What Does Engine Oil Do?
Engine oil performs several functions;
As you can see, oil does much more than just minimise friction of moving parts in your engine. Engine oil must also protect against wear, maintain engine cleanliness, help to control emissions, cool the engine, hold engine contaminants in suspension, and in the case of some diesel engines, even help the engine to start.
How Do Engines Use Oil?
Although it is the fuel system (mixing fuel and air to flow into the cylinders) that makes our engines work, the lubrication system of a combustion engine makes sure that every moving part gets oil so that it can work easily.
The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most vehicles, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.
Oil collects contaminants from the combusting air and fuel in the engine. Exhaust gases can blow past the rings, dumping combustion products into your oil. These contaminants include fuel, acids, soot, and water vapor. These materials react with the oil and the additives, causing sludge, varnish, oil thickening and acid formation.
Some engine oils are formulated with detergents, dispersants and antioxidants to resist the effects of these contaminants, but eventually they too will be depleted. Oil effectively breaks down as it ages and loses the ability to lubricate so old oil must be regularly drained from the engine and replaced with new oil.
In colder climates or during the winter, increased condensation can cause engines to burn oil at a faster rate. Consistently changing your oil will contribute to safer driving, longer vehicle life and better overall engine performance.
Choosing Engine Oil
Firstly, you need to understand the 2 kinds of oils (Conventional vs Synthetic), plus you need to understand the various terminology used to compare and rate oil, and then you’ll need to make up your own mind what’s best for your vehicle and your back pocket!
Conventional oil is based on Petroleum. Differences between conventional oils usually lies within the purification process of the base oil and the additives that are included to control it. While some manufacturers process their own base oil (Mobil, Shell, etc), others buy base oil from these companies and add their own additives. Like most things, there are fewer engine oil manufacturers than there are engine oil brands. Many brands, especially generics, buy their oil from common manufacturers.
Conventional oils are sufficient for most engines, but synthetics tend to be favoured by owners of turbocharged engines and other high-performance engines.
Synthetic oil is also put together the same way as conventional oil. It has a base and additives. The difference is that the base oil is synthesized so that the size of the molecules are ideal for a particular weight and are of consistent size. With a pure base, there are no waxes or impurities that contribute to build up of “varnish” and “coke” in your engine. A more sophisticated set of additives is added to this ideal base oil. These additives make for an extremely stable engine oil which can maintain its viscosity over a larger temperature range and keeps the base oil molecules from breaking down. The result is an oil that can flow at much lower temperatures, maintain proper viscosity at higher temperatures (thermal breakdown), and remain stable for a much longer period.
The only real downside to synthetic oils is the cost. It is typically two or three times the cost of conventional oil for a good synthetic. Another little-known side-effect is that if you switch to a synthetic oil on an old engine, you may suddenly find you have oil leaks! It’s not that synthetic oil causes leaks, rather, the detergents in the synthetic oils will “clean-up” the varnish and sludge left by conventional oils and may reveal worn seals.
So, synthetic oil does not breakdown as quickly as conventional oil, but it still acquires contaminants the same way, however it has additives to help battle this meaning you have a little more leeway with the timing of oil changes.
Synthetic Oil Blends
Blended oil is an alternative to buying pure synthetic. It combines some synthetic base oil with conventional base oil. Typically it does not include the synthetic oil’s advanced additives.
The small percentage of synthetic base oil in a blend versus its price does not make it worthwhile. If money is not an issue, then just go with full synthetics.
Additives in Oil
Use of additives is an approach to improve and maintain oil performance. Because high engine temperatures will combine with moisture, combustion by-products, rust, corrosion, engine wear particles and oxygen, sludge and varnish will be produced. The role of oil additives will not only assist in maintaining good lubrication, but also help minimize sludge and varnish, and any damage that would occur to your engine as a result.
There are hundreds of oil additives on the market. Some say that they will reduce your mileage, or reduce your wear, or reduce your oil consumption, and some even say that you can run your engine without any oil after treating your engine with their miracle cure additive.
Keep in mind that the base oil package in any oil can range from 70-95% of the mix, the rest comprised of additives. However, since some base oils will actually have natural characteristics which reduces the need for additional additives, comparing % of additives between different oils doesn’t mean anything.
The ingredients in an additive package differ in cost, but price is just one factor. Some work better in certain combinations of base oils, and some of the less-expensive base oils are a good choice for a blend because of the way they perform with popular additives. Bottom line: every motor oil has a recipe. Refiners come up with a list of objectives based on the needs of their customers (vehicle manufacturers) and formulate oil to meet those goals as best they can.
The purpose is to keep the surfaces of your engine parts clean by inhibiting the formation of high-temperature deposits, rust and corrosion.
These additives disperse solid particles, keeping them in solution, so they don’t come together to form sludge, varnish and acids. Some additives work both as detergents and dispersants.
There are times when the lubricating film breaks down, so the antiwear agents have to protect the metal surfaces. A zinc and phosphorus compound called ZDDP along with other phosphorus (and sulphur) compounds are commonly used.
These reduce engine friction and therefore can improve fuel economy. Graphite, molybdenum and other compounds are used.
Oil contains wax particles that can congeal and reduce flow, so these additives are used to prevent that occurring.
This prevents oxidation (thickening) of oil. Some of the additives that perform other functions also serve this purpose, such as the antiwear agents.
The crankshaft whipping through the oil in the pan causes foaming. Oil foam is not as effective a lubricant as a full-liquid stream, so the inhibitors are used to cause the foam bubbles to collapse.
Used to protect metal parts from acids and moisture.
Below is a list of terminology that you may come across in regards to engine oil.
Viscosity is a measure of the oil’s thickness/resistance to flow. There are 2 numbers in the viscosity rating – eg. 30W-50. The first number relates to viscosity at cold temperatures, and the higher the 2nd number, the more resistant it is to thinning. Within reason, thicker oil generally seals better and maintains a better film of lubrication between moving parts.
Generally, if viscosity is too low, oil can sheer and loose film strength at high temps. If too high, oil may not pump to the proper parts of the engine when temps are low and the film may tear at high rpm. So 10W-30 oil has less viscosity when cold and hot than does 20W-50. What’s really important is that you use the oil viscosity your car’s owner’s manual recommends.
Multiviscous oils are one of the great improvements in oils but choose wisely – these oils are more prone to viscosity and thermal breakdown due to the high polymer content. For an engine used fairly little, when oil changes are infrequent, multi-viscosity oils are important so that lubrication is adequate in either winter or summer. The rule of thumb when selecting a multiviscous oil to select one with the narrowest span of viscosity for the temperature you will use it in.
Resistance to thinning with increasing temperature is called viscosity index. This is a number that indicates the rate of change of viscosity for a given temperate range. Again, generally the higher the number the better.
This property of oil is a major contributor to the life of your bearings. And although a higher second number is good, the oil also has to be robust. For example, oil tends to lose viscosity from shear, the sliding motion between close-fitted metal surfaces of moving parts such as bearings. So resistance to viscosity loss (shear stability) is necessary to enable the oil to maintain the lubricating film between those parts.
This is the temperature at which an oil gives off vapours that can be ignited. Flash point can be an indicator of the quality of base stock used. The higher the flash point the better (this property affects volume of oil consumed by the engine).
The base oil is that which is used in the formula before additives are introduced to make up the entire oil formula. Both synthetic oils and petroleum oils can be made from paraffin base oils.
Paraffin is recognized as the best lubricating oils and offer a number of advantages over napthenic oils. High quality 100% paraffinic oils are the best type of base oils. Both paraffin and napthenic are types of petroleum oils.
More of a winter issue for climates where freezing is likely. Basically, this is a number indicating a temperature level when the oil is too thick to move. The lower the pour point the better.
% Sulfated Ash
This is a measure of how much solid material is left when the oil burns. Low ash seems to promote longer valve life.
Other Vehicle Lubricants
Any moving part in a car can be optimized from a friction point of view, be it axles, brakes, steering system, gears, electric systems, locks, seats, safety belts, seals, etc. Many 4WD gearboxes, transfer boxes and differentials require a special grade of oil. As with engine oils, all lubricants will break down over time and need replacement. The selection of lubricants for these parts of your vehicle should be as important as the selection of engine oil and should likewise be regularly checked and changed on a preventative maintenance schedule.
Oil and Lubes Summary
Using the right grade of motor oil is as important as changing it consistently. As we’ve discussed above knowing what grade of oil is right for your vehicle is crucial.
Step 1 – Consult your vehicle’s manual for the manufacturer’s recommended grade
Step 2 – Consider how you drive your vehicle and in what conditions. If you drive in extremely hot or cold temperatures, make frequent short trips, spend a lot of time in stop-and-go traffic, or use your vehicle to tow or haul loads, your engine may need an oil that offers extra protection.
Step 3 – Consider the age of your vehicle and the number of kilometres it’s travelled when selecting the oil type and grade. As a vehicle’s engine ages, seals begin to deteriorate, gaskets become brittle and oil consumption increases. Special motor oil formulations, have been introduced to defend against engine wear and harmful deposits in vehicles with excess km on the clock.
By choosing the right motor oil and changing it consistently, your engine’s hard-working parts will slide
What Does Engine Oil Do?