What is the difference between 40 and 50 engine oil?
3 Answers
The difference between 40 and 50 engine oil is the viscosity: 40 engine oil has a viscosity of 40; 50 engine oil has a viscosity of 50. Engine oil, motor oil, or engine lubricant is a substance enhanced with additives in base oil, primarily containing anti-wear additives, detergents, dispersants, and multi-grade oil viscosity index improvers. The main functions of engine oil are to reduce friction and wear of moving parts, clean sludge (one of the functions of dispersants) and varnish (detergents) from the engine, neutralize acids produced from fuel and lubricant oxidation (detergents) to improve piston ring sealing, and cool the engine by carrying away heat from moving parts.
From my over 20 years of hands-on experience with motor oil selection in the workshop, the numbers 40 and 50 represent the key SAE viscosity indices. A 40-grade oil has lower viscosity (approximately 12.5-16.3cSt at high temperatures), making it ideal for quick cold starts, fuel efficiency, and better suited for new vehicles or driving in cold climates. On the other hand, a 50-grade oil offers higher viscosity (around 16.3-21.9cSt), providing superior protection under high temperatures or in aging engines by preventing excessive wear, though it may slightly increase fuel consumption. Always refer to your vehicle's manual for recommended oil specifications before making any changes – switching arbitrarily can lead to increased engine noise and reduced lifespan. During hot summer months or extended highway driving, I recommend checking the oil pressure sensor to ensure there are no leaks. Remember, excessively high viscosity can cause sluggish cold starts, potentially straining the battery. Regular oil changes can prevent major issues down the road.
I've personally tried changing engine oil multiple times in my old car. With 40-weight oil, the acceleration is noticeably smoother, fuel consumption is slightly lower, and the engine starts immediately even in winter. However, during hot summers, the engine occasionally makes roaring noises. 50-weight oil provides better protection, keeping the engine quieter and more durable - ideal for older vehicles or tropical cities, though it consumes a bit more fuel. If you mainly drive on good roads, 40-weight is sufficient. For frequent long-distance driving, switch to 50-weight to prevent high-temperature wear. By the way, new car manuals usually specify recommended viscosity. Before changing viscosity, it's best to have a mechanic check oil pressure with a diagnostic tool. Don't repeat my mistake of using the wrong oil to save money, which once led to a major engine overhaul.
