Oil is one of the most important fluids involved with the inner workings of an internal combustion engine. But who actually knows what engine oil is, and what do the automotive engineers expect from it? To put it simply, engine oil is a derivative of crude oil. Crude oil is found in deep underground pockets, from where it’s extracted and undergoes several refining processes. Among the many carbon chained molecules found in crude oil, engine oil is differentiated as the long chain alkane, cyclo-alkane, and aromatic molecules. Once sorted in refinement, these molecules are blended with detergents and additives to give the base oils alkalinity, corrosion resistance, and viscosity.
Alkalinity refers to the oil’s ability to absorb and neutralize acids- the unit of measure for this in petroleum products is known as the Total Base Number (TBN). Corrosion is common in engines from colder climates, so it is important for these fluids to be manufactured to protect against it. Viscosity is the fluid’s measure of internal friction, so in layman’s terms– how fast a fluid will flow. Engines require their oil to be a certain viscosity at operating temperatures (230-250°F) but also during cold start temperatures (30-70°F). Viscosity improvers do just this by changing the natural viscosity of base oils to give them the ability to remain fluid through a specified range of temperatures. This is accomplished by the improvers shortening their molecular chain as temperatures drop and lengthening when temperatures increase, therefore keeping the oil from running too thick at cold morning starts and too thin at operating temperatures. All of these additives play a crucial role in domesticating the crude oil for use in engines- so much so that oil change intervals are calculated based on their life spans.
Of the many roles oil has in the engine, its most important is providing lubrication to all the moving metal parts. The bearings inside the engine are designed to have a film of oil in between the bearing wall and rotating shaft (as illustrated). A jet also continuously coats the cylinder walls with a layer of oil to lubricate the pistons as they blast up and down. Oil is additionally delivered to the top of the engine where the valves are operated by a spinning camshaft. Apart from lubricating, a side job that oil provides is cleaning the engine of impurities produced by it being operated at such high temperatures. Metal shavings and soot are picked up and carried off to the oil filter to get sifted out before the oil recirculates back through the engine. As mentioned above, an oil’s Total Base Number (TBN) reflects its ability to combat acid. Condensation that forms in the engine can react with Sulfur present in low grade gasoline and will produce sulphuric acid – fresh oil can neutralize this acid and also halt corrosion before either can reap damage to an engine’s internals. One of the last notable jobs of oil that we’ll touch on is it drastically reduces the amount of heat produced in the engine. But we’ll dive deeper with this in the next paragraph.
Considering all of the research and planning that goes into refining our oil, what happens if an engine is run without it? The short answer ultimately is catastrophic engine failure. Without oil lubricating the bearings, the metal to metal contact will produce friction. The friction then results in an abundance of heat with no where to go. Running the engine in this condition will eventually cause the shaft to bond to the bearing, resulting in a spun bearing. Similarly without oil, the piston rings will rub against the cylinder walls, scoring the walls and again creating a considerable amount of heat. If the engine continues to be run without oil, damage will continue to build and the engine will eventually seize-up. There is a hazard light built into your dash to alert the driver if the engine has no oil pressure. Lack of oil pressure can result from an oil pump failing, a pump’s intake becoming clogged, or a car that simply has no oil. We recently had a vehicle towed to our shop with a failed oil pump that was essentially starving the engine of oil. The driver fortunately noticed the oil light had illuminated and turned the car off immediately. In this instance, the oil pump had spun itself on the crank and the grooves inside were shaved down so that the pump was no longer spinning. Below on the right you can see where the inside grooves should be on the new pump; on the left is the pump being replaced where they’ve been rounded off.
Lastly, one misapprehension that has become recently popular is that newer car technologies allow for longer maintenance intervals. A lot of automotive marketing campaigns have seen recent success in advertising their vehicles as low maintenance, and consequently recommending less frequent oil changes. This is inherently misleading and will produce a lot of long term problems for consumers, but for all intensive purposes we will focus our scope of this topic to the oil ramifications. The tolerance of oil breakdown is dependent of the oil, not the modern designs to an engine. The result of an extended service interval is oil breaking down and turning into thick sludge that cakes all over the engine. The danger of this could be compared to plaque building up in a person’s arteries – it goes unnoticed until one day it begins restricting the flow of the blood. Just like plaque, this sludge can build up overtime to the point of thin oil passages becoming blocked and oil no longer reaching where it’s needed. No matter the cause, whether a faulty oil pump, no oil at all, or a build-up of sludge, any engine that is starved of adequate oil will fail prematurely.
So all of this being said, what are the best practices with oil to protect your engine? The most obvious and repeated direction in this post would be to change your oil every 3,000 to 5,000 miles. This ensures your engine will always have fresh oil, functioning viscosity improvers, strong protection against acids, proactive protection against sludge build up, and a new oil filter. With age, most cars will eventually leak or burn oil so it can also be worth the two minutes to stop and check your oil level when fueling up or before a long trip. Periodically checking fluid level is an easy way to protect your investment because it allows you to monitor the level and gives you the flexibility to alert your mechanic of a leak before it becomes major. Lastly, if your oil light has illuminated while the engine is running, shut your car off as soon as it is safely possible to do so. We mentioned above a red oil light indicates there is no oil pressure, so continuing to drive your vehicle can result in irreparable damage to the engine.