Engine Oil: How to Read the SAE Rating and Choose the Right Viscosity
What SAE means on engine oil
When you look at a can of engine oil you see codes like 5W-30, 10W-40, 0W-20. These are codifications established by SAE (Society of Automotive Engineers) defining oil viscosity at different temperatures. Understanding how to read them lets you choose the right oil for your car.
The two viscosities: winter and summer
- The number before W (e.g. 5W) — cold viscosity, W stands for Winter. Lower number = more fluid when cold
- The number after (e.g. 30) — viscosity at 100°C, typical operating temperature. Higher number = denser (more protective) when hot
Practical examples:
- 0W-20: very fluid cold, light hot. For modern low-displacement engines, hybrids
- 5W-30: most common today, optimal compromise
- 10W-40: classic for older or high-mileage engines
- 15W-40: very old engines or heavy use, hot climate
Why following the manufacturer specification matters
Wrong viscosity causes: too fluid (0W-20 where 10W-40 needed): insufficient oil film at high temperatures, increased wear; too thick (10W-40 where 0W-20 needed): increased internal friction, reduced performance.
Beyond SAE: ACEA and API
- ACEA: A3/B4, C2, C3 — European standards for petrol, diesel and DPF-equipped engines
- API: SN, SP, CK-4 — American standards
- Manufacturer homologations: VW 504.00/507.00, MB 229.51, BMW LL-04 — required for in-warranty vehicles
Synthetic, semi-synthetic, mineral
- Synthetic: maximum performance, modern car standard
- Semi-synthetic: good compromise for mid-range cars
- Mineral: only for very old engines
Oil changes: how often
Manufacturer indications range 10,000-30,000 km. In urban use and harsh climate anticipate by 20-30%.
Oil additives: when they help
Additives can: reduce friction (PTFE, ceramic, nano-particles), clean the system (Engine Flush before changes), stop small leaks. Pro-Tec Engine Flush 375ml (pre-change cleaning), Pro-Tec Oil Booster (maintenance), Pro-Tec Nano Engine Protect (anti-friction) can extend engine life.
Conclusions
Reading an SAE code is simple: first number for cold fluidity, second for hot viscosity. Always follow the manual. Pro-Tec range on LS Motors with shipping 24/48h.
