2026-07-09 · 4 min read
What does 5W-40 mean? Engine oil grades explained
The numbers on engine oil like 5W-40 tell you its viscosity. Using the wrong grade can hurt your engine. Here's how to read the label and pick the right oil.
Ever wondered what 5W-40 or 5W-30 on an engine oil bottle actually means? Those numbers describe the oil's viscosity — how thick or thin it is at different temperatures. Using the right grade matters for protection and fuel economy; the wrong one can affect lubrication. Here's how to read the label.
What the numbers mean
Take 5W-40. The '5W' is the cold rating (W = winter) — the lower the number, the better it flows on a cold start, protecting the engine in those first seconds. The '40' is how thick it stays at full operating temperature — a higher number holds up better when hot. So 5W-40 flows well cold and stays protective hot.
Mineral, semi- or fully synthetic
Beyond the grade, oil comes in mineral, semi-synthetic and fully synthetic. Fully synthetic protects best and lasts longest — ideal for turbo and European engines. But 'better' means the grade and type your carmaker specifies, not simply the most expensive one.
Always follow your car's spec
Your owner's manual lists the exact grade and any approval (e.g. an ACEA or manufacturer spec). Using a grade that's too thick or thin can hurt economy or protection. 4M CARCARE uses the correct-spec oil for your car and advises what suits your driving. Based in Bandar Sri Damansara — WhatsApp us your car model for the right oil.