The direct answer to whether a car needs to be running when changing oil (meaning during the draining and refilling process) is no. The engine should be turned completely off and cooled slightly before you begin draining the old oil and adding new oil.
However, it is commonly advised to run the engine briefly before starting the oil change procedure.
Warming Up Your Engine Before an Oil Change
According to common advice, including guidance from October 2, 2022, "It's also advisable to start the engine and let it warm up for 2-3 minutes, as this helps the oil heat up and allows it to drain more easily."
- Why warm up? Engine oil becomes less viscous (thinner) when warm. This allows it to flow out of the oil pan more completely and quickly, carrying with it more contaminants and sludge that may have settled at the bottom.
- How long? As suggested, running the engine for just a few minutes is usually sufficient to warm the oil without making components excessively hot and unsafe to handle.
The Importance of Turning the Engine Off During the Oil Change
Once the engine is warmed up, it is critical to turn it off before proceeding.
- Safety First: This is the primary reason. A running engine has moving parts (like belts and fans) and extremely hot components (exhaust system, engine block) that pose significant risks of injury or burns.
- Complete Drainage: With the engine off, all the oil will settle back into the oil pan, allowing for a more thorough drain. If the engine were running, the oil pump would be circulating oil throughout the engine, preventing it from draining completely from the pan.
- Accurate Refill: Adding new oil to an engine while it's running can be dangerous due to splash-back and makes it difficult to accurately measure the correct fill level.
Process Snapshot: Engine State During Oil Change
Here's a simple breakdown of the engine's state during different phases of an oil change:
| Activity | Engine State | Primary Reason |
|---|---|---|
| Before (Prep) | Running (Briefly) | Warm oil for easier draining |
| During (Draining) | Off | Safety, complete drain |
| During (Filter Change) | Off | Safety, prevents spills |
| During (Refilling) | Off | Safety, accurate measurement |
| After (Check/Finish) | Off (Initially), then Running (Briefly) | Allows oil to settle, checks level |
In summary, while a brief warm-up before the change is recommended for better drainage, the car's engine absolutely must be off during the actual oil draining and refilling steps.
