As you can see from the chart above the first number is the low temperature range and the second number is the high temperature range. The higher the number after the W means it can handle higher temperatures. So the next question is how hot does an engine get?
For most cars, the normal operating engine temperature is in a range of 90 -950 Celsius, but most dashboard temperature gauges don’t show an exact teperature. As the temperature increases the radiator fan will kick in to start cooling the engine. To put it into perspective when you boil your kettle. The boiling point is (not to get too technical) about 1000 C. If your car overheats or you need to top up with water and you have been driving your vehicle do not open the radiator or expansion bottle cap as the water will be hot and will burn you. Wait for the water in the radiator to cool down before filling up with cold or normal temperature water.
SAE 30, 40 or 50 is monograde oil. This oil is no longer used in the latest car engines, but may still be used in some vintage and antique engines. SAE 30 is often used in small air-cooled engines in lawnmowers, garden tractors, chain saws and portable generators.
Do not over fill your engine with oil.