Does Mixing Engine Oils Affect the Engine?
3 Answers
Yes, it can have an impact. Different types of oils contain different chemical substances, and mixing them may lead to accidents, posing significant safety hazards. It is advisable to avoid mixing oils whenever possible, as it becomes difficult to accurately assess the quality of the oil blend. If mixing is necessary under special circumstances, certain mixing principles can be followed. Some of the functions of engine oil are as follows: 1. Cleaning Effect: The cleaning effect refers to removing residues such as carbon and oil produced during combustion, or dissolving these residues in the oil. Through the oil circulation, impurities are carried to the engine oil filter. Engine oil cleans the engine and removes impurities, protecting metal surfaces from acid corrosion formed during combustion. 2. Cooling Effect: The cooling effect refers to cooling the engine. Engine oil assists the cooling system (such as water, radiator, water pump, cooling circulation system, and airflow passing through the engine and oil pan) in dissipating the heat generated by the pistons. When cooling the pistons, gasoline is sprayed from the opposite side. Therefore, engine oil must have excellent cooling properties and be able to withstand high temperatures.
Mixing engine oils does have negative effects. From my years of repair experience, chemical reactions between additives from different brands can cause conflicts. For example, detergents and antioxidants may interact to form deposits that clog oil passages, and it may also alter the overall viscosity, affecting lubrication and sealing performance. Long-term mixing can lead to accumulated sludge, making the engine internals resemble rust, accelerating bearing wear and increasing oil consumption. I've seen many customers who casually mix oils experience noise issues within just 20,000 to 30,000 kilometers, so I always remind them to choose oils of the same brand and grade. In emergencies where oil is low, you can mix a small amount of oil with the same viscosity, but you should replace it entirely with fresh oil as soon as possible to clean out the residues. Regularly check the oil dipstick; if it turns black, it's time for a change.
With decades of driving experience, I really don't recommend mixing engine oils. Once when I ran low on oil on the highway, I added a different brand as an emergency measure. The engine noise increased slightly, but I managed to drive a few hundred kilometers. Later, the mechanic said mixing oils could cause uneven viscosity, affecting piston ring sealing and leading to increased fuel consumption. Incompatible additives can also make the oil film unstable, potentially wearing down cylinder walls over time. I suggest keeping the manual handy to check the specified viscosity. Mixing once in a while is fine, but don't make it a habit. When changing oil, drain it all completely for smoother engine operation. Choosing a reliable brand and sticking to it throughout saves both hassle and money.
