Can motor oils of the same brand but different grades be mixed?

[DelLaura]

Unless you have a very deep understanding of the composition and content of motor oil, it is best not to mix different oils. If the oil is consumed, you should have a spare oil of the same type as the one in the car. After adding a different oil, please change the oil and perform maintenance as soon as possible. During maintenance, if you are changing the brand of the oil, try to drain the oil from the engine as thoroughly as possible. The cleaner the better. Use gravity to drain the oil, and it is best to leave it for more than 2 hours. Some functions of engine oil are as follows: 1. Cleaning function: The cleaning function refers to removing residues such as carbon and oil produced by combustion, or dissolving these residues in the oil. Through the oil circulation, the impurities are carried to the engine oil filter. Engine oil can clean the engine and remove impurities from it, protecting metal surfaces from corrosion caused by acids formed during combustion. 2. Cooling function: The cooling function refers to cooling the engine. Engine oil can assist the cooling system (such as water, radiator, water pump, cooling circulation system, and airflow passing through the engine and oil pan) in removing the heat generated by the pistons. When cooling the pistons, gasoline should be sprayed from the opposite side. Therefore, the oil must have excellent cooling performance and be able to withstand high temperatures.

[McBrianna]

You know, I've driven quite a few cars, and mixing different viscosity grades of engine oil from the same brand is really not a good idea. I remember one time when I was out and the oil light came on, and I only had a bottle of 5W-30 in the car, but I normally use 10W-40. To save trouble, I mixed in half a bottle. After two days of driving, the engine started making slight abnormal noises, and I felt like there was insufficient lubrication. Upon checking, the oil pressure was unstable. Experts say that different viscosity grades indicate different oil thicknesses, and mixing them can result in uneven oil film thickness, failing to properly protect internal components and potentially causing wear or temperature control issues. Long-term use will definitely harm the engine. Even if the same brand has similar additives, the formulation is designed for specific viscosity grades. For safety, I always stick to one viscosity grade, regularly check the oil level, and replace it when it's low. It's not just about saving money—protecting your car's lifespan is the most cost-effective approach. I recommend you develop this habit too.

[StMadeline]

As a detail-oriented car owner who has studied motor oil, I can confirm that mixing different viscosity grades from the same brand is problematic. Oil grades like 5W-30 indicate low-temperature fluidity and high-temperature viscosity. When you mix 5W-30 with 10W-40—one thinner and one thicker—the blended oil's overall performance becomes compromised, significantly reducing lubrication effectiveness. This may lead to increased internal engine friction or insufficient cooling. While using the same brand minimizes additive conflicts, viscosity disparity remains a major issue. Small emergency mixtures are acceptable, like adding half a bottle of a different grade for short trips when running low. However, based on my experience, an immediate oil change is necessary afterward, as cloudy oil indicates increased contaminants. To properly protect your vehicle, always consult the manual for the specified grade—don't risk long-term damage for minor savings. Safe driving is paramount.

[LaSimon]

Absolutely not recommended to mix different viscosity grades of the same brand's engine oil. Different viscosities can lead to uneven oil distribution, affecting lubrication effectiveness, and may cause engine noise or accelerated wear in the short term. Adding a small amount in an emergency might be barely acceptable, but it carries high risks. Safety first—it's best to stick with a fixed viscosity grade.

[Luca]

I've had a similar experience. During a road trip, I ran low on engine oil and had to mix in some 5W-40 I found nearby with my usual 0W-30. I drove a few hundred kilometers without major issues, but I've consulted experts - mixing oils from the same brand is better than mixing different brands, at least there's less additive conflict. However, using oils with significantly different viscosities (too thick or too thin) may cause unstable engine operation, and it's absolutely not recommended long-term. Next time, I'll carry a spare bottle of the standard oil to avoid last-minute panic. Simply put, mixing oils isn't a permanent solution - regular maintenance is the real way to save both hassle and money.

[ElleRose]

From my experience, engine oil not only lubricates but also handles cooling and cleaning. Mixing different grades disrupts the original formula balance. For example, blending 5W-30 with 10W-40 creates a significant viscosity difference, leading to poorer oil flow. This may cause sludge or carbon deposits inside the engine, eventually affecting power output and fuel efficiency over time. While additives from the same brand may be similar, compatibility isn't guaranteed—I've even seen cases where mixed oil caused faster dipstick discoloration. Small mixes for emergencies are acceptable, but prompt oil replacement is crucial to prevent premature engine aging. The best practice is choosing the correct grade and maintaining regular oil changes.