By Anthony Santiago - Editor-in-Chief

October 19, 2023
can you mix engine oil

You might be wondering if you can mix engine oil.

As an automotive expert and enthusiast, I'm here to shed some light on this common question.

The short answer is YES if the viscosity is the same or close to it. While mixing oil viscosities is not ideal, I have added 5W-40 to a vehicle that takes 5W-30. In addition, I also tried 0w-40 as well as an alternative.

I have encountered the same situation that you might be in right now, where you are low in oil or need more of the same oil for your oil change. 

I highly recommend that you read your owner's manual for recommendations. 

I would NOT use just any oil or trust a gas attendant to fill it with oil. Always check your manual or do a quick Google search.

I have mixed brands of engine oils in the past, and as long as your oil level is between minimum and maximum, you should be okay to run it until your next oil change interval. 

Can you mix synthetic oil with conventional oil?

I would NOT recommend mixing conventional with synthetic oil. Conventional oil doesn't withstand high temperatures as well as full synthetic. You risk gumming up your system if you accidentally keep dino oil for a long time. 

Conventional oil should be changed every 3k-5k miles compared to synthetic oil of 5k-10k miles. An interval of 5k-7.5k is a good range for modern vehicles that use full synthetic. 

We'll look at the potential benefits and drawbacks and offer some tips on when it might be appropriate to mix engine oil. So, let's get started and debunk some myths about engine oil.

Can You Mix Engine Oil?

Yes, you can. You can mix engine oil. 

Your engine might often be burning some oil, and your oil lever light would turn on the dash. In this case, you will need to add 1 quart to your engine. 

It is very common with today's fuel injection and turbo engines that they burn oil. Some manufacturers state that 1 quart per 1,000 miles is normal. The topic of oil consumption has a long history in modern engines. 

Let's review the types of engine oils.

Firstly, Synthetic and conventional oils are the two primary types. Synthetic oil is engineered to perform at the highest levels of protection and performance, while conventional oil, derived from crude, is less refined.

Diesel engine oils are different from gasoline engines since they contain more detergents to help keep the engines burning cleaner. 

What is Oil Viscosity?

Secondly, viscosity is another factor to consider. It measures oil's resistance to flow. Mixing oils with different viscosities will impact the oil's performance in low temperatures, like a cold start. For example, a thicker oil may not flow as well in colder temperatures, causing your engine to work harder. The top number is the protection it offers at higher temperatures. 

The higher the number, the higher the temperature it can withstand. 

Most turbo engines will use either a 0w-40 or 5w-40. However, racing oils can have thicker viscosities like 0W-50. The higher the number of the last number, the thicker the oil.

Are High Mileage Oils Better?

Lastly, the condition of your engine plays a significant role. Older engines may require a different type of oil than newer ones. As an engine ages, the gaskets and seals dry up and harden. 

In this case, using high-mileage engine oil can help soften these gaskets to reduce or stop oil leaks from failing seals.

Brands like Kendall might not be as known to the average driver, but they offer exceptional protection.

These high-mileage oils are not a silver bullet, but they can help reduce weeping as the oil helps rejuvenate the rubber gaskets. 

Oil additives like Liquid Moly Oil Saver can be added to your engine oil to help rehydrate engine seals. I have successfully used this to reduce the rear main seal of our Audi A4. 

Is there a Difference Between Brands of Engine Oil?

Yes, there are differences when using different oil brands. I typically suggest name-brand oils that contain additives to help reduce friction and wear. 

Some of my favorites are Mobil 1 and Pennzoil. 

My simple rule is to use whatever oil is on sale if you are a DIYer. Otherwise, dealerships or specialized auto shops can provide recommendations. 

I would typically skip Supertech from Walmart or Costco since prices are only a few dollars less than more well-known brands. But many Automotive YouTubers swear it's the same.

However, if you have a regular oil change interval, you can definitely use Walmart, Costco, or Off-the-Shelf brands with no issues. 

Regular oil change intervals are more important than the brand you use. 

Important tip: if you're running low on oil and don't have the exact type on hand, mixing oils can be a temporary solution. I have had NO ISSUES topping up with a different brand if I am low on oil. 

Top Reasons You Mix Engine Oil

Cost Saving

One of the primary reasons to mix engine oil is to save on costs. High-quality engine oil can be expensive; some might hesitate due to the cost.

As I mentioned earlier, mixing engine oils can provide a temporary lifeline if you're running low and need to top up immediately.

Using a less expensive oil to supplement the high-quality oil you've already got in your engine can help stretch your dollar further.

This is especially true if you plan to use an engine flush and you need to run the engine for a few thousand miles before the next oil change. 

Remember, though, this is not a long-term solution. It's always better to invest in high-quality engine oil to ensure the longevity and performance of your engine. You can use it as long as the physical properties and the oil grade are correct. 

Quick Convenience

Another reason to mix engine oil is for convenience. Sometimes, you might find yourself in a situation where you don't have the exact type of oil your engine requires. You can mix oils rather than driving with low oil, which can harm your engine.

This is not ideal, but you should always have enough oil in your engine, even though it might be a different grade.

This can be particularly handy in emergencies. For example, if you're on a road trip and your oil light comes on, you might need access to your preferred oil. In this case, mixing oil can temporarily fix until you can get the right oil.

If the oil light turns on, I always carry a spare quart of oil in the trunk.

Considerations when Mixing Oils

While it's possible to mix engine oil, it's essential to remember that there are potential risks associated with this practice. Issues ranging from compatibility to differing oil specifications and manufacturer recommendations may result in unintended consequences for your engine.

Compatibility Issues

Firstly, compatibility issues may arise. Different types of oil have varying chemical compositions.

If incompatible oils are mixed, it could lead to chemical reactions that produce sludge and other harmful deposits.

If you ever mix oils that are very different in makeup or types, I plan to do an oil change in 30 days. This will help reset the oil and provide the proper lubrication for your engine. 

If you have or add more than 1 quart to top up your engine, you might have a bigger issue like an oil leak. 

You will smell burnt oil near the engine if that is the case.

Oil Specifications and Manufacturer Recommendations

It's crucial always to consider your vehicle manufacturer's recommendations. Manufacturers design their engines to operate best with specific types of oil. Ignoring these recommendations and mixing engine oils may reduce engine performance or damage.

Consult your vehicle's manual or a trusted mechanic before mixing engine oil.

Tips for Safely Mixing Engine Oil

Consider Oil Viscosity

Viscosity refers to the oil's resistance to flow. Different viscosities can lead to inconsistent lubrication, eventually harming the engine. When mixing engine oils, make sure they have similar viscosities.

Consult a Trusted Mechanic

Consulting a trusted mechanic is always a good idea if you're in doubt. They can provide professional advice on what oil you can use. 

Final Thoughts

So, we've learned that mixing engine oil doesn't instantly ruin your engine.

However, changing your oil at least once a year is important, if not more. Mixing oil is fine if the viscosity is the same.

However, if you mix viscosities or types in an emergency, changing your oil at your earliest convenience is recommended. Doing so ensures optimal engine performance and extends its lifespan.

Remember, all these steps are for emergencies only. It's always best to follow the manufacturer's guidelines for your vehicle. After all, your engine is the heart of your vehicle. It's worth taking the extra steps to treat it right. 

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Anthony Santiago - Editor-in-Chief

About the author

I am a passionate car enthusiast who likes to help people save money and avoid headaches when it comes to cars. I believe that everyone can find the right car at the right price. I share my tips and experience so you can learn quickly and maximize your next SUV, truck or car purchase.

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