The Ultimate Guide To Engine Oil (Explained for Beginners)

Ultimate Guide to Engine Oil

Oil is your car’s best friend. It flows through your engine, protecting vital components, and ensuring top performance.

However, not all motor oil is the same. You can’t just grab any ol’ bottle of oil off the shelf. Instead, how you drive, where you drive, and many other factors determine the type of motor oil needed.

Whether you’re an experienced DIY mechanic or a novice, you probably have some questions about motor oil. Well, we’ve got the answers right here in our Ultimate Guide to Engine Oil! It has everything you need to know about selecting and using the best engine oil for your vehicle.

Benefits of Engine Oil

You’ve probably heard oil referred to as the “lifeblood” of your engine. It’s an apt metaphor considering how many different things oil does.

Oil provides vital lubrication for the entire engine. It performs the following functions:

  • Prevents friction
  • Reduces heat buildup
  • Contains chemical buildup
  • Minimizes engine corrosion (oxidation)
  • Keeps engine clean

Here’s a closer look:

Preventing Friction

Engine oil prevents friction between components. After all, your engine consists of thousands of moving parts – most of them are made from metal.

Metal parts can’t grind against each other. Not only will engine performance suffer but damage, including catastrophic damage, will almost certainly occur. Oil allows metal parts to touch without grinding, which, in turn, reduces friction.

Helps Control Heat

Heat is friction’s natural by-product. Even a properly working engine creates substantial heat during operation. As long as the heat stays properly contained and managed, your vehicle works without issue. However, if too much heat builds up, problems soon follow.

Engines create a constant series of small explosions in a process called combustion. Without oil, the combustion process creates too much heat, which can overload the engine. The oil acts as an insulator to help keep the heat within safe levels.

Helps Contain Combustion By-Products

Combustion creates a chemical reaction which powers the engine but also leaves behind chemical by-products. The oil prevents potentially harmful by-products from entering other parts of the engine.

Oil’s slickness naturally attracts acids, silicon oxide, and other chemicals. It then suspends the chemicals, so they’re unable to damage the car.

Minimizes Oxidation

Commonly known as rust, oxidation is a persistent threat to most engine components. Preventing oxygen from entering the engine is impossible. However, motor oil helps prevent oxygen’s corrosive effects. A persistent lack of oil results in rust formation and eventual engine failure.

Cleans the Engine

Engine combustion creates by-products when running. These contaminants build up over time, clogging the engine with sludge and other deposits.

High-quality motor oil helps remove deposits. A clean engine disperses heat and operates at the highest level of efficiency.

Oil Components and Additives

Motor oil has two components:

  • Base oils
  • Additives

Base oils make up anywhere from 70 to 90 percent of the engine oil. The rest consists of additives. Note that the additives included inside the oil are different than Motor Oil Additives, which are separate substances you mix into the oil yourself.

Different types of motor oil contain different additives. Each one performs a unique function. Here’s a breakdown of the common additives found in motor oil:


Detergents remove sludge and debris while also preventing new deposits from forming. Clean engines operate at maximum efficiency. Keep in mind cleaning properties might not last for the duration of the oil. Stick to the manufacturer’s recommendations for oil changes to keep your engine clean.


Dispersants also help keep the engine clean. They allow the oil to hold contaminants, preventing buildup and deposits. The oil holds the debris until removal during an oil change.

Friction Modifiers

Friction modifiers help the oil prevent metal-on-metal grinding. Reducing friction extends engine life, prevents damage, and improves fuel economy. Friction modifiers usually lose their effectiveness before the oil needs changing, meaning they work best immediately after an oil change.

Anti-Wear Additives

Many oils add zinc to help create a protective layer for engine components. Specifically, zinc helps maintain high-pressure points near the camshaft lobes, lifters, piston rings, and cylinder walls. The coating created is often referred to as a “sacrificial layer.”


Oxidation lowers fuel economy and slows engine performance. It results from the exposure of oxygen at high temperatures. Over time, oxidation destroys metal components. Antioxidants help keep the engine clean by preventing grime buildup.

Anti-Foam Additives

Foam can cause a variety of problems. Tiny air bubbles in the oil reduce its ability to lubricate and cool. Plus, foam makes the oil move slowly through the engine, especially at high speeds. Anti-foam additives reduce foam formation.

Viscosity Index Improvers

The viscosity index measures oil’s ability to resist changes in viscosity. Adding polymers helps the oil maintain viscosity across both high and low temperatures. You’ll find viscosity index improvers in most types of multi-grade oil.

Rust and Corrosion Inhibitors

Water and heat form rust. Unfortunately, engines you’ll find plenty of water and heat inside an engine. However, rust and corrosion inhibitors help keep your engine rust-free. They coat metal components to protect against damage from water and acid.

Pour-Point Depressants

You’ll find pour-point depressants in many types of cold weather motor oil. They help the oil move through the engine even in subzero temperatures. Pour-point depressants help reduce stress on engines which spend lots of time in cold climates.

Viscosity Explained

All types of motor oil have SAE ratings. Created by the Society of Automotive Engineers, the SAE rating refers to the following two qualities found in the motor oil:

  • Function
  • Viscosity

Viscosity is a fluid’s ability to resist deformation caused by stress. In other words, it describes how well oil flows. Oil with high viscosity is thick; oil with low viscosity is thin.

Oil viscosity changes with temperature. It thins in hot temps and thickens in colder ones. Generally, high viscosity seals more thoroughly and provides superior lubrication compared to thin oil.

The SAE consists of two digits, a letter and two more digits. Examples include 10W-40, 10W-30, etc.

The first two numbers refer to the viscosity when the oil is cold. Testing occurs at zero degrees Fahrenheit. The lower the number, the less the oil thickens in the cold. For example, oil with an SAE rating of 5W-30 doesn’t thicken as much as oil with a rating of 10W-30.

Thick oil seals components and provides reliable lubrication. However, if the oil is too thick, it’ll reduce the vehicle’s fuel economy. Thick oil makes the engine work harder than necessary because excess oil covers the parts. Additionally, the engine will likely struggle to start.

A letter follows the first two numbers. Usually, it’s a “W.” While many people think the “W” stands for “weight,” it actually means “winter.”

The final two numbers represent the oil’s resistance to thinning. Measurements occur at 212 degrees Fahrenheit. The lower the number, the quicker the oil thins out. For example, oil with an SAE 10W-30 thins faster at 212 degrees than oil with an SAE of 10W-40.

Thin weight oil flows through all the moving parts of your engine, allowing it to operate at maximum efficiency. It provides the most lubrication.

Finally, you can also find monograde oils. They’ll have SAE ratings of 30, 40, or 50. Monograde oils aren’t used often today. They’re mainly for small engines such as those found in lawnmowers, generators, and gas-powered tools.

What Type of Oil Should You Use?

Always follow the manufacturer’s recommendation. It’s in your owner’s manual. Additionally, the oil type is often printed directly on the oil cap.

Your vehicle is specifically designed to work with a certain type of oil. Most modern vehicles use either 5W-20 or 5W-30. However, never guess about the type of oil required. Using the wrong weight will negatively affect your engine performance.

Additionally, you need to choose an oil with a viscosity appropriate for the climate. Cold environments typically require oil with low viscosity. Look for oil with an SAE rating of 0W-20 or 5W-30. Low-viscosity oil has the following benefits:

  • Protects components from freezing
  • Helps the engine start

Hot climates require viscous oil. Look for oil with an SAE rating of 15W-40 or 20W-50. Aside from use in hot climates, oil with a high viscosity is often commonly used in older engines found in classic cars.

Types of Motor Oil

Not all engine oil is the same. Three types are available:

  • Fully Synthetic
  • Synthetic Blend
  • Conventional or Traditional

Synthetic Motor Oil

Synthetic oil is usually the best option for most types of modern vehicles. Free from impurities, it’s a lab-created oil made under carefully controlled conditions. Most manufacturers recommend synthetic engine oil.


Synthetic oil is specifically designed for the needs of modern vehicles. It has the following benefits:

  • Improves fuel efficiency and gas mileage
  • Helps optimize engine performance
  • Protects against mineral deposits and buildup

Synthetic engine oil is also the best (and sometimes only) choice for cold weather driving. It circulates quickly through the engine upon startup, ensuring reliable starting even in cold temperatures.

Oil Changes

Synthetic oil doesn’t need changing as frequently as the traditional type. Most cars with synthetic oil only need an oil change every 10,000 miles.


Price is the biggest drawback. Synthetic oil is the most expensive type. However, comparing the price per bottle of synthetic versus traditional doesn’t tell the whole story. You don’t have to buy as much synthetic oil each year because you need fewer oil changes.

How to Find Synthetic Oil

Most synthetic oil is labeled synthetic, so finding it shouldn’t be a problem. Additionally, all oil with an SAE rating of 0W-30, 0W40, or 5W-40 is synthetic.

Common types of synthetic oil include:

  • 0W-30 Improved fuel economy
  • 0W-40 Increased engine performance and power
  • 5W-40 Protects against wear and buildup; helps cold startup

Check out the Best Synthetic Oil and read our reviews.

Synthetic Blend

Also called semi-synthetic motor oil, synthetic blend combines conventional and synthetic oil. Although it doesn’t deliver all the benefits of synthetic oil, it’s much cheaper. Plus, it’s superior to traditional oil.

Semi-synthetic oils reduce about three times the engine wear compared to traditional oil. However, you’ll have to change it more frequently than synthetic (but less than traditional).

Common semi-synthetics include:

  • 5W-30 Protects against debris buildup
  • 10W-40 Additional buildup protections
  • 15W-40 Reduces up to three times as much engine wear as conventional

Conventional Oil

Also called traditional oil, conventional oil is the original type of oil. It was used to lubricate the first engines, including the Model T.

Conventional oil derives from fossil fuels. While the refinement process is more sophisticated now than the Model T, the oil is the same as always. Modern conventional oils combine hydrocarbons, poly internal olefins, and other chemicals.

Conventional oil is the most affordable type. It’s often significantly cheaper than both synthetic and synthetic blend oil.

However, it also has plenty of drawbacks. Because it’s derived from fossil fuels, conventional oil will always have some level of impurities. Impurities can lead to engine knocking, debris buildup, decreased performance, and other issues.

Additionally, conventional oil requires frequent oil changes, usually every 3,000 miles or so. It’s also a poor choice for cold weather driving.

What Types of Vehicles Should Use Conventional Oil?

Many new cars use conventional oil but only during the initial break-in period. The process is often called “seasoning” the car.

Vehicles with simple engine designs can also use conventional oil. However, it’s not the best option for heavy-duty, aggressive driving.

Common Types of Conventional Oil:

  • 10W-40 Basic protection for simple engines
  • 15W-40 More protection but requires frequent changes

Potential Problems Related to Engine Oil

Motor oil doesn’t require tons of attention, but a few potential problems can occur. Unfortunately, because motor oil interacts with so many different aspects of the engine, any issues can seriously impair your car’s performance. Here’s a closer look at common oil-related engine issues:

Oil Pump Failure

The oil pump circulates oil through your engine. If it fails, an issue called “oil starvation” can occur. Oil starvation results in engine shutdown.

Oil pump failure is commonly caused by using oil with the wrong viscosity for the vehicle and weather. Make sure the motor oil is thin enough to flow through the engine.

Dirty Oil

You can tell a lot about your oil based on its appearance. Clean oil has an amber color. It’s clear. You should be able to see the dipstick through the oil.

Oil darkens and dirties over time. It’ll obscure the dipstick. Dirty oil should be changed right away. It clogs up your engine with debris.

Oil Smell Inside the Car

If you smell oil when you’re sitting inside the car, look out! It’s a big-time warning sign of a potentially serious problem.

An oil smell inside the cabin indicates a leak. If you smell gas or exhaust, oil is likely burning in the exhaust area. Your vehicle is overheating and might even catch fire. Stop driving and check in with a professional mechanic right away.

Knocking and Noise

Increasing engine noise often indicates low oil levels. When components aren’t properly lubricated, you’ll hear knocking, rumbling, and more. A small rumble indicates oil levels are low but manageable. However, persistent knocking signals a dire need for more oil.

Exhaust Smoke

Not all smoke signals a problem. A translucent vapor emitting from your tailpipe, especially in cold weather, is common and harmless.

However, thick, dark smoke can indicate an oil leak. Check your vehicle’s oil levels. If they’re unexpectedly low, oil might be leaking into the exhaust system.

How to Change Your Oil

Changing your oil is one of the easiest types of car maintenance. You should have no problem doing it even if you’re not an experienced at-home mechanic.

Equipment Needed

The key to success is using the right tools. Here’s what you’ll need:

  • Oil – Use our guide to find the best choice for your vehicle and driving needs
  • Oil Filter – Consult your owner’s manual for the specific size and type
  • Oil Filter Wrench – It attaches to the end of a socket wrench
  • Socket Wrench Set – Any standard set will work
  • Oil Drain Pan – Check out our Oil Drain Pan Guide for more
  • Funnel – Make sure it fits underneath the car
  • Rags and Kitty Litter – They’re great for mopping up spills
  • Mechanic’s Creeper – Read our Mechanic’s Creeper Guide here

Changing the Oil

It should take about an hour or less. You might get dirty, so wear old clothes. Also, keep kids and pets inside.

First, drive your car around the block. Run it for about five to 10 minutes. Heating the oil thins it, which helps it drain faster.

Next, park your car on a flat surface. Use wheel ramps on the front tires. They elevate your car without requiring the hassle of using a jack. Just a slight lift is usually all you need. Place stop blocks behind the rear tires to prevent accidental rollback.

Now you’re ready to remove the oil filler cap. It’s the same place where you add oil. Consult your owner’s manual for the exact location. Most filler caps have an illustration of an oil lamp along with a recommended SAE rating for the vehicle.

Next, you’ll go underneath your car to remove the oil plug. It’s a large bolt at the bottom of the oil reservoir. You’ll unscrew it with the appropriate socket wrench. Don’t remove it completely right now; only loosen it.

Set up the oil drain pan. Place it directly underneath the oil plug. Stay out of the way. You don’t want any oil to splash on your skin (it’s hot!).

Unscrew the oil plug with your fingers. Try to avoid dropping it into the oil pan because finding it can be a messy situation. Let the oil drain into the pan. It should take about five minutes.

Next, remove your oil filter. Finding your oil filter isn’t always easy. The location varies based on the make and model of your vehicle. Consult your owner’s manual.

Most filters pull out easily by hand. However, make sure your oil pan is ready below. Removing the filter often releases a stream of captured oil. Aside from the filter, remove its rubber gasket ring, too.

Install the new filter. Smear a thin line of oil around the gasket ring of the new filter. Doing so helps create a tight seal.

Next, replace the oil plug. Thread it into the hole in the underside of the reservoir. You can now remove the drain pan from underneath your car.

Finally, you’re ready to add oil. Check the owner’s manual for the specific quantity needed. Generally, modern cars require about four to five quarts. Replace the filter cap and close the hood.

Start your car. Let it run for a few minutes. Running the car helps oil circulate through the engine. Check underneath the car for leaks.

How to Dispose of Used Motor Oil

Used motor oil is a major toxic pollutant. It requires careful disposal. Never put used motor oil in the following locations:

  • The ground
  • A storm drain
  • With your regular garbage
  • In the toilet, sink or other household plumbing

Many auto parts stores, gas stations, and car repair shops accept used oil for recycling. Sometimes they charge a small disposal fee.

However, most locations don’t accept oil mixed with other substances, like gasoline. Instead, you’ll need to take it to a toxic waste disposal center.

Final Thoughts

The right oil increases your vehicle’s performance and lifespan. Use the information above to find the best type based on your vehicle, driving habits, and driving environment. Engine oil is arguably the most important substance you put into your car.

Treat your car well by using quality motor oil, and it’ll perform at a top level in return.

Brett Gordon

The engine behind editing at DigMyRide and the brains behind its build. During the day, Brett is a thirty-something dude from SoCal climbing the corporate ladder, but by night, he spends his time contributing to the online world of automotive tech & trends.