Should Older Cars Use 5W30 or 5W40?

[DiValentina]

For older cars, whether to use 5W30 or 5W40 generally depends on the engine's condition and cylinder wear. Older engines often require oil to assist in sealing, so 5W40 is usually recommended. However, the specific choice should consider the vehicle model, the environmental temperature of the region where the car is used, and the oil type recommended in the vehicle's maintenance manual. More detailed information is as follows: 1. There are many types of oil grades, and different grades indicate different oil performances. Taking 5W-30 as an example, the '5' represents that the oil is suitable for temperatures above -25°C. If it's '10', it means above -20°C. The smaller the number before the 'W', the better the low-temperature fluidity. This makes it more suitable for northern winters, offering better cold-start performance. 'W' stands for winter, indicating that the oil has a wide applicable temperature range and can be used all year round. 2. The number after 5W-30 is the viscosity index, which refers to the oil's viscosity at 100°C being 30. The larger the number, the higher the viscosity, providing better protection for the engine at high temperatures. However, the appropriate oil grade should be chosen based on different driving conditions and vehicle models. 3. The main differences between 5W30 and 5W40 are: 5W-30 has relatively better fluidity, more effectively reducing fuel consumption and allowing the engine to dissipate heat faster and more efficiently. However, for some older cars, using 5W-30 may result in slightly louder engine noise, and some engines that strictly require 5W-40 may experience higher than normal fuel consumption if 5W-30 is used instead. At high temperatures, 5W-40 offers better oil stability.

[StAngelo]

As the owner who's watched this old companion run for fifteen years, I can say the parts in the engine bay have all gotten a bit loose. Using 5W30 made winter starts smoother, but during summer highway drives, the oil pressure always hovered on the low side. A seasoned mechanic opened up the engine and showed me—the gap between the piston rings and cylinder walls was nearly twice that of a new car. Now, I use 5W40 year-round, like applying lubricant to joints, and the engine noise after warming up sounds much more solid. Older cars tend to leak from the oil filler hole, and the 40 viscosity helps seal those leaks too. But you’ve got to keep an eye on the dipstick—regular checks are better than a major overhaul.

[McKaden]

Having worked on hundreds of old engines at the auto repair shop, I can say that cars with odometers over 100,000 kilometers are like middle-aged people needing calcium supplements. The 5W40 oil has a higher high-temperature viscosity index, making its oil film more resilient, especially during summer traffic jams. But don't rush to switch—first check the oil pressure warning light on the dashboard. I once had an old Passat owner who insisted on using 5W30, and by 150,000 kilometers, the camshaft had developed scratches. Now, for vehicles over ten years old, I directly recommend 5W40 with an anti-wear additive. Changing viscosity should be a gradual process; mixing different grades can actually harm the engine.

[MartinLynn]

Veterans of classic car modifications understand that cast iron engines from 20 years ago differ from today's all-aluminum blocks. My old BMW E46, equipped with forged pistons, requires 5W40 oil to handle high RPMs. For regular classic cars, the choice depends on driving conditions: 5W30 is fuel-efficient for long-term city crawling, while frequent highway driving calls for 5W40. Here's a simple trick—listen for valve noise during cold starts; a ticking sound indicates the oil is too thin. Older engines often have sludge buildup in oil passages, and overly fluid oil can dislodge debris and clog the filter.