Tänud: cadillacforums.com
How long will oil last in an engine? What reduces the oil’s effectiveness? When should it be changed?
Lubrication engineers perform a number of tests to answer these kinds of questions.
Vehicles are operated under prescribed conditions, and periodically a sample of the oil is taken into the laboratory for analysis. When
the condition of the oil is no longer satisfactory,
the mileage is noted.
From controlled testing like this, engineers in the past have determined two sets of mileage numbers, one number for normal driving and the other for severe conditions.
Severe conditions can mean that the vehicle is driven hot (for example, pulling a trailer up a mountain) or is driven such that the oil never warms completely (for example, trips less than 5 or 10 miles in a winter climate). It is then up to the owner to decide whether their own driving is normal or severe and to change the oil accordingly.
Now, science and technology have found a way of taking the guesswork out of the picture.
GM is installing an oil life monitor in an increasing number of new vehicles. Using a simple indicator lamp or readout on the instrument panel, this system notifies the driver when to change the oil.
Additives
Straight oil is not an ideal lubricant in an engine. A package of additives is needed to give the oil properties it does not naturally have or to enhance its natural properties.
Some of the tasks accomplished by additives:
- viscosity modifiers, to keep the oil the proper thickness over a wide range of operating temperatures
- anti-oxidant, to keep the oil from thickening
- corrosion inhibitors, to protect engine components
- anti-wear
- anti-foam
- detergents, to suspend solid particles.
What Makes Oil "Wear Out?"
Water in oil, resulting from extreme short-trip driving, photographed through a transparent oil pan.
If you were to start out with a crankcase full of fresh, clean oil, and drove the vehicle for a period of time, eventually the oil would have to be changed. During this time, what can change fresh oil into "worn out" oil?
First, dilution. When gasoline is burned in the combustion chamber, the by-products include a lot of water. Some of this water can find its way into the crankcase through piston ring blow-by. If the engine is cold, and if combustion is not perfectly complete, a small amount of acid is formed. It, too, can blow-by into the oil. You don’t need to be a top-notch scientist to realize that water and acid aren’t good things to pump through the lubrication system of the engine. If an engine is run long enough for the engine oil to warm, the water and acids will evaporate and not accumulate.
But, during very short trips in cold weather, water and acids can enter the engine oil and cause the oil to "wear out."
Second, the degradation of the oil and its additives. We mentioned earlier that a number of additives are put into oil to improve its performance. If these additives are degraded or decomposed, the oil is no longer capable
of doing all of its jobs properly. Oil with degraded additives can become thick and dark. Additives become degraded by exposure to extreme heat. There are two places a lot of heat can reach the oil. One is near the combustion chamber. Oil at the top piston ring is exposed to very high temperature.
And some bearing surfaces can also put a lot of heat into the oil at high operating temperatures.
So, degradation of additives from high temperature operation is the second factor that can cause oil to "wear out."
How Can Operating Conditions be Used to Predict Oil Life?
Using carefully controlled laboratory tests, it’s possible for lubrication engineers to measure how long it takes to dilute engine oil during cold operation. And it’s possible to measure how long it takes for high temperature to degrade the additives.
We usually think of measuring time in hours and minutes, but for an engine, the amount of revolutions it has run is also a good measure. So for the purposes of oil life, time is measured in engine revolutions.
Engineers like to talk in terms of models.
A model is a way to describe something mathematically. It’s possible to create an oil life model that very carefully matches the results of analyzing the oil in a laboratory.
The oil life monitor, then, is based on a model. A computer chip in the Powertrain Control Module is loaded with a certain number of engine revolution counts. The count for each engine/vehicle combination is determined by testing. As the engine runs, each revolution is subtracted from the remaining count in the oil life monitor. When the count reaches zero, the instrument panel light comes on. But, here’s the clever part. When the various input sensors detect that the engine is running under either cold or hot conditions, it subtracts extra counts (penalties) for each engine revolution. So, the conditions that cause the oil to "wear out" make
the counter run down faster.
When the oil is changed, it’s necessary to reset the oil life monitor and the
countdown begins again.
NOTE: Synthetic oil resists "wearing out" better than mineral oil, so the oil life monitor is set to account for this, but only on vehicles that are specified for synthetic oil from the factory -- the Corvette, for instance. Using synthetic oil in other vehicles is certainly not harmful, but the oil life monitor will continue to count down as though the engine contained
mineral oil.
Oil Life Monitor - mis loom ta on ja kuidas teda süüa.
How often should engine oil be changed?
- 3,000 miles
- 5,000 miles
- 7,500 miles
- 10,000 miles
Actually, all of these are correct, depending on operating conditions. Oil life is affected by many factors other than just miles driven. The type of driving, temperature, and engine load all play a part.
That’s why GM has developed the GM Oil Life System, an electronic watchdog that keeps track of all these variables and notifies the driver when it’s time to change oil. We first told you about the GM Oil Life System in the March 2000 TechLink. Since then, the system has become standard equipment on nearly all GM products.
Briefly, the Oil Life System is programmed with a certain number of engine revolutions. As the engine runs, this number is reduced until it reaches zero, and the Oil Life light or message comes on. But there’s more. Operating the engine under low or high temperatures, and under high load conditions subtracts (penalizes) extra revolutions, so the light comes on sooner.
Changing engine oil according to actual need rather than an inflexible schedule provides several benefits.
First is simpified determination about when to change oil. No more decisions about “normal” conditions vs. “severe” conditions. Second is reduced operating costs for GM’s customers, who now have to change oil only when it’s needed. Third is minimizing the amount of used oil that must be disposed of. And fourth, engines will always be running with sufficiently fresh oil, for long life.
- 3,000 miles
- 5,000 miles
- 7,500 miles
- 10,000 miles
Actually, all of these are correct, depending on operating conditions. Oil life is affected by many factors other than just miles driven. The type of driving, temperature, and engine load all play a part.
That’s why GM has developed the GM Oil Life System, an electronic watchdog that keeps track of all these variables and notifies the driver when it’s time to change oil. We first told you about the GM Oil Life System in the March 2000 TechLink. Since then, the system has become standard equipment on nearly all GM products.
Briefly, the Oil Life System is programmed with a certain number of engine revolutions. As the engine runs, this number is reduced until it reaches zero, and the Oil Life light or message comes on. But there’s more. Operating the engine under low or high temperatures, and under high load conditions subtracts (penalizes) extra revolutions, so the light comes on sooner.
Changing engine oil according to actual need rather than an inflexible schedule provides several benefits.
First is simpified determination about when to change oil. No more decisions about “normal” conditions vs. “severe” conditions. Second is reduced operating costs for GM’s customers, who now have to change oil only when it’s needed. Third is minimizing the amount of used oil that must be disposed of. And fourth, engines will always be running with sufficiently fresh oil, for long life.
How the Oil Life System Works
GMOLS is a computer-based algorithm that assesses engine combustion events, temperature, vehicle use, and other parameters to determine optimum oil change intervals. Oil changes are now called for when actually needed, instead of depending on generic time or mileage interval tables. Mild highway driving in a mild climate can yield change intervals of 7,000 miles (11,000 km) or more, and as high as 12,000 miles (19,000 km) for some vehicles. Short trip driving in cold weather may reduce intervals to 3,000 miles (5,000 km) or less. Most people driving a combination of city and highway will likely see intervals of about 6,000 miles (10,000 km).
When GMOLS determines that an oil and filter change is needed, the driver is notified by a Change Oil message on the instrument panel. Oil should be changed within 600 miles (1000 km).
TIP: The Oil Life System must be manually reset when the oil is changed.
GMOLS is a computer-based algorithm that assesses engine combustion events, temperature, vehicle use, and other parameters to determine optimum oil change intervals. Oil changes are now called for when actually needed, instead of depending on generic time or mileage interval tables. Mild highway driving in a mild climate can yield change intervals of 7,000 miles (11,000 km) or more, and as high as 12,000 miles (19,000 km) for some vehicles. Short trip driving in cold weather may reduce intervals to 3,000 miles (5,000 km) or less. Most people driving a combination of city and highway will likely see intervals of about 6,000 miles (10,000 km).
When GMOLS determines that an oil and filter change is needed, the driver is notified by a Change Oil message on the instrument panel. Oil should be changed within 600 miles (1000 km).
TIP: The Oil Life System must be manually reset when the oil is changed.