Walk into any parts shop and the oil shelf looks like a maths test. Here's what those numbers actually mean, and which one suits your car on South African roads.
What the numbers mean
The first number with the W is cold-start flow (W for winter). The second is how the oil holds up at operating temperature. So 10W-40 flows like a 10-weight on a cold Gauteng morning and protects like a 40-weight once the engine is hot.
5W-30: modern petrol engines and turbos
If your car is roughly 2010 or newer, has a turbo, or the manual specifies a low-ash synthetic, this is usually your grade. It reaches the top of the engine fastest on cold starts, which is where most engine wear happens. Castrol Magnatec 5W-30 A5 is the everyday pick here.
10W-40: the safe middle ground
The workhorse grade for most petrol hatchbacks and sedans doing school runs and city traffic. Semi-synthetic, forgiving, and well-suited to cars with 100 000 km or more that aren't burning oil. Castrol Magnatec 10W-40 and Shell Helix HX7 10W-40 both sit here.
15W-40: older petrol and light diesel
High-mileage engines and older diesels with wider internal clearances. A thicker cold rating means less oil consumption in a worn engine. Shell Helix HX5 15W-40 is the value option, while Shell Rimula R4 X 15W-40 is the heavy-duty diesel choice.
20W-50: older, hard-worked, hot-climate engines
Classic engines, older bakkies and anything that runs hot in KZN or Limpopo summers. Shell Helix HX3 20W-50 is the traditional multi-grade here.
Three rules before you buy
- Your owner's manual wins over any online advice. Always check the specified grade and spec (API or ACEA).
- Going thicker than specified on a modern engine can starve the top end on cold starts.
- Change the filter every time you change the oil. It's the cheapest part of the job.
Still unsure? Send us your vehicle year, model and engine size and we'll confirm the right grade and quantity before you order.