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Engine Oil Viscosity Rating: What It Is & Why It’s Important

Engine oil is the heart and soul of your car’s engine. Vehicles would not function without it. Engine oil serves as a lubricant that prevents all the car’s critical parts from breaking down. It keeps metal parts from rubbing against each other during the combustion process, which helps your car get you around town as smoothly as possible.

Using the correct engine oil can make all the difference in your engine’s functionality and your vehicle’s lifespan. There are various levels of engine oil viscosity, such as 5W-40 and 10W-30, which can make it difficult to know which one is most satisfactory for your vehicle.

Understanding engine oil viscosity will assist you in understanding the importance of engine oil and which type you should be using in your own vehicle.

What Do The Numbers Mean?

Not sure what all the numbers on the oil cans mean? It’s actually quite simple: the numbers represent the viscosity of the oil. Viscosity represents the measure of a liquid’s resistance to flow. Low viscosity oil flows easier and is thinner than high viscosity oil; therefore, the higher the number on the bottle, the thicker the oil.

A practical way to grasp the difference between low viscosity and high viscosity oil is comparing water and honey. Water is thin, light, and flows much easier than thick, rich honey because it has a significantly lower viscosity than honey.

Temperature & Engine Oil

Engine oil acts differently based on the temperature outside. Oil flows much easier during the summer while it thickens during the winter. Living in either extremely hot or extremely cold climates will affect which
type of oil is best for your engine.

This idea is reflected in an oil’s viscosity description. The first number represents the thickness of the oil at low temperatures, or “winter” temperatures (hence the “W” in the oil’s name). The second number represents the thickness at typical operating temperature. For example, a 5W-30 oil means that the oil has a viscosity of 5 in lower temperatures and 30 in higher temperatures. If you’re living in the Phoenix area, it’s critical to ensure your engine oil can sustain high temperatures.

When operating your vehicle in a hot Arizona summer, you would think it would be better off using something like a 20W-50 oil compared to a 5W-20. The intense heat will thin out your oil more than the average climate, making it easier for oil to leak through faulty oil pan gaskets, causing damage to your engine.

However, it is recommended to always follow the recommended viscosity from the manufacturer. Modern vehicles are designed to use a thinner oil in both winter and summer. Engines are very sophisticated, using cam phasers and variable
valve timing, which change the engine timing for power and economy according to how you drive. These phasers require lightweight oils to pass through the tiny orifices when the oil is cold to work properly. If the oil isn’t thin enough
the engine can suffer a catastrophic failure.

One of the most common oil viscosities is 0w-20, which is thin enough for the winter and thick enough for the summer. You might think 0w-20 is not thick enough for the summer heat, but the engines of today are designed to perform with lightweight oils.

Engine Oil Viscosity Chart

The best place to find which oil viscosity your car requires is in your vehicle owner’s manual. However, an oil viscosity chart is an easy way to know whether or not your oil supports the climate you live in, which can be useful for living in a unique climate such as Arizona. The chart is a nice reference for being positive that your oil is not damaging your vehicle.

blue and red bar chart showing recommended viscosity at different temperatures
Image courtesy of

What Happens To Your Engine If It Has The Wrong Oil Viscosity?

If the cold winter months thicken your oil and hot summer months thin it out, how exactly does that affect the functionality of your engine? Using oil that is either too high or too low in viscosity can cause substantial damage to your engine and reduces your fuel economy. If oil is too low in viscosity during the hot months, your car may have a hard time staying lubricated. If oil is too thick during winter months, your car will have trouble lubricating and starting, and its fuel economy will worsen.

Wrong Oil Symptoms

Your Car Is Hard To Start Or Makes Clicking Sounds In The Cold

If engine oil is too thick, it will not lubricate all parts properly, causing extra resistance while the car tries to start. Since cold weather naturally thickens the oil, this is more likely to happen during winter months. If this happens, there is a decent chance that you need to switch to a lower viscosity oil.

Oil Leaks

Using synthetic oil on an older vehicle may cause oil leaks. Synthetic oil has smaller molecules than conventional oil, and it can move through tighter areas more easily. If you notice oil leaks, consider switching to a conventional oil with the same viscosity.

Burning Oil Smell

While higher viscosity oil causes issues in frigid weather, lower viscosity oil can cause issues in warmer weather. The hot weather can prevent the oil from properly lubricating the engine, which in turn causes the oil to burn. Excess friction between the metal parts of your car can cause long-term damage.

Engine Noises

A ticking noise coming from your engine can indicate that the engine is not properly lubricated. Those noises represent pieces of metal rubbing against each other, which could cause long-term damage to your engine. Anytime you hear squealing, ticking, grinding, or any other abnormal noise, changing your oil could combat the problem.

Poor Fuel Economy

If you find yourself making more trips to the gas station than usual, there’s a chance that your oil is too thick for your engine. Higher viscosity oil increases friction between important metal parts, forcing the engine to burn more energy than it needs to.

Finding An Affordable Oil Change

You’ll be impressed by the ease of scheduling an appointment online, and once you arrive for your oil change service, it will include lube, oil, and filter along with a check and top off of fluids, multi-point inspection, tire pressure check, and
rotation in about an hour.

Sun Devil Auto carries superior-quality oils and hires experienced ASE-certified technicians to perform maintenance and repair services at a price that is often less than the dealer. Value, superior service, and friendly staff with a location in your neighborhood? That’s Sun Devil Auto!