Engine oil is both – the life and the lifesaver for any engine. You would notice that a modern vehicle requires engine oil to function well and last long. Also known as motor oil, engine oil is an indispensable element for any vehicle’s engine. The engine oil comes in varying types; mineral oil, synthetic oil, or semi-synthetic engine oil. They all have some important functions to perform in the engine. These functions are:

  • Cooling
  • Cleaning
  • Lubricating
  • Protecting

Since oils are non-conductive or least conductive, they can perform the above-mentioned engine functions properly. However, do you want to know how exactly does the oil do all this? Click here!!

Read on to understand engine oils and their conductivity in detail. First, let us see what engine oils are made of.

The Composition of Engine Oil

Motor oil consists of base oils and other compounds. These compounds are hydrocarbons. A perfect combination of base oil, additives, and preservatives creates an excellent quality engine oil that works just fine for modern vehicle engines today.

The basic elements present in an engine lubricant are as follows:

  • base oil,
  • detergents,
  • dispersants,
  • viscosity improvement additive,
  • protection,
  • traces of other compounds.

The picture above displays a regular engine oil’s detailed composition, however, the more specialized and performance-driven an engine is, the more this assembly will vary!

Based on the way they are processed and manufactured, we can divide engine oil into three categories.

  1. Mineral oil
  2. Synthetic oil
  3. Semi-synthetic oil

All these three motor oils have different composition and processing. Let us look at each one of them.

The picture shows the quality difference between Mineral oil and Synthetic oils

Mineral oil

Mineral engine oil is produced from crude petroleum. After extraction, the crude petroleum goes to the refinery, where it undergoes many refining processes. This helps in clearing as many contaminants as possible. This oil largely consists of oxygenated or non-oxygenated hydrocarbons, and it also has sulfur or nitrogen traces. A hydrocarbon is an organic chemical compound composed only of hydrogen and carbon atoms. After processing, preservatives are added for performance improvement.

Synthetic oil

As the name suggests, this is chemically produced oil, which is made inside the laboratory. The production and processing of synthetic oil is more complicated than that of mineral oil. This is because of structural modifications, which is made to the hydrocarbon molecules involved in this process. The modification methods specialize in extracting the best molecules for oil production. Just like mineral oil, many additives get mixed in this composition to create superior quality synthetic engine oil. For this reason, synthetic engine oil is well known for its fine quality and is the most expensive out of the three types of oils. However, vehicle lovers will spare no expense, and so, this remains the most preferred too.

Semi-synthetic Oil

Semi-synthetic oil is an amalgamation of mineral oil and synthetic oil in varied proportions. This oil also has many additives and performs better compared to mineral oil. Moreover, semi-synthetic oil is cheaper compared to fully synthetic oil. This is because the production cost of this oil is lesser than purely synthetic oil.

If you want a detailed account of engine oil manufacturing, read on.

Now, let us look at the meaning of conductivity.

Conductivity is contrary to resistivity, and it shows the ability of any material to pass current (or allow electricity to flow through circuits) during an application of a potential difference. Some metals are good conductors to heat and electricity, while oils are not. As far as oils are concerned, most oils are poor conductors of heat and electricity.

What is Electrical Conductivity

Electrical Conductivity is the capacity of a solution to conduct electrical current. The ions (acids, salts, etc.) mixed in any solution are the ones that carry electrical current. Ions with lost electrons get charged positively and ions with gained electrons get charged negatively. The higher the number of ions in a solution, the higher will be the number of electrons being transferred, making the solution more conductive. Conductivity is used to measure the volume of dissolved solids in a solution.

What is Thermal Conductivity

Thermal conduction is the diffusion of heat within one or more materials that comes in contact with each other. The object with a higher temperature has molecules with more kinetic energy. The thermal conductivity of liquids like oil is generally far lower than that of solids. In liquids, the thermal conduction is caused by atomic or molecular diffusion.

What Makes Oil a Poor Conductor of Electricity

Is engine oil conductive? One could say, Yes! But, only to a very small perceivable amount.

For any liquid to conduct electricity, as discussed above the presence of electrolytes is a must. These electrolytes are charged ions that are not present in engine oil. The most common example of a liquid that conducts electricity is saltwater. The following two reason will explain why is saline water conductive.

The simple illustration shows electric conductivity in salt water.

When Sodium Chloride(NaCl) commonly known as table salt gets mixed into water, this mixture produces Na+ and Cl- ions. These ions have the capacity of carrying a charge. Furthermore, water has other similar ions of Sulphate and Potassium to make charged particles. Such ionic substances get mixed in water and can carry a charge.

When we look at this reaction-

H2O -> H+ + OH–,

Water also ionizes itself and produces electrolytes. At 25o Celsius, the accumulation of each of the above ions is 1×10-7 molL-1.

On the other hand, oil is completely different. Oil does nothing that a mixture like saltwater does. The composition of motor oil is a combination of long, non-polar hydrocarbon chains. By nature, engine oil cannot ionize in order to produce ions that can carry an electric charge. In addition to this, as oil is non-polar, ionic substances like common salt cannot be mixed into oil. Hence, oil does not conduct electricity.

What Makes Engine Oil a Poor Conductor of Heat

As we know, engine oil is a liquid. Liquids have loosely packed molecules. When heat travels in any source by the method of conduction, the bonds between the molecules need to be strong. This helps the heat to travel right till the end and make it across the medium, down the line. With liquids like engine oil, this travelling isn’t smooth. Oil cannot support this process because the intermolecular forces are weak.

Thermal conductivity in engine oil is not nil. It is present, but, it is negligible. If you look at the picture below, you see the arms are connected, but, the range is quite short. Hence, the oil will conduct heat up to a short distance, but the entire volume will not conduct heat effectively. This is why, oil is a poor thermal conductor.

Exceptions

So far, we have seen that engine oils are poor conductors of heat and electricity and are only slightly conductive. As a result, they are good insulators. However, depending upon their composition, oils can also conduct electric current. The conductivity may depend on numerous factors like:

  • Base oil,
  • Additives, and
  • Polarity.

High polarity makes a lubricant lesser refined and more conductive. According to the American Petroleum Institute (API), base oils and additive can be divided into 5 groups. This shows how additives change the role and conductivity of oils.

Group I:

These are the cheapest base oils in the petroleum market because Group I base oils are solvent-refined, which is a very simple and cheap refining process. The API classifies this group of oils as less than 90% saturates, and they have over 0.03% sulfur. They have a viscosity-index range of 80 to 120 and their temperature ranges from 32 to 150o F. These oils have fairly low conductivity.

Group II

Mostly used as simple engine oils, Group 2 oils are manufactured with the help of a complex process of hydrocracking. This manufacturing method is more advanced than the Group 1 refining process. The oils in this group have over 90 percent saturates and lesser than 0.03 percent sulfur. Group 2 oils have a viscosity index of 80 to 120. The hydrocarbon molecules of these oils are saturated, they possess anti-oxidation properties, and they cost more than Group 1 oils. Their appearance is quite clear. These oils are used as simple engine oils that is why they have very poor conductivity.

Group III

Manufactured under high pressure and heat, these aggressively hydrocracked oils are refined even more than Group II base oils. Used high-end engine oils and lubricants, these oils are processed for a longer duration extensively to deliver a purer base oil.

They are made with crude oil, but they also fall under the category of synthesized hydrocarbons. Equipped with super low conductivity group 3 oils are popular.

Group IV

These are the synthetic oils that we discussed above in types of oils. The name of these oils is Polyalphaolefins (PAOs). The sophisticated process of synthesizing is used to manufacture Group 4 oils. These have a very wide temperature range and are very well accepted as expensive engine oils in colder countries. It is poor conductivity makes it an excellent industrial lubricant as well.

Group V

These oils fall into the category of other oils which might include oils like silicone, phosphate ester, Polyalkylene glycol (PAG), polyol ester, bio lubes, etc. Group 5 base oils can be mixed with other group oils to enhance the oil’s properties. For example, Esters are common Group V base oils added to lubricant formulations to improve the quality of the oil. These oils can perform well in higher temperatures and have a longer life, even if adverse engine environment. Since these oils go through extreme polarization, their conductivity score is quite high.

Refer to the table below to get a better look at the mentioned details of all 5 groups of engine oil.:

Does The Age and Usage of Engine Oil Make it More Conductive

Engine oil gets oxidized and contaminated after prolonged usage. The group division above shows that the purest base oils are less conductive. The used engine may contain particles of carbon and metal plus oil oxidation products. This makes used engine oil more conductive as compared to the new engine oil. Still, one must note that conductivity will not be quite high. Conductivity will increase with age, but the bounce value will be marginal.

Conclusion

Engine oil cannot carry electric charge because there are no charge carriers or ions present in it. Ionic substances like table salt can be mixed in water to be used as a conductor of electricity. However, salt is not soluble in engine oil. Hence, engine oil is non or marginally conductive. Heat transfer by conduction requires strong bonds between the molecules, but this is not the case with engine oil. This is how we can establish that engine oil is a poor conductor.

Engine oil is the saviour of your vehicle’s engine. The poor electrical and thermal conductivity is a boon for your engine. It’s not difficult understanding why because the engine oil has to perform many roles to enable an otherwise vulnerable engine. Here are some most important things engine oil does for your engine:

  • Lubricates the engine- The major role of engine oil is to grease the running components of a vehicle’s engine. This is required because an automobile engine needs protection against constant resistance. So, a good quality engine oil saves the engine from wearing out because of friction.
  • Acts as a Cooling agent- As engine oil is a poor thermal conductor, it is used for keeping the engine temperatures under control. The heat loss in the engine through combustion and continuous friction makes the engine boiling hot. The cooling effect provided by engine lubricant plays a vital role in keeping the engine from overheating and sustaining damages. Hence, this cool property of non-conductive engine oil partly does the work of an engine coolant too.
  • Keeps the engine clean- Yes! The otherwise dark and viscose looking engine oil has the power to keep your engine clean and healthy. Since the purer oils are almost non-conductive, they help in keeping the engine clean.

If we compare engine oil to other lubricants, we can easily understand that it is this non-conductive nature of engine oil that makes it an excellent lubricant. For example, soapy water, though is a stable lubricant, is also a decent conductor of electricity. Since there is way too much electricity involved with your vehicle, this is not a good idea to have a conductor, electric or heat, running around your wheels. Therefore, insulation makes engine oil a better choice for your car. If you would like to read more on engine oil, click here.