Is using 10w40 oil for a new car a big deal?

[DelJulianna]

As long as it meets the viscosity specified by the original oil, using 10w40 oil is not a problem even for a new car. The characteristics of 10w40 oil and recommended oils for cold conditions are as follows: Characteristics of 10w40 oil: Compared to 10w30, 10w40 oil has higher viscosity and better sealing properties, but the engine will consume more fuel. At idle, higher viscosity oil results in lower noise, while under driving conditions, higher viscosity oil leads to higher noise. Lower viscosity oil, on the other hand, is more fuel-efficient. Recommended oils for cold conditions: If SAE10W30 or higher viscosity engine oil is used in cold weather, the engine may be difficult to start. Therefore, it is recommended to use SAE0W20, 5W20, or 5W30 engine oil. Comparatively, using 0W-20 oil can maximize fuel savings.

[LePenelope]

Using 10w40 oil for a new car is indeed not very appropriate. I've seen many cases where the engine sound becomes noticeably muffled after mistakenly using high-viscosity oil during the first maintenance of a new car. New engines have smaller clearances, and thick oil like 10w40 flows slowly at low temperatures, causing more metal friction during cold starts. The difference isn't obvious during highway driving, but in city traffic when the oil temperature doesn't rise sufficiently, it actually increases component wear. Most critically, fuel consumption is affected—actual tests show it burns half a liter more than 0w20 oil, and carbon deposits form faster. For the first two years of a new car, it's best to stick to low-viscosity oil as recommended in the manual. Only consider high-viscosity oil after the piston ring clearance increases past 100,000 kilometers.

[VonAllison]

As a frequent construction site visitor, I've used 10W40 in my pickup for three years. But it's really not recommended for new cars, especially turbocharged ones. Last week, I helped a neighbor inspect his new SUV – the repair shop mistakenly used 10W40, and after just 3,000 km, it had 30% more sludge than the same model. High-viscosity oil pumps slowly at low temperatures, delaying oil flow into the tiny turbo bearing gaps, extending dry friction time. During summer traffic jams with AC on, the coolant temp needle almost hit the red zone while oil temp was just 80°C. Modern engines have narrower oil passages – it's like pumping honey through blood vessels, definitely not smooth.

[StellaLee]

Using 10w40 in a new car may not show immediate issues, but don't overlook warm-up time. The hybrid in my garage roared for the first five minutes with 10w40 in winter, vibrating 30% more than with 0w20. The dealership's diagnostic showed cold-start wear values immediately spiking into the red. Start-stop systems suffer even worse—each restart feels like dry grinding. Modern cars have variable valve timing; thick oil makes VVT response sluggish, with half-second throttle delays that make driving downright frustrating.