Should the oil dipstick be checked when the engine is hot or cold?
4 Answers
Check the oil dipstick when the engine is cold. Specifically, wait at least thirty minutes after turning off the engine. This is because while the vehicle is running, the oil circulates throughout the engine to lubricate, reduce friction, dissipate heat, clean, and perform other functions. Immediately after turning off the engine (hot state), the oil has not fully returned, which can lead to inaccurate measurements. Precautions for adding engine oil are as follows: 1. Adding engine oil is not like refueling gasoline—filling it to the maximum is not the ideal condition. 2. The correct oil level should be at the middle mark on the dipstick. Overfilling can create resistance for the engine's pistons, increase fuel consumption, reduce power output, and lead to more carbon deposits. Conversely, insufficient oil will fail to provide adequate lubrication and cooling.
I usually check the oil dipstick when the engine is cold. After the car sits overnight, I pop the hood and pull out the dipstick in the morning before starting the engine. At this point, all the oil has drained back to the oil pan, giving the most accurate reading. If you check right after turning off the engine, a lot of oil hasn't drained back yet, and the measurement can be off by more than half a centimeter. Remember to wipe the dipstick clean and reinsert it all the way for a second measurement. Parking on level ground is also crucial – checking on a slope will definitely give inaccurate readings. While you're at it, take a quick glance at the oil color. If it's black like soy sauce, it's time for a change. If it's clear amber, the oil is in good condition. When it comes to car maintenance, paying attention to these details can add several more years to your vehicle's lifespan.
Personally, I believe checking engine oil when the engine is cold is the most reliable method. Last time during maintenance, the technician specifically reminded me not to pull out the dipstick immediately after high-speed driving—not only is it scalding hot, but the reading will also be lower. It's best to wait at least ten minutes after turning off the engine, allowing residual oil in the pipes to gradually flow back. If the car has been sitting overnight (cold engine), it's even better—just pull out the dipstick, wipe it clean, insert it vertically all the way down, then pull it out to check. The ideal oil level should be at about 70% between the upper and lower marks. Also, observe the oil's viscosity; if it's too thin, it might be diluted with gasoline, which could indicate potential engine issues.
The most accurate measurement is obtained when checking the oil level on a cold engine. I usually check it right after refueling, ensuring the engine has been turned off for at least twenty minutes before measuring. Make sure to fully insert and then remove the dipstick, and check the oil mark against the light. If you check immediately after turning off the engine, the oil level may appear lower than it actually is, leading to overfilling if you add more oil. Excessive oil increases crankshaft resistance and can cause long-term engine damage. Additionally, if you notice a strong gasoline smell in the oil, it's important to promptly inspect the fuel injection system.
