When and How to Change Engine Oil in Your Car

When you get into a new car or used car, one of the first things you likely will ask is how to maintain it or how well it has been maintained. In the case of a used car, knowing whether or not it’s been maintained, such as by seeing oil change records and other service information, could make or break the deal. When it comes to engine oil, why does it need to be changed? How often does the average car need an engine oil change? Can you change engine oil yourself?

What Does Engine Oil Do, Exactly?

Engine oil serves several important functions in the engine. Primarily, engine oil lubricates moving parts and operates hydraulic actuators. During its journey through the engine, removing heat from the engine, its secondary function, tends to shorten its lifespan. As we know, engine oil is a petroleum product, just a few steps down from gasoline and diesel fuel in the refinery tower. Even some synthetic oils use petroleum bases, and all synthetic oils are various grades of hydrocarbon. When faced with heat inside an engine, they all do the same thing: They burn.

Petroleum and synthetic base oils, anti-wear and corrosion inhibitors, dispersants, detergents, and anti-foam additives eventually succumb to the overwhelming heat in the engine. Over time, both the bases and additives in conventional and synthetic motor oil oxidize, vaporize, or degrade. While the oil filter can remove some of the leftover deposits, most of the leftover material flows straight through, which you’d notice as a marked darkening of the oil. Less-noticeably, the oil viscosity is changing, as is its ability to lubricate and cool the engine.

Dark oil is absolutely normal, and the engine is designed to handle this gradual change, but only to a certain point. Eventually, continuing oxidation and vaporization further degrades the oil, at which point it starts to leave deposits of itself in low-flow areas, such as in the valve covers. Oil and additive deposits and sludge reduce the amount of free-flowing oil in the system, leading to a vicious cycle of increased motor oil overheating, oxidation, vaporization, and deposits. Given enough time, the engine can convert the entire oil charge to useless sludge in less than 25,000 miles. With no oil to lubricate engine bearings, timing chains, and high-pressure fuel pumps, engine failure is just a few revolutions away.

How Often Should Motor Oil be Changed?

The whole point of regular maintenance is to replace motor oil before it starts to leave deposits of itself in the engine. The old rule of thumb used to be every 3,000 miles, but engine manufacturing and motor oil formulations have made significant advances, today’s automakers recommending oil changes every 5,000 or 7,500 miles, some up to 10,000 miles or more.

In general, you should stick to the automaker’s recommended oil change interval, and adjust your personal interval depending on a few factors, including how often you drive, how you drive, what kind of oil you use, and how old the engine is. Take, for example, a Toyota Corolla, California’s favorite vehicle, for which Toyota recommends a basic oil change interval of 10,000 miles or 12 months. Here are a few reasons you might opt to change motor oil every 5,000 miles or 6 months, instead:

• Insufficient Mileage – While the average American driver puts on about 11,500 miles per year, there are plenty of people who put far less mileage on their vehicles. In this case, motor oil should be changed every 6 months, even if it hasn’t reached the 5,000 or 10,000-mile interval.
• Stop-and-Go Traffic – It’s often been cited that stop-and-go traffic is an engine killer, and it can be, but only if there are other problems that lead to overheating. Cooling system problems, for example, would lead to overheating and potential engine damage. Engine oil, though, doesn’t suffer in this condition.
• Towing and Hauling – Added weight and drag, such as from trailers, gear in the junk, or rooftop cargo, increases stress on the engine and transmission, most notably in the generation of heat. Heat, of course, leads to oxidation, shortening motor oil lifespan. Get an oil change more often if you tow or haul regularly, or consider installing a secondary oil cooler.
• Many Short Trips – Water vapor (H ₂ O) is a major byproduct of combustion and oxidation, which can condense in the crankcase when the engine cools off. Warming the engine to operating temperature vaporizes the water, allowing it to escape, but short trips don’t give the engine time to heat up. Condensed water sits longer in the oil, increasing the production of performance-robbing acids and deposits. Change the oil more often or work in longer trips at least one a week.
• Excessive Idling – Similarly, engines that idle excessively, are putting on revolutions without adding miles, which makes oil change “mileage” intervals hard to count. Not that we’d use a Corolla as a police vehicle or ambulance, but maybe as a delivery vehicle or real estate runabout, a lot of engine wear could rack up without showing on the odometer.
• Oil Life Monitor – Some vehicles come with what is known as an oil life monitor (OLM), which can be a good guide to determining your next oil change interval, but is not the same as Toyota’s Maintenance Reminder, a purely mileage-based calculation. Algorithm-based OLMs base their oil change indications climate, trip duration, engine temperature, and other data, much like the previous list. Sensor-based OLMs take direct measurements of the oil, such as conductivity, viscosity, soot concentration, and water content, calculating how much life the oil has left before it should be replaced.

Changing Your Own Engine Oil

When it comes time for an oil change, you can go to a service center or your local shop, but you can also save a few bucks by doing it yourself . All you need is a couple of ramps, a couple of wrenches, an oil drain pan, and a funnel. Rags, safety glasses, and rubber or nitrile gloves are also good to have. Here is the basic guide:

1. Temperature is important, but not critical. If the engine is cold, idle 5 or 10 minutes to improve oil flow for draining. If the engine is hot off the highway, waiting 20 minutes will prevent possible burns.
2. Drive the vehicle up onto the ramps, set the parking brake, and shut off the engine. Open the oil fill cap and pull out the dipstick.
3. Place the drain pan to catch oil from the oil filter, and remove the oil filter. You might need an oil filter wrench for removal. Check that the gasket comes off with the old filter. Otherwise, you’ll have to pull the old gasket off the engine. Use a rag to clean the oil filter mount and surrounding areas.
4. Apply a thin film of new engine oil to the gasket of the new oil filter, then spin into place. Once the gasket makes contact, tighten the filter an additional 180° to 270° (1/2- to 3/4-turn). Do not use the oil filter wrench to tighten the oil filter.
5. Place the drain pan to catch the oil from the crankcase, and remove the oil drain plug. Be sure to remove the plug slowly, so you don’t lose it in the drain pan and to prevent undue splashing.
6. Once the old oil drain slows to a drip, replace the oil drain plug, tightening no more than 45° (1/4-turn). Clean up with a rag.
7. Place the funnel in the oil fill hole, and slowly add oil until you reach the capacity listed in your owner’s manual. Replace the oil fill cap and clean any spill immediately with rags.
8. Start the engine and look under the vehicle for any leaks. If all is well, roll the vehicle back down the ramp on a level surface. Let the engine run for 2 minutes, and shut it off.
9. After the engine has sat for 5 minutes, use the dipstick to check oil level, adding if necessary.

Changing engine oil is an important part of proper vehicle maintenance. At Auto City we do not just sell used cars, we service cars as well!  Our service department is ready for any job – big or small. Check out our oil change specials too!