Changing the oil in your car is a relatively easy procedure that can save considerable cost over the long run. As such, one of the most frequent questions we are asked by people interested in doing their own repairs on their car is “How often should I change my oil?” It’s a great question, with a not so simple answer. As such, we will break down some of the basics as far as how many miles you should go between oil changes.
Why Do You Need To Change Your Oil?
Oil is the lifeblood of your car’s engine, in that it protects all of your engine’s internal components from wear. Without motor oil, your car’s engine would last about 15 seconds of run time before seizing up and stopping with massive permanent damage to internal components. With oil to protect your motor, you can easily exceed 100k or 200k miles before needing to replace any major internal components.
Over time, oil tends to degrade and break down meaning its viscosity tends to become reduced with a corresponding reduction in protection for your internal engine components. This happens for a couple of reasons. First, this is a natural process that occurs just as a result of time, heat, and exposure to air. Conventional oil tends to break down the most quickly, while synthetic oil tends to last significantly longer. The other enemy of oil is contamination. As your engine runs, your oil gets contaminated and diluted with exhaust gas blow by, raw fuel, water, carbon, and metal particles. Your oil filter can remove much of the particulate, but over time the other contaminants add up and start to change the properties of your oil. Before this happens, you’ll want to get your trusty oil filter wrench and your best oil drain pan out and swap that old oil and oil filter out.
Note: Any time you change your oil you should also change your filter at the same time.
How Often Should You Change Your Oil When Your Car Is Under Warranty?
When your car is under warranty, the answer is pretty simple. You should change your oil based on what is listed in your car’s user manual or dealer service plan and furthermore you should use the specific motor oil recommended by the vehicle manufacturer. Deviating from the scheduled maintenance plan in any way can void your warranty and potentially cost you big bucks.
While we recommend sticking with what the manufacturer says, there is a caveat. A growing trend in the automotive industry is to offer free maintenance throughout the first few years of ownership. BMW, Mini, Volkswagen, and many other auto manufacturers have been known to offer deals like this, either through the manufacturer or through the dealer network. Obviously it is in the best interest of manufacturers to stretch the maintenance interval out as long as possible to reduce the number of services needed to save cost. While these service intervals have been tested through the warranty period, if you are the type of person who drives a car until the wheels fall off, you may consider changing your oil more frequently if your warranty allows.
How About When Your Car Is Out Of Warranty?
When your car is out of warranty, the rules change. You can’t void a warranty that you no longer have, so you have free reign when it comes to making the decision of when to change your oil. Typically, we recommend change intervals that are more frequent than the dealer service interval in attempt to maximize the lifespan of your engine.
When Using Conventional Oil
When using conventional oil, we typically recommend changing your oil every 3000 miles as a general rule of thumb. Conventional oil tends to be more frequently used in older cars which are more subject to contaminating oil than newer cars which are built to much tighter tolerances. In addition, conventional oil tends to break down more quickly than synthetic, so you can’t wait as long between changes.
When Using Synthetic Oil
When using synthetic oil, we typically recommend changing your oil every 7500 miles or so, depending on the vehicle. Since older vehicles tend to more quickly contaminate oil, we recommend shortening this interval to 5000 miles if you have an older car that was originally designed to run conventional oil. We should also note that with a longer interval comes greater responsibility to make sure your oil level stays topped off. Short intervals are more forgiving if you forget to check your oil level regularly since there is a higher change you will replace your oil before the level gets too low.
Note: While the increased oil change interval might be desirable with synthetic oil, it should be noted that synthetic oil tends to find leaks more easily. Due to the difference in molecular sizes, synthetic oil can sometimes find pathways out of your engine and onto your garage floor that conventional oil can’t. In other words, if you choose to swap your leak free engine from conventional to synthetic, you may find that you start to see oil leaks that weren’t present before.
Other Special Circumstances
Some special circumstances exist where you can’t follow general guidelines or rules of thumb. If you live in a place that has extremely cold winter weather, you may need to run a lower viscosity oil in the winter than you do in the summer, which means you need to change your oil every six months or so regardless of miles.
Another special case is if you have a high performance car or particularly a car that sees regular track or autocross time. These cars require oil changes more frequently (we change ours after every track day).
A final special circumstance is that you just don’t drive the car very often. This is relatively common with collector vehicles and garage queens. As mentioned previously, time and exposure to air alone are enough to degrade oil. Due to this, if you only drive a few miles per year you should still plan on at least changing your oil annually to make sure you always have good oil in your engine.
We hope this summary of recommended intervals has been helpful. Please note that these are just rules of thumb and while they pertain to most people, they may not pertain to your special individual case. If you are ever in doubt, we suggest asking your mechanic or consulting your car’s user manual. Happy wrenching!