What is the viscosity of engine oil for Japanese cars?
2 Answers
For Japanese car engines, 40 viscosity engine oil is too thick and not conducive to the normal operation of the engine. Most Japanese cars require the use of 30 viscosity engine oil. Hazards of excessively high engine oil viscosity: When the engine oil viscosity is too high, it becomes difficult to start the car at low temperatures. Due to the high viscosity of the oil and the relatively low surrounding temperature, oil circulation slows down, resulting in poor lubrication. This also increases wear and tear on engine components, making it necessary to properly warm up the car in colder temperatures. Poor cleaning performance: If the engine oil viscosity is too high, its circulation speed within the engine will be slower, and it will pass through the filter fewer times. This leads to poor cleaning effects, as the oil cannot promptly carry away wear debris. Over time, the engine is more likely to develop faults. Poor cooling performance: High-viscosity engine oil flows relatively slower. Within the same timeframe, lower-viscosity oil flows faster and can carry away more heat from friction surfaces. Poor cooling can cause the engine to overheat.
I've been repairing cars for over a decade and often see Japanese car owners asking about oil viscosity. It's really not complicated. Japanese cars generally perform best with 0W-20 or 5W-30 oil, especially brands like Toyota and Honda - that's what their manuals typically specify. Why these grades? Because Japanese engines have high precision manufacturing, and low-viscosity oil allows the oil pump to circulate it more easily, reducing friction for better fuel efficiency and component protection. But don't arbitrarily switch to higher viscosity oils - I've seen cases where using 10W-40 actually clogged oil passages and caused engine knocking. You should also consider the specific model and year - newer vehicles mostly recommend 0W-20, while older models might run more reliably on 5W-30. Climate matters too - here in northern China, I've noticed cars start much smoother in winter with 0W oil. Bottom line: don't cut corners with cheap oil. Check your owner's manual or get OEM oil at the dealership - it's the safe, durable choice. After all, your car is your partner - proper maintenance means longer service life.
