether it’s a good idea to mix them.

Is It Okay to Mix 10w30 and 5w30 Motor Oils?

Whether mixing 10w30 and 5w30 causes issues depends on a few key factors:

• Oil chemistry – Mixing oils with vastly different chemistry/additives is risky.
• Viscosity differences – Blending oils with very different viscosities can alter lubrication.
• Climate and engine – Some conditions are more suitable for mixed oils.

Mixing 10w30 and 5w30 can be done safely in certain situations. But generally, it’s best not to make a habit of blending different viscosity motor oils.

Potential Issues with Mixing 10w30 and 5w30

There are a few potential downsides to mixing 10w30 and 5w30 oils:

• The resulting oil viscosity may be too thin or too thick for your engine. This can affect lubrication and oil pressure.
• Additives that help with cleaning, friction and wear may become unbalanced. This can impact engine protection.
• Contaminants in one oil can transfer to the other, reducing oil quality.
• Incompatible oil chemistry can lead to oil thickening or breakdown. This reduces lubrication life.
• Over time, engine sludge and deposits may build up from mixed oils.

If you drive in extreme hot or cold, mixing these viscosities is not recommended. The mixed oil viscosity may end up being unsuitable for the climate.

For these reasons, auto manufacturers advise against blending different viscosity oils on a regular basis. Doing so requires careful attention to oil condition and engine performance.

When May It Be Okay to Mix 10w30 and 5w30?

There are a few cases where mixing 10w30 and 5w30 might be acceptable:

• You need to briefly top off the oil between changes with a different grade. Monitor oil levels closely.
• Ambient temperatures are moderate, around 10-35°C. The mixed viscosity will be within acceptable range.
• The oils meet all the same specifications and are from the same brand. Chemistry and additives will be compatible.
• Your engine does not have strict viscosity requirements. Light trucks or older engines can handle variance.
• The oil ratio is heavily skewed, like 80% 10w30 and 20% 5w30. This minimizes viscosity impacts.

However, it’s still best practice to avoid mixing viscosities whenever possible. Use the same grade recommended by your manufacturer at each oil change.

Next, let’s go over some tips for mixing 10w30 and 5w30 more safely if needed.

Best Practices for Mixing 10w30 and 5w30 Motor Oils

While mixing 10w30 and 5w30 isn’t generally recommended, circumstances may force you to combine them occasionally. Here are some guidelines to follow:

• Check oil chemistry. Only mix oils of the same base stock (conventional, synthetic blend, full synthetic). Match certifications like GF-5, SN, SM.
• Add a small amount of the secondary oil, no more than 1 quart to 4-5 quarts of the primary viscosity. This limits viscosity impacts.
• Use the lower viscosity as the primary oil in cold climates. For example, mainly 5w30 with some 10w30 in winter. The opposite for very hot regions.
• Check the dipstick. Ensure the mixed viscosity isn’t too thin or thick when warm. Outside the recommended range can indicate issues.
• Watch for changes in oil pressure. Lower pressure with a thin mix may signal insufficient lubrication. High pressure points to thickening.
• Avoid prolonged use of mixed oils. Plan to return to a single viscosity grade at your next oil change.
• Consider an additive for higher mileage engines to help manage contaminants. But don’t over-treat.

Following these precautions will help mitigate risks when forced to mix 10w30 and 5w30. But it’s still wise to avoid mixing different viscosity oils whenever you can.

Signs of Engine Problems Caused by Mixed Oils

How can you tell if blending 10w30 and 5w30 oils has caused issues in your engine? Here are some symptoms to watch for:

• Increased oil consumption. May indicate oil is too thin, failing to adequately coat components.
• Oil leaks. Thinner mixed oil could seep from seals and gaskets.
• Knocking, clattering or ticking noises from the engine. Could signal insufficient lubrication.
• Significant changes in oil pressure readings. May point to unsuitable oil viscosity.
• Black, sludgy oil on the dipstick. Can mean additives are unbalanced.
• Rattling from the timing chain area. Thinner oil may fail to dampen chain movement.
• Overheating problems. Lower viscosity mixed oil doesn’t cool as well.
• Higher than normal emissions. Reduced lubrication can increase exhaust pollutants.

Don’t ignore new engine noises, leaks or other odd symptoms. Have your mechanic inspect for issues if you notice anything out of the ordinary.

How to Properly Transition Between Motor Oil Grades?

Rather than mixing viscosities halfway between changes, it’s much better to switch completely when required. Here’s the proper process:

• Fully drain old oil from the engine, replacing the filter as well. No remnants should be left.
• Use an oil flush additive like Liqui Moly Engine Flush when making a big viscosity jump. This cleans deposits.
• Refill with the new viscosity grade, following fill instructions. Double check the dipstick.
• Drive conservatively for the first couple hundred miles to help the new oil fully circulate.
• Follow manufacturer specifications for recommended oil grades at different temperatures. Don’t deviate without good reason.
• Adjust future oil change intervals based on oil type and driving conditions. Heavier use needs more frequent changes.

With this protocol, your engine will operate safely on the correct viscosity oil for each season or climate. Don’t cut corners to save a few bucks on oil changes.

Frequently Asked Questions About Mixing Motor Oils:

You probably still have a few more questions about mixing 10w30 and 5w30. Let’s address some common oil blending FAQs:

Is it okay to mix 10w30 and 5w30 in an older engine?

Mixing viscosities is riskier in higher mileage, worn engines. The clearances are looser and more sensitive to changes in oil thickness. Stick to the manufacturer grade.

Can I mix synthetic and conventional 10w30?

Avoid mixing synthetic and conventional oils. The chemistry differs greatly. Stick with all conventional or all synthetic/blend each change.

What if I’m low on oil and need to drive 100 miles?

Top off with 1 quart of the other grade only to reach the minimum mark. Get an oil change ASAP after. Monitor the engine closely.

Should I mix in an additive if I have to combine viscosities?

Additives aren’t required but can help. Choose a reputable brand and follow treat rate directions. Don’t over-treat the oil.

Is it ever okay to mix 10w30 and 5w30 50/50?

A 50/50 mix of different viscosities is never recommended. The overall viscosity will be too far from either grade. Stick to 80/20 ratios at most.

Conclusion: Should You Mix 10w30 and 5w30?

While it is technically possible to mix 10w30 and 5w30 motor oils, doing so on a regular basis is not generally recommended. The differences in viscosity can lead to inadequate lubrication and other engine issues over time.

Here are some final tips on combining 10w30 and 5w30:

• Check that oil chemistry is compatible before mixing
• Use caution and limit blending to a minimum
• Thoroughly transition between grades at oil changes
• Closely monitor engine noise, leaks, and oil pressure
• Avoid prolonged use of mixed viscosity oils

In most cases, it’s best to use only the motor oil grade specified by your manufacturer. The exceptions are limited situations where blending minimally to top-off oil level is unavoidable.

With the information in this guide, you can make wise decisions about mixing 10w30 and 5w30. Follow the engine manufacturer’s oil requirements whenever possible for optimal performance and protection.