When Should I Change My Oil?
This is a very important question that is worth your consideration. It is a question that will get many varying answers depending on who you ask. OEM manufacturers will commonly say anywhere from 7,500-10,000 miles under “normal use” depending on the engine and the vehicle make and model. Independent maintenance and repair facilities will usually recommend oil changes more frequently than the OEM recommendations. Maybe you have a friend or relative that never changes their oil and has “never had a problem”. What is the right thing to do? Let’s delve into some key points used in determining the proper oil change interval for your vehicle so you can make the best decision for your application.
We should start with the basics of what an oil change is and why does it need to be done. An oil change consists of replacing the oil filter with a fresh filter, draining the old oil, and filling the engine with new oil of the correct viscosity, type, and amount. During oil changes, many professional shops perform a visual inspection on your vehicle and will likely provide you with additional maintenance and repair recommendations. As a vehicle owner, the inspections and recommendations are of equal importance as the oil change itself and many times are overlooked by “do-it-yourself” individuals. The reason the oil needs to be changed is that engine oil creates a thin film of oil between the rotating engine parts and is the only thing that prevents the engine from locking up and self-destructing. The engine oil is subjected to high heat, pressure, unburnt fuel contamination, oxidation, and moisture over time; causing it to break down and deteriorate. There are six key factors that necessitate the need to change the engine oil:
Viscosity Breakdown - Viscosity is a measure of the oil’s thickness and ability to flow. Time, high temperatures, mechanical shear from rotating engine components, and oxidation cause the oil to thin (losing viscosity) or thicken (due to sludge formation) and reduces its ability to lubricate effectively, increasing friction and wear.
Oxidation and Thermal Degradation - Oxidation occurs when oil reacts with oxygen at high temperatures, forming acids and sludge. Thermal degradation happens when excessive heat breaks down the oil’s molecular structure. Prolonged exposure to high engine temperatures and workload, such as towing or aggressive driving, accelerates oxidation; creating corrosive byproducts and thickening the oil; reducing its lubricating and cooling properties.
Additive Depletion - Engine oils contain an additive package that contains detergents, dispersants, anti-wear agents, and antioxidants to enhance the performance of the oil and protect the engine components. Over time, these additives are consumed or break down. Detergents neutralize acids, but their effectiveness diminishes over time allowing corrosion. Anti-wear agents deplete, reducing protection against metal-on-metal contact.
Contamination - Oil becomes contaminated by water (from condensation), fuel (from incomplete combustion), dirt, dust, and/or metal particles (from engine wear). Contaminates build up in the oil, reducing its effectiveness. Water, unburnt fuel, and heat form sludge, while dirt and metal particles cause abrasive wear. Short trips, when the engine doesn’t fully reach operating temperature, increase condensation and fuel dilution.
Acid Buildup - Acids form from combustion byproducts and oil oxidation, especially in engines running on low-quality fuel or under high stress. Acids corrode engine components, particularly bearings and seals, leading to a higher potential for engine failure.
Sludge and Deposit Formation - Oil sludge build-up is very detrimental to the life of your engine. Oil sludge ranges from a soft, oily goo to hard, tar-like crust deposits and is the result of oxidized oil, contaminants, and degraded oil additives. It can clog oil passages, filters, and build up on engine components; which can lead to complete engine failure. The best defense to oil sludge build-up is regular oil changes with quality oil.
What about the oil change monitors built into the vehicle? Surely those are accurate and safe to follow? Unfortunately, following those monitors can lead to oil sludge build-up in the engine. Oil life monitors are computer programs designed to estimate the remaining life of the oil. Currently none of the vehicle manufacturers use a chemical sensor to sample oil condition in real time. The only way to get the accurate condition of your used oil is to take a sample of the oil and send it into a lab for analysis. Vehicle manufacturers use other engine sensors like RPM, ambient air temperature, and coolant temperature and the oil life monitor program to estimate the oil life based on vehicle use in ideal conditions with OEM specified oil. It’s the best guess and can’t account for many of the subtle operating conditions that lead to the breakdown of the engine oil. Most of those oil life monitors push the limit of the useful life of the oil and are not in the best interest of the vehicle owner. The vehicle manufacturers focus on showing low cost of ownership by extending out maintenance schedules based on “normal” use in ideal conditions and are only concerned with ensuring the vehicle makes it past the factory warranty period. When compared to the cost of replacing the engine, regular oil changes are cheap insurance and can maximize the useful life of your engine. In many cases, a well-maintained engine will outlive the structural integrity of the vehicle body.
Normal Use
What vehicle manufacturers consider “Normal use” is a very narrow window of operation. See if all these conditions apply to you and your vehicle use. Only then will your vehicle fall under the normal use category for vehicle maintenance. This list can vary from manufacturer to manufacturer, but this is a list of industry accepted parameters to operate your vehicle by to be considered acceptable “normal use” for maintenance considerations.
- Regular commuting. Driving to and from work or school, typically on paved roads and highways without stop-and-go traffic or frequent short trips. Driving far enough for the engine to reach and maintain operating temperature for a minimum of 15 minutes.
- Moderate speeds and acceleration. Driving within the posted speed limits and without consistently operating at very high speeds for extended periods. Long commutes on the Interstate would be considered operating at very high speeds. Also, avoid aggressive acceleration when driving.
- Occasional highway driving. Driving on highways or freeways for longer distances at steady speeds below 65 MPH; typically places less stress on the vehicle compared to frequent stop-and-go city driving.
- Moderate temperatures. Operating the vehicle in moderate climates without extreme temperature fluctuations. Such as driving in temperate regions without prolonged exposure to very hot or very cold conditions. Central California, for example, has pleasant sunny days, and moderate temperatures; and are good for your vehicle, but the stop-and-go traffic in that area would still exclude you from normal use.
- Light to moderate loads. Carrying passengers and cargo within the vehicle’s recommended capacity without regularly towing heavy trailers or hauling heavy loads.
- No vehicle modifications. Any modifications or accessories that change the vehicle ride height or that causes additional wind drag would not be considered normal use.
- Consistent maintenance. Regular and consistent oil changes, filter replacements, fluid checks, and inspections. Completing needed repairs promptly.
Severe Use
Most vehicles operating in the United States fall under the “severe use” category. If your vehicle operates in any of the following conditions, it would be considered “severe use” for vehicle maintenance purposes. Manufacturers often provide separate maintenance schedules for vehicles subjected to severe driving conditions, recommending more frequent oil changes, filter replacements, fluid checks, and inspections to compensate for the increased wear and tear. Following these recommendations helps maintain the vehicle’s reliability, performance, efficiency, and longevity under challenging operating conditions.
- Stop-and-go driving. Frequent starts and stops, such as city driving or heavy traffic, can put extra strain on the engine, brakes, and transmission.
- Short trips. Driving short distances without allowing the engine to reach operating temperature can lead to increased wear on engine components, exhaust systems, and emissions control systems. More frequent service intervals are needed to combat the strain on the vehicle systems and build-up of moisture in lubricating systems.
- Towing or hauling heavy loads. Transporting heavy loads, towing trailers, or carrying cargo on a regular basis can place additional stress on the engine, transmission, brakes, and suspension.
- Driving in dusty or off-road conditions. Dusty environments or driving on unpaved roads can lead to increased engine air filter and cabin air filter clogging, as well as accelerated wear on suspension components and undercarriage parts.
- Extreme temperatures. Operating the vehicle in very hot or very cold climates can affect engine performance, battery life, and fluid life. Minnesota is a perfect example of extreme temperature swings.
- Driving at Interstate speeds. Consistently driving at high speeds, such as Interstate highways, can lead to increased engine wear, higher fuel consumption, and more frequent brake and tire replacements.
- Fleet or commercial use. Using vehicles for fleet work, of any kind, can place additional stress on the engine, transmission, brakes, suspension, and tires.
The final factor in determining your oil change interval is time. Maybe you don’t drive your vehicle much and it sits in the garage most of the time. The oil still needs to be changed on a regular basis regardless of miles. The industry standard is at least once per calendar year.
So, what are the right intervals for oil changes? Unfortunately, there is no absolute correct answer that will work for everyone. Here is what we found works best for most people based on our extensive maintenance and repair history at Sanderson Auto Repair. Once you start to see the inside of engines with varied miles and service histories, you begin to see what service intervals keep the engine in the best working condition. These recommendations are what I personally follow on my own vehicles. Vehicles that require full synthetic oil I recommend performing an oil change every 5000 miles or once per calendar year. I also rotate the tires at the same time. Vehicles recommending regular oil I recommend changing the oil every 3000 miles or once per calendar year. Personally, I prefer to upgrade to full synthetic oil in all my vehicle engines. It’s better for the engine and coincides with recommended tire rotation intervals. A properly serviced and maintained modern engine can easily remain reliable and in good working order for over 300,000 miles. Abused and neglected engines are sometimes lucky to make 100,000 miles. A $75 oil change and inspection a few times a year is always more affordable than $7000+ to replace a failed engine. Don’t forget the other vehicle systems lubricated by fluids like the transmission, power steering, transfer case, differentials, brakes, and cooling system. Each system has its own service intervals depending on how you use the vehicle. Never skimp on fluid maintenance if you want to keep your vehicle reliable and trustworthy for many years and miles down the road.