Should the oil dipstick be checked when the engine is cold or hot?
2 Answers
Oil dipstick can be checked whether the engine is cold or hot, but it is more recommended to check when the engine is cold. Here are the relevant explanations: 1. The difference in oil level between cold and hot engine conditions is generally small, usually only about 2-3 millimeters, which corresponds to a few hundred milliliters of oil, and has little impact on the engine. 2. When the engine is cold, the dipstick shows the total oil capacity of the engine, while when the engine is hot, it shows the amount of oil that meets the lubrication needs of the engine. Generally, if the oil level is above 3/4 of the range between the upper and lower marks when the engine is cold, or above 1/2 of the range when the engine is hot, the oil quantity is sufficient.
As a seasoned driver with twenty years of experience, I always check the dipstick when the engine is cold—right before starting it in the morning. This is the safest approach. After the engine has been off for several hours, the oil temperature drops, preventing expansion, so the dipstick reading accurately reflects the actual oil level. Checking when the engine is hot, like shortly after turning it off, can be misleading because the oil is still warm, flows back into the oil pan, and expands, causing the dipstick to show a higher reading. Adding oil under these conditions can lead to overfilling, which may damage the engine. In my younger days, I made the mistake of checking when the engine was hot and ended up overfilling, causing oil leaks and unnecessary repair costs. Here’s a tip: After parking, wait at least half an hour for the engine to cool down, then pull out the dipstick, wipe it clean, reinsert it, and check the oil level to ensure it’s between the upper and lower marks. Make it a habit to check regularly—say, once a week—to prevent oil shortages that could lead to serious issues like engine seizure, which helps extend your car’s lifespan. In short, checking when the engine is cold is the best practice—safe and accurate.
