Why does fuel consumption increase after changing engine oil?
2 Answers
New engine oil has a higher viscosity than used oil, which creates resistance during engine operation. Although the resistance is not significant, it can slightly increase fuel consumption. Here are the relevant explanations: 1. Purpose of changing engine oil: Adding new oil serves to lubricate and protect internal engine components from excessive wear. However, used oil, having been in service for an extended period, contains impurities that reduce its viscosity. This results in less impact on engine performance and consequently lower fuel consumption. 2. Differences in engine oil: If you switch from 5W30 to 10W40 oil during an oil change, the increased viscosity and poorer low-temperature fluidity will create more resistance in the engine. This leads to higher fuel consumption and accelerated wear.
As a veteran car enthusiast with twenty years of driving experience, I've encountered several instances where fuel consumption suddenly increases right after an oil change. This usually happens because either too much oil was added or the wrong viscosity grade was used. For example, last time I got an oil change, the shop attendant accidentally overfilled the engine oil, increasing internal resistance and causing fuel consumption to spike by ten percent. Fresh oil can also be thicker initially, especially if the wrong SAE grade is used—say, switching from 5W-30 to a heavier 15W-40, which forces the engine to work harder and burn more fuel. Sometimes, it’s not even the oil’s fault—like when I got overly excited after a fresh change and started revving aggressively, naturally guzzling more gas. So don’t panic: first, check the dipstick to ensure the oil level is correct, then drive for a week or two to see if consumption normalizes. If it doesn’t improve, visit a professional shop ASAP—prolonged high fuel consumption harms the engine and drains your wallet. Any sensible car owner knows that regular maintenance is the best way to avoid these slip-ups.
