What Causes Increased Fuel Consumption After an Oil Change?

[ColeLynn]

The reasons for increased fuel consumption after an oil change: The viscosity of the new oil is higher than before. For example, if the original oil viscosity was 5w-30 and the new oil viscosity is 5w-40, the increased viscosity leads to greater resistance, resulting in higher fuel consumption. Definition of fuel consumption: Fuel consumption per 100 kilometers refers to the amount of fuel a vehicle consumes when driving a certain speed over 100 kilometers on the road. It is a theoretical indicator for vehicles. Calculation of actual fuel consumption: Fuel consumption per 100 kilometers = Volume of fuel consumed (liters) ÷ Distance traveled with that fuel (kilometers) × 100. For example, if a car consumes 4 liters of fuel to travel 50 kilometers, then the fuel consumption per 100 kilometers = 4 liters ÷ 50 kilometers × 100 = 8 liters/100 kilometers. The fuel consumption per 100 kilometers is not fixed; factors such as road conditions, load, temperature, and whether the air conditioning is on can all affect fuel consumption.

[DeJayce]

Over the years as a mechanic, I've seen many people report increased fuel consumption after an oil change, which usually stems from several common causes. For instance, using oil with incorrect viscosity specifications—if the engine is designed for 5W-30 but switched to a thicker oil like 10W-40, the increased internal friction resistance naturally leads to higher running fuel consumption. Another issue is overfilling the oil beyond the maximum mark on the dipstick, causing abnormal engine pressure and extra workload during operation, as if dragging an additional burden. Additionally, the oil change process might accidentally disturb the air filter or intake system, clogging the air passage and reducing combustion efficiency. I recommend first checking the oil level with the dipstick and draining any excess; ensuring the oil used matches the vehicle manual specifications; then driving for a few days to observe. If consumption remains high, inspect tire pressure or fuel lines for leaks—addressing these issues promptly can prevent engine damage.

[LenaAnn]

I've been driving for over 20 years and often experience increased fuel consumption after oil changes, mostly due to my own improper operations. For example, last time I went to a roadside shop for an oil change, they filled it with high-viscosity, low-quality oil and overfilled it. As a result, after a few days of driving, the engine was humming, and fuel consumption increased by 8%, which was really not worth it. Later, when I changed the oil myself, I paid special attention to the oil level and specifications, only adding the recommended oil and slowly pouring it to the middle of the dipstick mark—everything returned to normal immediately. Another issue is that during oil changes, I might have overlooked overall inspections, such as aging air filters or coincidental spark plug problems. I believe an oil change shouldn’t significantly affect fuel consumption. If it really increases, don’t panic. First, use a mobile app to record data for a few days and compare the changes. Then check small details like the oil dipstick and tire pressure—most of these can be handled through DIY, saving on repair costs. Developing a habit of regular car checks is key.

[SanHarmony]

Increased fuel consumption after an oil change is mostly caused by oil-related issues. Using oil with mismatched viscosity increases engine resistance; for example, replacing 30-weight oil with 40-weight oil thickens the oil film, hindering power output. Overfilling the oil beyond the maximum line also increases engine load and reduces fuel efficiency. Check if the oil level is correct and ensure the specifications match. Additionally, oil quality or contaminants affecting combustion, or coincidental factors like decreased tire pressure, could be at play. It's recommended to use oil as specified in the manual and monitor fuel consumption trends after the change.