Is Adding Cold Oil to a Hot Engine Harmful?

QuestionsCategory: Ask An ExpertIs Adding Cold Oil to a Hot Engine Harmful?
Alexander Allen asked 5 months ago
I live in Minnesota where it gets quite chilly, and I carry a quart of oil in my Jeep as these 4.0 engines are prone to leaks. My concern is about pouring oil that's at extremely low temperatures (like 20, 10, or below zero degrees) into the engine when it's fully warmed up. I've heard that rapidly cooling hot metal can cause damage, and I'm wondering if this applies to pouring cold oil into a hot engine. Is this something I should avoid doing, or is it generally safe?
1 Answers
Zack Norman Staff answered 5 months ago
Hey there, Alexander! Great question! Your concern about adding cold oil to a hot engine is a pretty valid one, and one that should definitely be considered for both safety and ensuring that you do this right, especially in colder climates like Minnesota. Let's break down the answer:
  1. Impact of Cold Oil on a Hot Engine: Generally, adding a small amount of cold oil to a hot engine isn't problematic. The engine's heat quickly warms the oil, and because oil doesn't have a high heat capacity compared to water, it doesn't cool the engine parts rapidly enough to cause damage.
  2. Full Oil Changes in Cold Weather: If you're doing a complete oil change in cold weather, it's advisable to drain the oil when the car is hot, allow it to cool down for about 30-40 minutes, and then refill. This helps in managing the temperature differences more effectively.
  3. Warming Up the Oil: A handy tip is to place the oil container under the bonnet for about 10 minutes before adding it to the engine. This can bring the oil to a more moderate temperature, reducing the temperature disparity.
  4. Professional Experience: Many mechanics, including those who have worked for years servicing cars, often add oil to hot engines without waiting for them to cool down. The risk of damage in these scenarios is typically low.
In summary, while it's always good to be cautious, adding a small amount of cold oil to a hot engine, especially in an emergency, is generally safe. However, for full oil changes, managing the temperature difference more carefully is a good practice. Zack - Motor Verso Mechanics Team