Does switching from 5w30 to 5w40 affect the engine?

[DiJaxon]

Switching from 5w30 to 5w40 does not affect the engine. Engine oil, also known as engine lubricant, serves multiple functions such as lubrication and wear reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion protection, as well as shock absorption. It is often referred to as the "blood" of a car. Below are the key functions of engine oil: Friction reduction: A sufficiently thick oil film separates the surfaces of moving parts, thereby minimizing wear. Sealing: Engine oil forms a seal between the piston rings and pistons, reducing gas leakage and preventing contaminants from entering. Rust prevention: Lubricant adheres to part surfaces, protecting them from water, air, acidic substances, and harmful gases. Shock absorption: When pressure in the engine cylinder rises sharply, suddenly increasing the load on pistons, piston rings, connecting rods, and crankshaft bearings, the lubricant transmitted through the bearings helps cushion the impact. Cleaning: High-quality engine oil carries away carbon deposits, sludge, and metal wear particles from engine components back to the oil pan, flushing away contaminants generated on the working surfaces through oil circulation.

[SanLeilani]

After switching from 5W30 to 5W40 oil last time, I clearly noticed a slight increase in fuel consumption—about 0.5 liters more per 100 kilometers. However, during summer long-distance drives, the engine ran more steadily with reduced noise and was less prone to overheating under high temperatures. The problem arises in winter: cold starts become sluggish, requiring more effort from the battery, and prolonged use may accelerate internal engine wear. In truth, changing oil viscosity isn’t particularly risky—it depends on driving conditions. For hot regions like Hainan, 5W40 offers better protection; in colder northern climates, 5W30 ensures smoother starts. Always remember to check the dipstick regularly and avoid unnecessary viscosity changes.

[VonJasmine]

The numbers in oil viscosity, the first one indicates low-temperature fluidity, with 5W representing easier engine starts in winter. The second number, 40, is slightly thicker than 30, forming a thicker oil film at high temperatures to reduce wear and the risk of oil leakage. After switching to 5W40, the engine performs stronger under high-temperature and high-load conditions, such as being quieter and more durable during highway driving or towing heavy loads. However, initial cold-start friction increases, fuel consumption may slightly rise, and long-term use could affect component lifespan. It's recommended to first check the vehicle manual for the recommended range, as different engine designs match differently. Avoid switching arbitrarily to prevent more harm than good.

[McSamuel]

Driving in icy conditions, I've always used 5W30 oil for quick and effortless starts. Once I switched to 5W40, there was noticeable startup delay in sub-zero temperatures, engine knocking sounds, and slightly increased fuel consumption. Switching back to southern warm weather felt much better with upgraded high-temperature protection and excellent lubrication. Simply put, oil changes don't make a huge difference, but should match the climate—don't arbitrarily increase viscosity in cold regions, while considering it in tropical areas. Oil grade precision matters more—don't risk damaging a big engine to save small money.

[JeffreyLee]

Be cautious when switching oil from 5W30 to 5W40 as it becomes thicker. During initial cold starts, engine components will experience increased rotational resistance, raising the risk of initial wear and higher fuel consumption. Over time, the oil pump will need to work harder, slightly reducing overall engine efficiency. However, the improved high-temperature protection is beneficial, especially for older vehicles or those frequently used for long-distance driving. Avoid making changes unless specified in the manual or recommended by a technician to prevent shortening engine lifespan. Regular maintenance with quality oil is key—minor viscosity changes are acceptable, but avoid frequent switching.