What should you do before you check the level of oil in the engine?

An accurate measurement of the oil level is only possible on a cold, switched-off engine, or a few minutes after it has been turned off. The engine must be switched off because while it is running, oil circulates in the lubrication system, and its level in the oil sump is artificially low. Waiting for a few minutes allows all the oil to drain back into the sump, which guarantees a reliable measurement result.