Is It Safe to Mix Engine Oil Brands?

One of the biggest questions many people have when going for an oil change is, "Is it okay to mix different brands of oil?" In short, while it is possible to do this, it is absolutely not recommended. A vehicle's engine is a highly complex machine that operates with extreme precision. Therefore, you must pay much closer attention to the oil you put into it. Let's discuss this deeply from both a technical and practical standpoint.

The Problem with Mixing Chemical Formulas

First, you need to understand that every type of engine oil is made from a combination of two basic components: Base Oil and Additives. The base oil provides the lubrication. Additives are the chemicals added to clean the dirt that settles inside the engine, prevent rusting, and control the oil from thinning out under extreme heat. Now, here is where the problem arises. Different oil companies (for example, Shell, Mobil, Caltex) use completely different chemical formulas to manufacture their oils. The chemicals in one brand can react with the compounds in another brand.

If you have your engine half-filled with one brand of oil and you fill the remaining half with another brand, these chemical substances start to clash. As a result, the quality of the oil breaks down. Sometimes, when these two oils mix, it can create "Sludge"—a thick, mud-like substance. If this sludge gets stuck in the narrow oil passages of the engine, the metal parts of the engine will grind against each other, causing massive damage. Therefore, do not take an unnecessary risk.

Viscosity and Engine Design

The next most important thing is the 'Viscosity' or thickness of the oil. If you are using a 10W-30 oil, do not mix it with another brand's 20W-50 oil. The engine is designed for oil of a specific thickness. When this changes, it becomes difficult for the oil pump to push the oil upwards. Especially when starting the vehicle in the morning, if the oil is delayed in reaching the upper parts of the engine, components like piston rings and the camshaft will wear out rapidly.

Mixing Mineral and Synthetic Oils

Some people ask, "I use Mineral Oil; is it okay to add a little Synthetic Oil to it?" The truth is, the molecular structures of these two are completely different. Synthetic oil is artificially created in a laboratory. Mineral oil is refined from crude oil extracted from the earth. When you mix these two, the superior protection provided by the synthetic oil diminishes, and unwanted deposits can form inside the engine.

In an absolute emergency (for example, if you are on a journey and an oil leak causes the engine oil level to drop significantly), it is not a problem to top it up with whatever oil is available to complete the trip. It is far better to have some kind of oil in the engine than to run it dry. However, remember that as soon as the journey is over in such a situation, you must drain (flush) all the oil and refill it entirely with a single brand.

The Benefits of Sticking to One Brand

There are many advantages to always using the same brand when maintaining a vehicle. By doing so, the metal surfaces inside the engine get accustomed to that specific chemical composition. If you constantly switch brands, the engine's performance can subtly change. The same goes for the oil filter. When you change your oil brand, you must definitely change the filter as well. This is because a small amount of the old brand's oil will remain trapped inside the old filter.

Conclusion

In conclusion, your vehicle's engine is worth hundreds of thousands of rupees. Its lifespan is determined by the oil you put in it. Do not mix whatever oil brands you find just to save a little money or out of laziness. Always use the exact Oil Grade recommended by the manufacturer (found in the User Manual). Buying a 5-liter can of the same brand is always more economical and reliable. If the brand you use is no longer available in the market, drain all the old oil and switch completely to a new brand. That is what a smart vehicle owner should do.