The No-Nonsense Guide for Automotive Workshops & Garages on Automotive Grades

Most modern engine oils are “multigrade,” engineered to protect your engine in both freezing cold and scorching heat. You’ll see them labeled with two numbers—like 5W-30. But what do those numbers actually tell you?

The “W” Number (Winter):This is all about cold starts. The lower the “W” (e.g., 0W, 5W, 10W), the better the oil flows when your engine is cold—helping it reach critical components quickly and reduce wear during those first few seconds after ignition.

The High-Temperature Number:The second number (30, 40, 50) represents the oil’s viscosity at normal engine operating temperature (typically 100°C). A higher number means the oil stays thicker under heat, providing a stronger protective film when your engine’s working hard.

Can You Use a Different Grade Than Recommended?

Your vehicle manual will list a recommended grade, but many manufacturers approve a range of options depending on climate and usage.

Adapting for UK Winters:If you’re struggling with sluggish starts in sub-zero temperatures and your manual allows it, switching from a 10W-40 to a 5W-40 can make a real difference. Both protect equally when hot, but the 5W flows much faster on cold mornings—minimizing engine wear.

Adjusting for Summer or Heavy Loads:Planning a long haul or towing in hot conditions? If your manufacturer permits, moving from a 5W-30 to a 5W-40 delivers a more robust oil film that won’t thin out under extreme heat and stress.

High-Mileage Engines:Older engines sometimes benefit from a slightly thicker oil (e.g., 5W-30 to 10W-40) to help seal internal clearances and reduce consumption. Only do this if the oil still meets your vehicle’s required specs.

The Golden Rule: Approvals Trump Everything

Here’s what most people overlook: viscosity is only half the story. A 5W-30 oil approved for Ford could damage a modern Volkswagen or BMW. Why? Because modern engines have sensitive after-treatment systems (like DPFs and catalytic converters) that demand specific chemical formulas.

·      OEM Approvals (e.g., VW 507.00, MB 229.51): These are the gold standard—manufacturer-tested and certified for your engine. Always match the approval code to protect your warranty.

·      Industry Specs (ACEA, API): These define the oil’s chemical makeup. For example, “Low SAPS” oils are vital for cars with DPFs to prevent clogging.

Quick Checklist: How to Choose the Right Oil

1.        Check Your Manual: Look for approved grades and see if seasonal variations are allowed.

2.        Match the Approval: Always use oil that meets the exact manufacturer code (e.g., Ford WSS-M2C913-D).

3.        Consider the Climate: Choose the right “W” or high-temp number for your environment—within the approved range.

Need help choosing the right oil for your vehicle or machinery?We supply a variety of premium brands and provide expert advice to ensure you get the best match for your requirements. Contact us today:

·      Email: sales@uklubricants.com

·      Phone: 07895 729018 / 07903 808941

Our team is available 24/7 to support your business with real-world expertise—no guesswork, just honest answers.