Understanding Of Flash Point Of Motor Oil

engine oil flash point

The flash point is the lowest temperature at which a fluid forms enough vapor to ignite. It occurs when it comes into contact with some ignition source. Maximum gasoline oils have a 380°F flash point, while diesel oil temperature is up to 410 °F.

This temperature needs to be higher for all engine oils to prevent pre-ignition. The addition of contaminants lowers the flash point of the oil over time. Let’s get to know what is the flash point of motor oil and other oils.

About Of Engine Oil Flash Point:

All liquid flash points depend on their specific application. For example, paraffin-based fluids with densities between 860 and 890 kg m-3 have flash points typically between 200 and 280°C.

In contrast, naphthenic base liquids have a maximum flash point of 235°C. But engine oils are exposed to high temperatures and contain higher flash points.


Most oils have a minimum flash point temperature of 200 °C, and some even contain higher flash points up to 280 °C. Therefore, the flash point of engine oil 15W40 has 215°C (419°F).

How to Determine Flash Point?

During determining the fuel properties, flashpoint plays a key role. Each engine oil contains a specific flash point, so you need a separate deterministic test to get each oil sample.

This test is crucial for customers to determine whether the oil suits their system. For example, if the oil flash point is 180°c, you can’t use this oil when the temperature reaches above 180°c.

According to Cleveland, oils with a flash point more significant than 79°C are defined by the ISO 2592 standard in an open crucible. In contrast, you can measure oils with a flash point below 79 °C in closed crucibles.

Flash Point Of Lubricating Oil

Flashpoint must evaluate the lubricant quality and determine its suitability for an application. This word describes the lowest temperature where vapors releasing by lubricant combustion.

Thus, low-flash points lubricants will burn earlier than high-flash points lubricants. When choosing lubricants for use in the gas and oil sector, this is the first property that you should consider. In addition to evaluating a lubricant’s fire hazard and safety credentials, flash points can provide insight into other properties.

When mixed with viscosity and specific seriousness tests, flash points can help establish crude oil quality. Mainly, no one ignored that flash points are essential when choosing lubricants. ASTM D93-20 is another famous strategy used to determine the flash point in the temperature range of 40 °C to 370°C.

Flash Point And Fire Point Of Lubricating In Experiment:

You should test lubricating oil for critical systems like propulsion plants, auxiliary engines, and steering gear per company specifications. This can vary for onboard lubricating oil experimenting every 15 days or once a month.

Taking Samples for Testing

Onboard lube oil is tested by sampling from the sampling point, which should be after the system. Before taking a sample, you should drain the oil to remove oil that has settled at the sampling point.

It would help if you kept the sample in the control room for cooling to average atmospheric temperature. While doing this, the lid of the sample bottle must be half open. Otherwise, the vapor will condense back into the sample during the cooling process.

Onboard Lube Oil Tests

To test all types of lube oil, you should do the following:

  • Water Content Test

A 5 ml sample is mixed with 15 ml of reagent containing paraffin inside the digital water content meter. Before closing the digital meter, a sealed bag containing calcium hydride is placed. The meter is shaken by hand. The chemical reaction in the test vessel is shown on the digital display as a water percentage.


  • pH Test

Adequately, using pH paper, this test will change the color once after oil exposure. Then it’s compared with a standard value. This experiment determines the oil samples reserve alkaline.

  • Viscosity Test

This test is done using a flow stick which provides two ways for oil to flow side by side. One path is filled with fresh oil, and the other is filled with used sample oil. The flow stick will title, and oil will flow in both directions due to gravity.

A finishing point will give with reference points along the flow stick. The used oil position will be checked when fresh oil reaches the finish point. This procedure shows the lubricating oil pollution due to heavy oil, sludge, or diesel oil.

  • Spot Test

In this test, a drop of lubricating oil is put on blotter paper and allowed to dry for several hours. Then, the dry spot is compared to an available standard spot to determine the insoluble ingredients of lube.

  • Flash Point Test

Using the Pensky Martin Closed Cup apparatus you can do this test. It determines the temperature at which the vapor will ignite when provided with an external combustible source. According to the regulations, this device was usually operated on passenger ships.

  • Water Crackle Test

Adequately, this is another technique for determining the presence of water in lube oil. In this way, the sample of oil drops will heat over a flame in an aluminum container.

Mainly, if there is water, a crackling sound will occur. Regular flash point and fire point monitoring will ensure that your motors run in peak condition.

Flash Point Of Motor Oil

Synthetic Motor Oil Flash Point:

Synthetic motor oil is manufactured to resist the temperature. Fully synthetic motor oils are less prone to combustion than traditional motor oils and semi-synthetic. Remember, if synthetic oils reach too high temperatures, this oil will be combustion.

Most synthetic motor oils have a flashpoint of 450°F; on the contrary, premium synthetic motor oils have a flashpoint of up to 700 degrees F or 371 degrees C!

Diesel Oil Flash Point:

The lowest temperature is the flashpoint of any fluid. It will form adequate vapor to create an explosive mixture in the air. In low flashpoint temperatures, it’s easy to combust the air if an ignition source is present. Usually, in higher flashpoints, you can safely handle it.

Diesel oil flash point is dependent on the type of fuel. Accordingly, the diesel oil flash point is 125 and 280° F and 52 t0 82° C. The flashpoint of any fluid will change when the air pressure around it changes.

FAQ (Frequently Asked Questions):

Q. How to increase the flash point of oil?

Adding water and some solid substance can increase the oil’s flash point. When it heats, It may help to falsify the EP figure a few times. In this case, the decomposition temperature will be too high.

Q. Is a higher flash point better in engine oil?

Yes, if the flash point is higher, it’s better. 400° F is the minimum ideal to prevent high costs. Even the best petroleum oil flashpoints will be between 390 and 440° Fahrenheit.

Q. What are the flash point and fire point of motor oil?

Usually, the motor oil flash point is the lowest temperature where a volatile combustible substance vapor can ignite in the air. Therefore, to sustain combustion, steam may need to make faster at the flash point. That’s why the fire does not last in most cases.

Flashpoint is necessary to measure how flammable a fluid is and its hazard level. The motor oil fire point is the temperature at which it can burn for at least 5 seconds after ignition.


The fire point is a slightly higher temperature where steam burns after ignition. None of these parameters are related to the ignition source or boiling liquid temperatures, which are very high. When choosing fire-resistant grease, it’s not essential to consider fire points.

Q. What Is the flash point of heating oil?

Typically, to heat the central heating system, heating oil is necessary. You can find two types of heating oil such as kerosene and had oil. The flash point of heating oil is 52–96 °C or 126–205 °F.

Final Word:

Finally, to determine the fuel economy, the flashpoint is an essential factor. The fuel consumption for a low flash point can be higher, and fuel economy will be down.

Various factors, such as oil cracking and pollution with gamma rays, cause a drop in the oil’s flashpoint. Ultimately, you can test a flash point of motor oil in an open crucible.

On the other hand, this is the article where we discuss several oil flash points. After reading this article you get the valuable information that you want.





I am Engr. Z Eusuf Lubricant Specialist, Mechanical Engineer & has been working with engine lubricants for a long time and knows what makes them work best. I can help you find the right oil for your needs, and I have tips on how to keep your engine running at its best.