Does Engine Oil Expand When Hot? Get The Facts

As a car owner, you may have been curious whether engine oil expands when heated. Understanding why engine oil should be checked during hot temperatures rather than cold can be beneficial when checking your oil level.

When your vehicle is operating at high temperatures, the lubricant in its system will thin out and become less effective. This causes excessive friction which could eventually result in engine damage or malfunctions.

Why is it Said That Engine Oil Expands When Hot?

Like most liquids, engine oil expands when heated. This occurs because the kinetic energy created by movement of parts is converted to heat energy.

The motion of these parts creates a kinetic energy space between molecules of the lubricant, which causes it to expand in size. This allows oil to flow easily through any required parts at any given time.

Engine oil is composed of base oils and additives that work together to lubricate, protect and drain built-up heat from your car’s engine. These include chemicals which act as detergents, friction modifiers, antioxidants, corrosion inhibitors and viscosity index improvers.

Does Engine Oil Expand When Hot?

Does Engine Oil Expand When Hot

The short answer is yes, engine oil expands whenever it is exposed to high temperatures.

Driving our car increases the temperature of its engine, which causes the oil in its pan to flow more freely to areas that need it most for smooth running.

But when the oil is heated, its weak molecular bonds allow it to expand slightly and increase in volume. While this can give an indication of increased levels, we always advise waiting a short while before checking engine oil after driving your car as expansion is only temporary and cannot provide an exact measurement.

Apart from that, it’s essential to recognize that different oils have varying expansion and contraction rates depending on their temperature exposure. This can make the difference between an accurate reading and a false one when checking engine oil levels.

Read More: Can Engine Oil Be Used in a Chainsaw

What Causes Engine Oil to Expand When It is Heated?

Engine oil is a liquid used in your car to help regulate engine lubrication and flow. It’s composed of various materials with added additives for the ideal performance in your vehicle.

Engine oil plays a vital role as an effective coolant. Its thermal properties enable it to transfer heat efficiently and safely from your car’s engine to the air around you.

Just like any other liquid, lubricants can expand when exposed to high temperatures. This occurs because the kinetic energy of those mobile molecules and the space between them increases when the lubricant gets heated.

Is it Normal For Oil Dipstick to Be Hot?

Your car’s engine oil is hot as it travels through it to lubricate and cool parts. So, it is best to keep in mind that the dipstick sits in this fluid, collecting heat in the process. However, it will get cool down as soon as your engine cools down.

Does Oil Expand When Cold?

No your oil will not expand when cold. The thing is that in cold temperatures, the oil gets denser or thicker. This is one of the reason why you’ll experience a slow flow of oil across the engine parts when it is cold, which often affects the performance of your car. Oil is said to contain the coefficient of expansion and is only capable of expanding when it is hot.

How to Check Your Engine Oil Level

To check the oil in your car, first you should ensure that your car is parked on a leveled surface. Now you can go ahead and shut off the engine, then open the hood. Now, locate the dipstick by pulling its metal loop or grip out of its stalk.

Wipe the end of the dipstick clean with a cloth or thick paper towel before reinserting it into its stalk until fully seated.

Now check the oil level again on the dipstick by looking at its end, where you should see either it below or above a line that displays “Low” and “Full.” In some cases, there may be holes instead of markings; in such cases, check that all oil is within an intersecting crosshatched area.


Engine oil is a liquid solution that protects and cools the inner parts of your car’s engine. It consists of two primary components – base stock and additives. The additives help lubricate, while the base stock controls viscosity, lubricity, as well as eliminating built-up heat.

Engine oil expands when heated due to the absorption of kinetic energy from engine parts motion, making it hotter. As a result, you may notice some space between oil molecules when your dipstick is warm – this explains why engine oil appears slightly puffy on cool days.