Does Engine Oil Expand When Hot? Informative Guide

When engine temperature increases a little bit, you will not notice the significant changes in oil level. But, if the lubricant becomes highly heated, its quality can be deteriorated.

Many believe a hot engine might give a false reading because hot engines make oil thinner. Thinner oil will usually increase in quantity. So chances are you may have heard people say oil expands when hot. So does engine oil expand when hot? Let’s find out.

does engine oil expand when hot

Does engine oil expand when hot?

Yes, like most liquids, engine oil expands due to the increases of molecular distance and kinetic energy when exposed to high temperatures. However, while engine oil will expand when hot, it is limited.

The reaction of motor oil to heat is a fundamental trait of its protective role in vehicles. As engine conditions change, a rise in temperature causes motor oil volume to increase. This is why manufacturers provide information on the correct oil range and change intervals.

In the case of synthetic oil, sourced for its stability under various engine conditions, the volume increases more predictably than other lubricants with additives like sorbitol. It is a crucial consideration, especially in weather that contributes to overheating problems. Customers are often alert to this fact, as the majority understand that consistent engine oil temperature is vital to protecting of engine parts and overall vehicle health.

It may start contracting instead of expanding if exposed to an extremely high temperature and becomes too hot. So for those asking, does oil expand when hot? Now you know. But what are the basics behind the expansion of engine oil when hot?

What causes motor oil to expand when hot?

We have stated above that engine oil expands when hot. But what happens when engine oil gets too hot? Liquids have molecules. So when exposed to heat, it takes up more between these molecules. As for engine oil, its molecular bonds are weak, so they always give in to heat, resulting in expansion.

And the theory behind this is thermal expansion caused by kinetic energy. While thermal expansion is an increment in the volume of liquid due to heat, kinetic energy is the energy generated during motion. So let’s see how thermal expansion and kinetic energy expand engine oil when exposed to heat.

While our cars are driven, the engine gets hot. And at this point, the oil in the oil pan goes through the oil filter and circulates to all moving engine parts that need it. However, while these parts keep moving, they get hot, invariably heating the engine oil. Sometimes you will notice more smoke from car due to engine overheating.

The energy generated by these moving parts (kinetic energy) gets converted into heat energy and increases the engine’s temperature. This motion and increase in temperature allow the oil to flow effortlessly. Hence, creating a kinetic energy space between the molecules of the engine oil causes the oil to increase.

Does engine oil level increase when hot?

Can you put oil in your car when it’s hot? Engine oil has a weaker molecular bond than solid, making them melt faster and thinner when heated. The lighter they are, the more the quantity. So yes, as engine oil gets hot, its level increases though the difference isn’t that much. This is why most people often opine that you check your oil level when the engine is cold.

Cold oil will tell you the exact level and help you avoid burns a hot engine might impact. But when the oil is hot, it increases a little, giving a false reading. However, some people still recommend checking the oil when it is hot. So should you check car oil when hot or cold? It depends.

While cold Castrol Oil will give you an accurate reading since it’s in its natural state, checking it when it’s warm might be ideal, especially when checking oil in cold weather. This is true because a freezing oil contract makes it lesser than its supposed state and can also give a false reading.

And if you top the oil to its max in this condition, it might get past the max line.

when the engine becomes warm and pours down the oil pan.

Is it normal for oil dipstick to be hot?

As you drive your car, the engine oil runs through the engine parts to lubricate and cool them. Since the oil collects heat, it becomes hot.  Because the dipstick also sits in the oil, it is normal to be hot. However, it should also cool down as your engine cools down.

Does oil expand when cold?

Oil does not expand when cold. In cold temperatures, oil gets denser or thicker.  This is one reason you experience a slow flow of oil across engine parts when it’s cold, which often limits car performance. Oil contains the coefficient of expansion and can only expand when it’s hot, not cold.

How to check your engine oil level?

check engine oil when hot or cold

Checking oil levels is the best way to ensure you’re running with your oil at the right level. This ensures all engine parts get the correct quantity of oil when needed, which aids optimal performance. So here is an easy way to check your oil level.

  • Park your car on leveled ground. An uneven surface might lead to a false reading.
  • Locate your dipstick; this is usually at your engine bay.
  • Take out the oil dipstick and wipe off the oil with a clean cloth.
  • Return the oil dipstick and pull it out again. The oil level should be between the maximum and minimum mark but very close to the maximum mark as possible.

While this might be quite an easy job, many are often confused about the appropriate time to check oil levels for accurate results. The question is, should I check engine oil when hot or cold or can you put oil in a hot car?

You can check it when it is cold; you will get a good result since it’s in its original state and the oil has had time to settle in the oil pan. Also, check it when cold for safety reasons, especially if you’re not too inclined with cars. This is to avoid burning yourself from hot engine components.

However, you can also check it when the engine is warm, especially when it’s freezing outside. If you are doing it during extremely cold weather, let the car run for about 2 – 3 minutes. This will give you a good reading and won’t be hot enough to cause burns. In cases where you just drove the car, allow it to sit for 20 – 30 minutes to avoid burns. If you change engine oil regularly, you will get excellent performance of your car and can avoid unwanted engine noise.

How much does engine oil expand when heated?

Engine oil typically has a volumetric thermal expansion coefficient in the range of 700×10−6700×10−6 to 950×10−6950×10−6 per degree Celsius. To provide a specific example, let’s use a mid-range value of 825×10−6 °C−1825×10−6°C−1.

Let’s calculate the expansion for a specific scenario:

  1. Suppose you have 1 liter (1000 milliliters) of engine oil.
  2. If the temperature increases by 50°C (a common temperature change for engine oil when the engine is running), the volume change can be calculated as follows:



  • V0​ is the initial volume (1000 milliliters)
  • β is the thermal expansion coefficient (825×10−6 °C−1) ΔT is the temperature change (50°C)   Thus, ΔV = 1000×825×10−6×50 = 41.25 milliliters So, the engine oil would expand by approximately 41.25 milliliters when heated from its initial temperature by 50°C. This is a general estimate and can vary slightly based on the specific type of engine oil and its exact thermal expansion coefficient.

What happens to engine oil at high temperature?

Does oil expand when hot? At high temperatures, engine oil undergoes several changes that can affect its performance and the overall health of the engine. Here are some key effects of high temperatures on engine oil:

  1. Viscosity reduction: As the temperature increases, the viscosity (thickness) of the engine oil decreases. This can reduce the oil’s ability to form a protective film between moving parts, leading to increased friction and wear.
  2. Oxidation: High temperatures accelerate the oxidation process, causing the oil to break down and form sludge, varnish, and other harmful deposits. Oxidation reduces the oil’s effectiveness and can lead to engine deposits that impair performance.
  3. Volatility: At high temperatures, engine oil can evaporate more quickly. This can result in a loss of oil volume, requiring more frequent top-ups and potentially leading to inadequate lubrication if not addressed.
  4. Thermal degradation: Prolonged exposure to high temperatures can cause the oil’s molecular structure to break down, reducing its lubricating properties. This thermal degradation can lead to the formation of harmful byproducts that further damage engine components.
  5. Additive depletion: Engine oils contain various additives to enhance performance, such as detergents, dispersants, anti-wear agents, and antioxidants. High temperatures can cause these additives to break down or deplete more quickly, reducing the oil’s overall effectiveness.
  6. Formation of deposits: High temperatures can cause the oil to form carbon deposits and sludge, which can clog oil passages, filters, and other engine components, leading to reduced efficiency and potential engine damage.

To mitigate these effects, engine oils are formulated with high-quality base oils and additives designed to withstand higher temperatures. Using the appropriate grade of oil specified by the engine manufacturer and ensuring regular oil changes can help maintain optimal engine performance and longevity.

At what temperature does engine oil begin to break down?

Engine oil begins to break down at temperatures typically above 250°F (121°C). However, the exact temperature at which breakdown occurs can vary based on the formulation of the oil and the presence of additives. Here are some key points to consider:

  1. Conventional engine oils: Conventional mineral-based engine oils generally start to degrade and oxidize significantly at temperatures above 250°F (121°C). Prolonged exposure to these temperatures can cause the oil to lose its lubricating properties, leading to increased engine wear and sludge formation.
  2. Synthetic engine oils: Synthetic oils are designed to withstand higher temperatures and typically have a higher thermal stability compared to conventional oils. They can often handle temperatures up to 300°F (149°C) or higher before significant breakdown occurs. This makes them more suitable for high-performance and high-temperature applications.
  3. Oxidation and thermal degradation: At high temperatures, engine oils undergo oxidation, which leads to the formation of acidic compounds and sludge. Thermal degradation also occurs, breaking down the molecular structure of the oil and reducing its effectiveness.
  4. Additives: Engine oils contain various additives that enhance their performance, such as antioxidants, detergents, and anti-wear agents. These additives can help protect the oil from breakdown at higher temperatures, but they too can degrade over time and with excessive heat.
  5. Engine operating conditions: Engine operating conditions, such as prolonged idling, towing, and high-speed driving, can increase the engine’s temperature and accelerate oil breakdown. Regular oil changes and using the appropriate grade of oil for your vehicle can help mitigate these effects.

In summary, while conventional engine oils generally begin to break down at temperatures above 250°F (121°C), synthetic oils can often handle higher temperatures. Monitoring engine temperature and ensuring regular maintenance can help prolong the life of the engine oil and maintain optimal engine performance.

Does oil shrink in cold weather?

Yes, oil does shrink in cold weather due to thermal contraction. As the temperature decreases, the volume of the oil decreases as well. This is a common physical property of most liquids, including oil. The extent of the shrinkage depends on the specific thermal expansion coefficient of the oil.

Here are a few key points regarding oil behavior in cold weather:

  1. Increased viscosity: At lower temperatures, oil becomes more viscous (thicker). This can make it harder for the oil to flow through the engine, leading to increased friction and wear during start-up and operation in cold conditions.
  2. Reduced volume: As the temperature drops, the volume of the oil decreases slightly. This shrinkage is usually not significant enough to cause problems in an engine or other systems, but it can affect precise applications where exact volumes are critical.
  3. Thermal expansion coefficient: The thermal expansion coefficient for oils typically ranges from 650×10−6650×10−6 to 950×10−6950×10−6 per degree Celsius. For example, if the temperature drops by 10°C, the volume of the oil will decrease by about 0.065% to 0.095%.


This article has answered the question, does engine oil expand when hot? A recap! Yes, it does expand because engine oil has weak molecular bonds that easily give in to heat. Thus, ultimately increasing the oil level a bit. One must be careful when checking engine oil levels to avoid a false reading.

You will get a good result when the oil is cold. Also, check when it’s cold, especially if you’re not experienced with cars, to avoid burns. However, you can also check it when it’s warm. So why check engine oil when warm? You will get a better result, especially when it’s freezing outside. Note that a warm engine is entirely different from an extremely hot engine.

Solomon Osuagwu

Osuagwu Solomon is a vetted auto mechanic with over ten years of experience in the garage and five years of experience as a service writer. He prides himself in writing accurate information on professional repair guides, DIY repair guides, buyer’s guides, comparisons, and car reviews. If he’s not in his repair garage, he’s writing automotive blogs to help car owners and fellow mechanics to troubleshoot and proffer solutions to several car problems.

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