How often should you change the oil in your engine? On most new vehicles, the factory recommended interval for changing the oil and filter is typically once a year or every 7,500 miles in passenger car and light truck gasoline engines. Some OEMs even recommend 10,000 mile oil change intervals. A growing number of OEMs make no specific mileage or time recommendation and use oil monitoring software to turn on an oil change reminder light when the oil is estimated to need changing. For diesel engines and turbocharged gasoline engines, the recommended interval is typically every 3,000 miles or six months.
If you read the fine print in your owners manual on vehicles where a specific mileage/time recommendation is made, you'll often discover that the once a year, 7,500 mile oil change is for vehicles that are driven under "ideal" operating circumstances. What most of us think of as "normal" driving is actually "severe service" driving.
Severe service driving includes:
Frequent short trips (less than 10 miles, especially during cold weather)
Stop-and-go city traffic driving
Driving in dusty conditions (gravel roads, etc.)
Driving at sustained highway speeds during hot weather.
For severe service driving (which is what most of us do), the most common recommendation is to change the oil every 3,000 miles or six months (which ever comes first). This is especially important on older, high mileage (over 100,000 miles) engines.
For maximum protection, many people change their oil every 3,000 miles or three to six months regardless of what kind of driving they do. But some would say this is excessive maintenance. Changing the oil every 3,000 miles is probably not necessary on a newer vehicle with a low mileage engine, especially if it is driven more than 10 miles one-way daily or is used primarily for highway driving or long distance commuting.
A newer engine with little or no wear can probably go 5,000 to 7,500 miles between oil changes with no harm. But in my opinion, pushing the oil change interval beyond 7,500 miles is asking for trouble, especially if an engine has more than 75,000 miles on it, or it operated under "severe" conditions as described above.
As an engine accumulates miles, blowby increases. This dumps more unburned fuel into the crankcase which dilutes the oil. This causes the oil to break down. So if the oil is not changed often enough, you can end up with accelerated wear, oil sludging and all the engine problems that come with it: loss of performance & fuel economy, and increased emissions and oil consumption.
To find out what ASE certified Master Technicians said about oil change intervals in a June 2006 survey, Click Here.OIL REMINDER LIGHTS
General Motors and a number of European vehicles have done away with recommended oil change intervals altogether and now use an "oil reminder" light to signal the driver when an oil change is needed. On some of these (Volkswagen, Audi, Mercedes Benz, BMW and Volvo), a scan tool or a special service tool is required to reset the oil service reminder light. On others, there is a manual procedure for resetting the oil reminder light.
DO NOT IGNORE THE LIGHT! When the light is on, it is time to change the oil.
The oil reminder systems estimate oil life based on engine running time, miles driven, ambient temperature, coolant temperature and other operating conditions. On some of these vehicles, the light may not come on until 10,000 miles or higher! But keep in mind that most of these engines are factory-filled with higher quality synthetic oil, so be sure to replace same with same when the oil on these engines is changed if you are going to rely on the oil reminder light alone rather than a mileage/time interval.
OIL ANALYSIS
One way to know for sure when the oil needs to be changed is to have the oil analyzed at 3,000, 5,000, 7,500 or 10,000 miles. Many fleets do this to optimize their oil change intervals. A small sample of oil (3 to 4 oz.) is taken from the engine, sealed in a bottle and mailed to a laboratory for analysis. The lab runs a series of tests to determine the properties of the oil and the contaminants that are in the oil. A report is then mailed back with a recommendation as to whether or not the oil is still good.
Having your oil analyzed is not something you need to do all the time. Checking it once or twice should help your determine the optimum oil change interval for the type of driving you do. The cost for oil analysis is usually less than $25, and there are a number of companies who offer such services: Blackstone Laboratories, Oil Analyzers Inc., Insight Services and others.
NEW OIL MONITORING TECHNOLOGY
The latest technology for letting you know when your oil needs to be changed is electronic sensing. An oil monitoring technology originally developed for the military called IntelliStick is now available to consumers. The sensor replaces the dipstick and provides real time monitoring of the oil's true condition. This eliminates the guesswork and uncertainty that exists with recommended service intervals or oil reminder lights.
The IntelliStick uses a simple, patented conductivity test that applies low voltage with slow varying waveforms across two sensor arrays. The sensor measures changes in the electrochemical current flow caused by additive package depletion and impurities that accumulate over time in the oil. As more additives are depleted, most notably antioxidants and detergents, the oil's conductivity changes, which leads to a corresponding reduction in the IntelliStick sensor reading.
The IntelliStick has a transponder at the top of the dipstick that communicates with any Bluetooth-enabled PDA, cell phone or laptop so you can check the condition of your oil at any time.
For more information about this new product, visit the IntelliStick website.
WHY OIL NEEDS TO BE CHANGED
Regardless of what type of oil you use (conventional, synthetic or synthetic blend), all motor oils eventually wear out and have to be changed (actually, it's the additives that wear out more so than the oil). As the miles add up, motor oil loses viscosity and gets dirty. The oil no longer has the same viscosity range it had when it was new, and it contains a lot of gunk (moisture and acids from combustion blowby, soot, dirt and particles of metal from normal wear). You can't really tell much about the condition of the oil by its appearance alone because most oil turns dark brown or black after a few hundred miles of use.
The oil filter will trap most of the solid contaminants, and the Positive Crankcase Ventilation (PCV) system will siphon off most of the moisture and blowby vapors, if the engine gets hot enough and runs long enough to boil the contaminants out of the oil. Even so, after several thousand miles of driving many of the essential additives in the oil that control viscosity, oxidation, wear and corrosion are badly depleted. At this point, the oil begins to break down and provides much less lubrication and protection than when it was new.
If the oil is not changed, the oil may start to gel or form engine-damaging varnish and sludge deposits. Eventually this can cause your engine to fail! Oil sludge can damage engine bearings, piston rings, cylinder walls, valve guides and lifters.
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