Posted on 11/28/2025
Oil ages even when the car hardly moves. Additives lose strength, moisture, and fuel traces linger after short runs, and tiny acids form. None of this wrecks an engine overnight, but months of sitting can turn good oil into tired oil that protects less on cold start. That is why owners’ manuals list time-based intervals along with mileage. What Happens To Oil While the Car Sits Fresh oil is a blend of base stock and additives that fight wear, rust, and sludge. As the car sits, moisture from normal combustion condenses in the crankcase. If the engine never warms fully, that moisture does not boil off. Small amounts of fuel from rich cold starts can stay mixed in, thinning the oil film. Meanwhile, oxygen slowly reacts with the oil, a process called oxidation. Oxidized oil gets darker and thicker, and its additives cannot neutralize acids as well. Why Short Trips Are Hard On Parked Cars If you only start the car to move it around the driveway o ... read more