Eye on electronics

Motor,  Mar 2003  by Dale, Mike

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As the sophistication of on-board engine oil condition monitoring systems increases, one more reason for vehicle owners to raise the hood may be eliminated.

In one form or another, the majority of today's new cars have an oil condition monitoring system on board. These systems are intended to protect against engine damage and save oil by extending service change intervals. The science says oil changes could be extended to 10,000 miles or more, depending on driving conditions. If this were true, millions of gallons of motor oil wouldn't have to be used or disposed of.

GM, with the installation of its Intellek oil monitoring system, has changed its recommended service interval to 10,000 miles or whenever the Change Oil Soon (COS) light comes on. European makers such as BMW and Saab recommend 15,000 miles. Ford has offered as an option a settable, odometer-driven oil reminder light on Windstar and a few other models. In the heavyduty truck industry, Mack recommends 50,000-mile oil changes. Meanwhile, the quickie oil change franchises have been sticking with their position that everyone drives under "severe" conditions and that the oil should be changed every 3000 miles or three months.

This is all about the two basic approaches to vehicle service. One approach is to service the vehicle based on time, mileage and that very tricky phrase "severity of use." There are two risks associated with this: At one extreme, the oil will be changed more often than is necessary. At the other, the oil becomes contaminated with coolant or fuel, and its lubricating properties could be compromised to the point of engine failure before the problem is discovered during a routine oil change.

The better approach to vehicle service is to replace the oil-or for that matter, any component-only when its useful life is over. This requires diagnosis. For applications like heavy-duty trucks and road-building machinery, where the crankcase fill is measured in gallons, testing the oil before changing has been routine for years. Samples are checked using a variety of very sophisticated lab instruments to measure the viscosity, total acid number and particle/soot contamination levels, and to check for the presence of heavy metals, etc. Clearly, this is too complicated and expensive for normal automobiles.

In normal engine operation, the oil itself does not "wear out"; it gets contaminated. Normal contamination includes combustion byproducts such as acids, ash and soot. Abnormal, and possibly engine-life-threatening, contaminants include water, gasoline and antifreeze.

Oil does more than just lubricate. You should know that as much as 25% of what's in that can of oil you pour into an engine didn't come from an oil well. An additive package is included to help the lubricant deal with the various forms of contamination that occur normally. Primary additives are detergents, viscosity index improvers, friction and wear modifiers, pour point depressants, antioxidants, corrosion and rust inhibitors and antifoaming agents.

The problem is that the additives get used up during normal engine operation. Knowing whether the oil really needs to be changed is about knowing to what extent these additives have been used up and to what extent there is contamination of the oil that the additives were not able to deal with. How quickly the additives are used up is directly related to the severity of the driving conditions. Since this is a variable with every vehicle and driver, a method is needed to measure the depletion.

There are some other things that would be useful to know about the condition of the engine oil. Oil that's operating at excessive temperatures (above 350 deg F) is prone to oxidation and breakdown. One of the selling points of synthetic oils is that they have a much higher safe operating temperature (600 deg F). Oil fill levels are also important in terms of both lubrication and engine cooling. A good oil condition sensor should also be able to warn of temperature and fill level problems.

There are several different technologies and combinations of technology incorporated into production oil condition monitoring sensors. These can be divided into direct and indirect measurement/monitoring techniques.

One side of this is in the ECM and its software. The ECM can store information such as engine operating temperature, time of use, engine load factors, trip distance and other parameters. Based on OEM engine testing, computer formulas called algorithms can be constructed. When engine operating circumstances are entered into the algorithm and the computer crunches the data, the condition of the oil can be predicted. GM started using this method in 1988.

Software solutions are inexpensive in that they use existing sensors and computer space. Furthermore, they can warn those drivers who never do any maintenance that an oil change is needed. A disadvantage is that they have no direct connection to the oil. Fuel, water and coolant contamination could be present and the system would not be able to detect it. The algorithm is based on engine and dyno testing that assumes certain driving conditions. The software won't know if you spend most of your time driving down dusty roads in Kansas or between snowbanks in Maine.