Maybe you’re driving home this evening and you decide to pull into the petrol station for some fuel. Maybe while the helpful attendant is filling your tank he or she offers to check your oil. Maybe you say yes, pop the hood and watch as said attendant fiddles around with your dipstick. Now maybe you need to top-up becasue the level is low? Maybe.
But checking your oil at the petrol station – after your car’s engine has been running for awhile and has reached its normal operating temperature – is quite possibly the worst thing you can do. Why? Well simply because a lot of the oil will still be up in the engine’s head and not down in the sump (basically the receptacle in which it lives).
This means that the dipstick (noun, a graduated rod for measuring the depth of a liquid), which runs directly into the sump, will give an inaccurate reading: one that will probably see you adding an unnecessary amount of oil to the engine. Yep, you might very well overfill it. And overfilling an engine with oil can be very, very bad.
So what to do then? Well for starters never check your oil at the petrol station. Instead check it first thing in the morning, on a level surface and before starting the engine. That way all the oil will be collected in the sump and you’ll know exactly how much or how little is available to your motor. Got it? Good. – Thomas Falkiner