Does Engine Oil Expand When Hot?

A temperature rise brings several changes in automotive lubricants. As long as it’s in the safe range, there’s nothing to worry about. But in case the fluid gets extremely heated, then it may result in internal and external damage. 

The most common trait of a hot lubricant is that its viscosity becomes thinner. And another one is that the volume increases.

So, does engine oil expand when hot?

Yes, engine oil expands due to the increase in kinetic energy and distance between the molecules when heated. And as the temp goes up in the lubricant, different stuff happens. Let’s know more below. 

Thermal Expansion Of Engine Oil 

Temp rise is common whenever it comes to the automotive engine. It can be due to weather or the machine itself. The friction of moving parts is one of the sources of heat. So, when we drive, the parts get hot, and so is the lubricant in the pan which flows to different areas through the filter to run smoothly. Here, the energy created by the movement of engine parts gets converted into thermal energy and increases the lubricant’s temp. 

Now, what happens to engine oil when heated? Motor oil expands just like any liquid would at high temperatures. Since such a lubricant is liquid, the intermolecular interactions are fairly weaker. For that, the kinetic energy of those mobile molecules and the space between the atoms increase as the fluid is heated. This results in the expansion of engine oil. Meanwhile, the viscosity of oil decreases too. 

Although the change in oil level is somewhat noticeable, we suggest that you avoid checking it immediately after stopping the vehicle. Otherwise, you may hurt yourself and your engine. Also, this won’t give you the correct measurement. 

Volume Of Engine Oil Expansion At High Temperature

How much does oil expand when heated? Engine oil expands approximately 4.8% more volume per 120°F when hot. The calculation is based on the volumetric coefficient of expansion of unused motor oil i.e. 0.0004/°F. However, the size of expansion isn’t definite as it varies in the temperature, type, and condition of the lubricant. For instance, synthetic oil expands more than mineral ones when it’s hot.

If you want to know the expansion, you can check the change in engine oil level through a dipstick test. However, make sure to wait for around 10 minutes after stopping the vehicle so the lubricant gets back to normal temperature. This will help give you an accurate idea about the oil level in your vehicle. 

Effects Of Engine Oil At High Temperature

Hot engine oil not only does expand but also creates unwanted situations. Here are what happens to your engine oil at high temps. 

• The lubricant becomes diluted or less viscous. 
• Severe friction creates noise and causes damage to moving parts.
• Quicker consumption of oil. 
• Formation of sludge and sediments.
• Risk of leakage. 

Frequently Asked Questions

1. Does Engine Oil Shrink In Cold Weather?

Yes, engine oil would shrink in cold weather just like it can expand at high temps. The molecules of lubricant will get a little closer to each other causing the oil to shrink. Additives like viscosity improver contract during winter and make the fluid more viscous than it should be. As a result, the flow of engine oil gets slower while the pump puts the fluid under pressure forcing it to run through the filter. 

2. At What Temp Does Engine Oil Break Down?

Engine oil can break down at over 300°F. However, it depends on the lubricant type. Conventional motor oil can tolerate up to 250°F and start degrading as it goes past 275°F. Contrariwise, synthetics can withstand up to 450-700°F since they have higher level of tolerance. 

However, you should try to keep the lubricant temperature between 240 and 270°F based on what you’re using. 

3. Does Synthetic Oil Burn Slower?

Yes, synthetic oil has additives that help it burn slower than conventional ones. It contains agents made of sorbitol and carboxylic acid that cause the seals to swell so that it prevents leakage and burns oil slowly. 

Moreover, synthetic oil comes with uniform molecules that ensure the right level of viscosity at different temperatures to make the fluid flow smoothly without excessive burning. 

Final Words

Severe expansion of engine oil is never good. Why? Because extreme hot oil can make things worse as we stated. So, you should try to keep the lubricant within 240-270°F. 

How can you maintain the temperature of engine oil? Just following some simple tricks can keep the lubricant at recommended temp range. Avoid towing heavy stuff, driving aggressively, and extended idling. Use high-quality lubricant and change the oil or the filter as per the manufacturer. Also, check the level of oil regularly. 

Related Post:

• Does Engine Oil Absorb Heat?
• What Is Boron Used For In Motor Oil?
• Does Synthetic Oil Reduce Oil Consumption?