At what sub-zero temperature can 15w40 engine oil not be used?

[ManuelLee]

It can be used above -15°C. Below is relevant information: Introduction to engine oil: Engine oil, also known as engine lubricant, serves functions such as lubrication and wear reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion protection, as well as shock absorption and buffering. Engine oil consists of base oil and additives. The base oil is the main component of lubricating oil, determining its fundamental properties, while additives compensate for and improve the shortcomings of the base oil's performance, endowing it with certain new characteristics, making them an important part of lubricating oil. Introduction to grading: The number before W indicates low-temperature fluidity, the number after W indicates high-temperature viscosity, and W stands for winter. Precautions: Higher viscosity does not necessarily mean better engine oil; it's important to choose the right oil for your vehicle. Engine oils should not be mixed.

[DeMicah]

I used to repair cars in the northern regions, where 15W-40 oil becomes ineffective at around -20°C. When winter temperatures drop, the oil thickens, making engine starts particularly difficult or even impossible, which can lead to wear or battery drain. I had a client who insisted on using 15W-40 during a cold snap, and their car wouldn't start, resulting in a tow to the repair shop and costing several hundred dollars. It's advisable to switch to oil with better low-temperature fluidity before winter, such as 5W-30 or 0W-40, especially in areas where temperatures are expected to drop below -15°C. Regularly check the oil condition—don't rely solely on dashboard readings. If you notice difficulty starting the engine, change the oil promptly. Don't try to save money only to end up with bigger problems.

[JoelLynn]

As a long-time driver in snowy conditions, I've personally experienced the limitations of 15W-40 oil. When temperatures drop to -25°C, this oil becomes practically unusable, thickening like syrup and making the engine struggle to turn over. One winter, I tried to save money by not changing the oil and ended up unable to start my car in the early morning, nearly causing serious trouble. Later, I switched to 5W-grade oil, and cold-weather starts became much smoother. Checking your oil is simple: when the forecast predicts around -20°C, proactively change it—don't wait for problems to arise. Oil quality affects your car's lifespan; rather than saving money, choose the right oil to ensure worry-free winter driving.

[DelKatherine]

I've been into car modifications for years, and 15W-40 oil becomes useless below -20°C. The extreme cold drastically increases oil viscosity, making the engine hard to turn over, which can damage the battery or components. I've used this oil before - when temperatures dropped to around -25°C, my car completely refused to start. Switching to thinner oil like 5W is better, ensuring quicker starts and saving battery power. Always check the thermometer during maintenance - if it's below -15°C, change your oil immediately. Don't be lazy about this or you'll regret it.