Can You Add Engine Oil to a Hot Car?
2 Answers
You can add engine oil to a hot car. When changing the engine oil, if the vehicle has been parked for a while, it is common to warm up the car before the oil change. Typically, the oil is changed when it has reached a certain temperature. Changing the oil while the car is hot helps to drain the old oil more thoroughly. When the oil is at a certain temperature, it softens some of the sludge inside the engine, allowing these softened deposits to flow out along with the old oil through the drain plug. Generally, idling the car for 3 to 5 minutes is sufficient, and it is most appropriate when the coolant temperature gauge reaches around 90 degrees. Once the car reaches the standard temperature, turn off the engine and let it sit for a short while before draining the old oil. This allows the old oil to settle better into the oil pan. Additionally, draining the old oil immediately after turning off the engine can easily result in burns from the hot oil.
From a maintenance experience perspective, adding oil to a hot engine is really not recommended. The primary reason is safety: after the engine has just been running hot, the oil temperature can reach a hundred degrees or even higher. If you open the hood, oil vapor or hot oil droplets may splash out, potentially burning your skin or eyes. I've personally witnessed such accidents before. Another key issue is measurement accuracy. When the oil is hot, it expands, causing the dipstick reading to be falsely high. If you add oil at this point, the oil level may exceed the upper limit once the engine cools down, leading to excessive internal pressure in the engine, which can damage piston rings or oil seals. I believe it's best to turn off the engine and wait 15-30 minutes before checking the oil level, allowing the engine to cool completely before proceeding. When adding oil, pour it in slowly to avoid spills. In the long run, this habit can extend engine life and reduce unexpected repairs.
