What are the real experiences of using 5w30 and 5w40 in a Focus?
2 Answers
The manufacturer of this car's engine requires the use of 5w-30 oil viscosity, whether it's mineral oil or synthetic oil. The 5w-40 oil viscosity is not entirely suitable for the classic Focus. Here are the specific differences between 5w30 and 5w40: In terms of stability at high temperatures: The numbers 40 and 30 after 5w represent viscosity. The larger the number, the higher the viscosity and the higher the maximum applicable temperature. This means that 5w40 can adapt to higher temperature environments than 5w30. High-viscosity oil (with a higher value) may also be more suitable for high-speed driving or heavy-load vehicles. In terms of thickness: 5W30 oil is slightly less thick than 5W40 oil, making it more suitable for new cars and new engines. 5W40 oil is thicker and more suitable for older cars, as it can increase sealing and avoid oil burning.
I've been driving a Focus for several years, using it for daily commutes, and have tried both 5W30 and 5W40 engine oils, noticing quite obvious differences. With 5W30, cold starts are exceptionally smooth, especially on winter mornings—the engine runs with minimal noise, and fuel consumption is slightly lower, saving about 0.5 liters per 100 km, making city driving very economical. However, during summer highway driving when engine temperatures rise, the power feels slightly weaker, and the protection seems insufficient. Switching to 5W40, the engine runs quieter and more stable at high RPMs, offering better protection for long-distance driving with noticeably reduced noise. Fuel consumption increases slightly but remains acceptable, around 0.3 liters more. Overall, 5W30 is ideal for daily fuel efficiency and cold conditions, while 5W40 is more durable for hot weather or aggressive driving. I recommend switching oils seasonally and maintaining frequent oil checks to prevent engine wear issues.
