Can You Mix Oil Brands and Weights?

If you’re an experienced driver, by now you should know how important oil is for an engine. Without any oil in the engine, the vehicle is rendered useless because no engine will function long enough without good oil circulating the engine. It allows the components in the vehicle to function and it helps them to stay running for a long time. There are moving components in the engine and they constantly rub against each other when the engine is working. This constant rubbing creates friction, and this creates heat within the oil. To stop this friction, oil is needed to lubricate the engine and absorb the heat that is made by the rubbing parts – this stops the engine from overheating which can harm the longevity of the engine.

Like anti-freeze, oil prevents the engine from heating. Although they don’t work exactly the same, they both help the engine in similar ways. The oil stops the engine from overheating, and it does this by limiting the amount of fraction that’s given out from the components. Rather than the heat being concentrated in one place, it’s transferred throughout the engine. Engine oil also works as a cleaner and it goes around the engine collecting dirt that has built up throughout the engine. Debris can be bad for the engine because it can it can clog up the components and this can cause more friction which will lead to overheating – the engine needs to remain clean in order for it to function properly and a good oil will do this.

Engine oil is made up of several additives and base oils. The base oils lubricate the engine’s moving components to reduce the amount of friction and heat they produce. The additives within the oil helps to keep the oil at the right viscosity so it can maintain its quality under high temperatures. Extreme temperatures within an engine can really be bad for the oil but high quality SAE standard oil will maintain it’s quality in these conditions – this helps to keep the engine lubricated regardless of the temperature its under. Sometimes you can run out of oil and you may only have enough oil left but its from another brand and this can leave you hesitant to pour this new oil into the reservoir.

Can You Mix Oil Brands?

It is safe to mix two different oil brands together and pour them in the oil reservoir. It’s done all the time and it doesn’t cause any harm to the engine. Before an oil change, around 20% of the oil is left in the engine so its fine if to pour a new brand of oil – regardless of the oil viscosity. For example, you can mix a brand like Mobil 1 and another brand AMOSOIL, or conventional oil with synthetic oil. Most oils today are compatible with each other so it’s unlikely you’ll experience problems if you decide to mix the two types of oils together.

Important: If you want to save $100s in servicing, diagnosis, and repair costs, improve your car's performance significantly and increase its value by 1.2x with little effort, download our Beginners Auto Maintenence & Repair Manual now. 

However, just because you have two different types of oils to mix together doesn’t mean you should. Even though conventional and synthetic oils are compatible, mixing brands like AMSOIL with other oil brands or types of oils can reduce the life span and the quality of the oil. Each oil has base oils and this helps to lubricate the engine – they have a specific make up that’s carefully selected by the manufacturer and blended in such a way that the end product will perform well on the engine it’s meant for.

There are also additives in the formula that coordinate each other and work well together. Each company has their own oil formula for each of their different oil brands and another company will have their own formula for each of their brands. If an oil formula is mixed with another oil formula that isn’t compatible with each other, this can degrade the oils performance and it’ll lose its quality – this can be harmful for the longevity of your engine.

For example, AMSOIL has two different oil lines, the OE Series formula and the Signature series formula. The signature series formula has base oils and it’s own carefully selected additive package while the OE Series formula as a completely different base oil and a different additive package. Since the additives have their own characteristics and functions for an engine, this could be offset when the oil is mixed with one that has a different additive package. The additive package is made so precisely that if one oil with different base oils and an additive package is mixed with another oil that has different base oils and additive package, you could end up affecting the balance of the blend.

Topping Off Oil with Different Brands

Since you want to mix oil brands together, you should know that around 15% to 20% of oil is left in the reservoir when you go to do an oil change. This means that each time you’ve went and used a new brand of oil, you’ve actually mixed it with the oil brand of oil that was already there, and chances are the engine didn’t notice the difference. If you are going to top off your oil, ideally you should use the same brand. However, there should be no problems when topping it off with another brand of oil.

Pretty much all oils adhere to an API standard SN which requires solubility between brands, viscosity and formulations. This means that pretty much all oils are compatible with others. As long as your engine is compatible with the two different types of oils, you shouldn’t experience any problems. If you want to check your engine’s compatibility with an oil, then you should check the service manual which can either be under the seat, boot, or the glove box. Vehicles weren’t manufactured for a specific type of oil – that would be ridiculous. Therefore, you shouldn’t hessite to top off your oil with another brand. The most common and compatible types of oils are synthetic and conventional. Other oil types that you can top off the oil with include:

Premium Conventional – this is conventional oil but premium and its one of the most common types of oil that manufacturers recommend – if you look at the service manual, chances are this type of oil is recommended. This type of oil has different grades, and this includes 5W -20, 5W-30, or 10W-30. These are good grades and they’ll maintain a good quality when operating at different temperatures

Full Synthetic – this is higher quality that conventional oil and they’re made for high tech engines that require more performance such as sports cars. They go through specialized test and provide a high viscosity level – this prevents the oil from breaking down at extreme temperatures and prevent oxidation.

Synthetic Blend Oil – synthetic blend oil are mixed with synthetic oil and premium conventional oil – this means they will maintain a high quality when operating at extreme temperature. This type of oil is usually recommended for SUVs and pickup trucks as it provides lubrication for heavy engines.

High Mileage oil – this oil is recommended for vehicles with a high mileage. It protects engines that have been used for a long time and for a lot of miles. It provides longevity to these types of engines.

Mixing Oil Weights

Mixing two different oil weight together is fine and, in most cases, it won’t cause any harm to your engine. It’s advisable not to mix different oils weights together and to always stick to the same viscosity but if you do, try to keep the same brand. For example, mixing different viscosities of Mobil1 shouldn’t cause any issue with your engine.

Mixing two different oil weights won’t cause them to react negatively with each other or to separate because base oils are usually the same. All base oils are made from the same petroleum feedstocks therefore, a lot of oil companies will be using the same base oil. When mixing oil viscosities, it isn’t the base oils in the formulation that’s the problem, it’s the additives between the brands that could cause the problem. Oil additives contain substances like:

  • Viscosity index improvers which will stop the oil from thinning.
  • Fraction modifiers to reduce friction through the engine.
  • Detergents to remove sludge and carbon deposits.
  • Anti-wear to protect the piston rings, cylinder wall, lifters and cams.
  • Dispersants to absorb contaminants that could damage the engine.
  • Anti-oxidants to prevent thickening at high temperatures.
  • Pour point depressants to low the temperature of the wax coagulation alkaline materials to neutralize acids for during the combustion process.
  • Rust and corrosion inhibitors.
  • Pressure additives to prevent metal to metal contact.

These additives vary between different brands and when they’re mixed together, they may not function as planned. The additives in one oil are combined together at a specific amount to have a desired outcome and if mixed with a different brand with a different additive makeup, it can ruin the quality of the oil all together. Different weights of the same brand have different amount of viscosity index improvers that stop the oil from thinning and this isn’t what causes the problem, it’s the other additives in the oil of other brands that can cause the problem.

If you’re wondering if you’ll be able to mix different viscosity grades such as 5w-30 low viscosity oil and 5w-40 which will have a higher viscosity, then it’s expected that the combined oil will have properties of a thicker oil than the 5w-30 oil – doing this will rebalance the viscosity characteristics but the resulting product should still work as oil should.

If You Don’t Check Your Oil, the Engine will Fail

If you want to ensure that your engine has longevity, you’ll need to make sure that you’re putting the right oil and doing the right checks on the engine. There’s a lot to know about oil such as the quality, additives, consistency, brand, and temperature that can all affect the way the engine runs. Failure to maintain the engine by putting in the wrong oil can cause the engine to deteriorate quickly. The key to a long-lasting engine is maintenance. Oil is just one form of engine maintenance and even this needs to be done right. Failure to main your vehicle as a whole can lead to all sorts of problems.

If you want to avoid engine problems or any other problems and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.

A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.

Bottom Line

When using properly formulated oil, you shouldn’t feel the need to add additives because it can work negatively with the additives that were already naturally added to the oil. You should also stay away from aftermarket oils because they can offset the characteristics of the additives that were put into the original oil. If you have no other option, then it isn’t the end of the world if you’ve added two different brands of oil. Since oil is already remaining in the reservoir when you decide to change oils, oils brands are mixed much more often than you think, and nothing usually happens in this case.

In conclusion, mixing two different oil weights isn’t recommended, but if you do go ahead mix them, you shouldn’t notice any problems. If you are going to mix different SAE grades, then you should stick to the same brand. If the brand and the SAE grades are different, try sticking with the same type of oil. For example, if it’s conventional oil and you want to mix it with another conventional oil that’s a different brand and a different grade, then it should be fine.

If you can, stick with the same oil that you normally use when doing an oil change – this includes the brand and the formulation. It’s very unlikely that the engine will be damage when the oil is mixed – usually, it can’t even tell the difference when two different types of oils are in the engine and it’ll continue to run fine. However, in the long term, this could damage the longevity of the engine. If you are going to mix oils, try to stick to the same brand, or the same SAE standard.