Rick's Free Auto Repair Advice

Mix motor oil brands?

Is there any danger if you mix oil brands?

Let’s say you’re dipstick shows you’re down a quart of oil since your last oil change. You don’t have the exact same brand as was used by the shop. The oil you have is the same viscosity and has the same oil rating (SN, SN+, etc), but it’s a different brand. So is it ok to mix oil brands? Yes.

Every brand is a different recipe

Some motor oil manufacturers refine their oil from crude all the way to Group III or Group IV base stock, while other motor oil brands are really just made by blenders. A blender is a company that buys the base stock on the open market and mixes in additives to make the oil meet a certain API grade.

What products are added to base stock to make it suitable for your engine?

All motor oil refiners and blenders add additives to the base stock to control chemical breakdown,  maintain viscosity, enhance lubricity, and control contamination.

To controlling chemical breakdown, refiners and blenders add:

• Detergent additives to clean and neutralize oil impurities and prevent deposits inside the engine.
• Corrosion or rust inhibitors to slow rust formation on ferrous metal components.
• Anti-oxidation additives to slow oxidation.
• Metal deactivators prevent oil oxidation by creating a thin protective film on metal surfaces.
• Acid neutralizers to combat acid formation in the crankcase

To control the oil’s viscosity, they add:

• Viscosity improvers (VI) combat oil’s natural tendency to thin as it heats up. Most VI additives are coiled polymer molecules that uncoil as they heat. The uncoiled molecules take up more space to maintain the oil’s viscosity. VI is mostly used in conventional multi-viscosity oils and more of it is used in oils with a wider viscosity range like 10W-50, as opposed to short ranges like 0W-20. However, true synthetic oil (Group IV) oil are engineered to meet multi-grade specifications without VI.
• Pour point depressants are used mostly in conventional oils to improve the oil’s ability to flow at lower temperatures.

To improve lubricity, refiners and blenders add:

• Friction modifiers. In the past, refiners and blenders used zinc. However, zinc can degrade the catalytic converter, so manufacturers have switched to more expensive molybdenum disulfide. The “Moly” lubes are actually better at increasing lubricity than the older zinc additives and can improve mileage by reducing friction.
• Extreme pressure additives are used to bond to metal surfaces, keeping metal components apart even at high pressure.
• Anti-wear additives precipitate out of liquid suspension under high heat conditions to melt and form a protective film on metal parts.

To control oil contamination, refiners and blenders use:

• Dispersants to keep particulate matter suspended in the liquid, so it can be captured by the oil filter. Dispersants also prevent contaminants from coagulating.
• Anti-foam and de-foaming agents act to prevent foam formation or reduction of foam caused by rotating components sloshing into the oil in the sump. Air in motor oil can cause serious problems. Oil doesn’t compress. However, if the oil picks up air, it can’t be pumped as efficiently. Since air acts as an insulation, air in oil also decreases its ability to transfer heat away from high friction areas. Air in motor oil also increases oxidation, resulting in pitting and corrosion.
• Anti-misting agents prevent the oil from atomizing under high pressure.

Refiners and blenders buy their additives on the open market

Few if any refiners or blenders manufacture their own additives. They buy them from well known vendors. However, since the price and availability of these additives fluctuate under market conditions, the exact type, brand, and amount of each additive can vary, not only from one manufacturer to another, but also from one period of time to another. In other words, one refiner’s additive package (or “additive recipe”) can change from one batch to another, while other refiners or blenders may use an entirely different additive package.

The variability in additive packages is why some purists say that you should never mix motor oil brands because one brand’s package may react with the oil that’s already in your crankcase. There’s a small kernel of truth to that. But it’s a really minor point. In the real world, adding a quart of a different brand is far better for your engine than continuing to drive while it’s low by a quart. Obviously, the best case scenario is to add the same brand. But you won’t harm your engine if you add a different brand of the same type, viscosity and API rating.

The only caveat—

Some of the new GF-6 oils coming onto the market are backwards compatible and some are not

GF-6A oil is backwards compatible with older engines. It has better durability to mitigate low speed pre-ignition (LSPI). It has better fuel economy than the current SN+ oil.  It’s available in 0W-20, 5W-20, 0W-30, 5W-30 and 10W-30 viscosity grades

GF-6B  oil is NOT backwards compatible with older engines. It also has better durability to mitigate low speed pre-ignition (LSPI). It has better fuel economy than the current SN+ oil. It is only available in 0W-16 viscosity grade.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN