IIRC 30 weight oil is only good for up to 30°C. I try not to use anything lower than 40 weight for my cars.


Source: Rymax Lubricants Holland

Also with our climate the "W" rating doesn't matter at all. It represents the oil flow at 0°F (-17.9°C).

If SAE 30 is good for 5°C to 30°C, 5W30 extends the lower operating range to -35°C. It's irrelevant to us.