LO 10-8 Describe the purpose of scheduled oil sampling and outline the steps to properly obtain an oil sample

1. Scheduled Oil Sampling

Scheduled Oil Sampling

Oil quality sensors, which are electrical devices that measure the amount of soot loading in engine oil, are now available to measure the condition of lubrication oil but are not mature in terms of the technological sophistication needed to perform condition-based oil changes. Still, such a sensor can help alert the operator when oil quality falls outside specified parameters as a result of the oil exceeding its useful life or a symptom of an engine problem. Additionally, one of several sensor technologies accurately measures soot, which thickens oil viscosity, absorbs oil additives, and contributes to engine wear. The sensor operates like a variable capacitor, using oil as the dielectric element. By measuring alternating current (AC) conductivity across the sensor at frequencies of 2–5 MHz, the sensor evaluates the dielectric strength of oil. This variable changes in proportion to oil quality.

In the absence of any sensor capable of comprehensively measuring oil quality, scheduled oil sampling (SOS) is recommended. In SOS, a sample of engine oil is obtained from the engine and sent out for analysis Figure 56,Figure 57 and Figure 58. SOS can provide extremely detailed analysis of the condition of the engine and the quality of the engine oil TABLE 10-8.

FIGURE 10-56: A clean, representative sample of oil is removed for analysis. During scheduled oil sampling, oil can be removed from the oil pan or engine oil gallery.

FIGURE 10-57: A scheduled oil sampling bottle is mailed for analysis. Results are available through reports accessed on the Internet.

FIGURE 10-58: An oil sample bottle can collect a sample of filtered oil from a running engine using a Schrader valve located in the engine oil gallery.

1.1. Oil Life Algorithm Systems

Oil Life Algorithm Systems The engine ECU continuously monitors engine operating conditions to determine when to change oil. Software-based calculations use a formula or algorithm with input variables for engine operating conditions to determine oil life. Because oil degradation is associated with combustion events, analyzing combustion conditions can accurately determine when oil life has reached its maximum value. For example, when a cylinder fires, a small amount of oil is exposed to combustion and destroyed. Combustion gases containing acids, unburned fuel, water, and other byproducts leak past the piston rings and react with the engine oil. Diesels tend to generate much more soot and acidic combustion blowby in the crankcase. It is also known that oil temperature exerts a strong influence on the deterioration of oil quality Figure 59. As oil temperature increases, the rate of oxidation accelerates, which can lead to oil thickening. Turbochargers subject motor oils to high temperatures and are more prone to form engine deposits. Colder oil temperatures increase the concentration of oil contaminants, such as fuel and water. Depending on the vehicle and engine type, each engine receives its own unique algorithm to determine engine oil life.

FIGURE 10-59: Engine oil life is influenced by its operating temperature.

1.2. Excessively Low and High Oil Pressure

Excessively Low and High Oil Pressure

Virtually all HD, diesel-powered vehicles use a dash-mounted oil pressure gauge. Although engine protection systems shut down the engine, derate, or at least warn the driver of excessive oil temperature or low oil pressure, the presence of a prominent dash gauge underlines for the driver and the technician the importance of monitoring this engine parameter.

Low oil pressure can lead to oil starvation of critical engine components, which can cause seizure or rapid, premature wear. It is important to differentiate between low and abnormally low oil pressure. As engines wear normally, bearing clearances become wider, which results in more oil pump volume and lower oil pressure. This happens because pumps move oil volume while restrictions to volume (e.g., normal bearing clearances) produce pressure. Low oil pressure, or a drop in oil pressure from operating speed, is not necessarily abnormal. When oil becomes hot, it thins and causes a normal drop in pressure. Abnormal pressure is defined by the manufacturer and measured when the engine oil is at operating temperature, preferably with an accurate, direct reading mechanical gauge. The potential for reporting the wrong oil pressure due to a defective sending unit or dash gauge requires another independent measuring device to validate a dash gauge measurement. Before confirming a low oil pressure complaint, the OEM’s specification must be consulted; these numbers may surprise technicians and drivers alike because they are often lower than expected. The oil level, viscosity, and presence of dilution with fuel should be checked when investigating low oil pressure complaints.

Subsequent to preliminary checks, diagnosis of low oil pressure should follow an OEM fault tree to differentiate problems caused by blocked oil filters, plugged oil coolers, internal oil leaks, worn oil pumps, and faulty pressure-regulating valves and thermostats. Worn engine bearings are best checked by removing several main and rod bearing caps to determine whether the top layer of babbitt is worn away. Some engines may use an oil viscosity-regulating valve to correct oil pressure when the oil is cold or thickened. These valves can fail and produce a rapid drop in oil pressure only after the engine begins to warm up.

When investigating any oil pressure complaint, a technician should note where the dash sending unit is located in the lubricating system circuits. Generally, most sending units are located after the oil pump and before the oil filter. Watching little or low oil pressure for many minutes that only slowly rises after an engine starts cold can cause alarm for a driver; locating the sending unit between the oil pump and the filter minimizes occurrences for concern.

Complaints about low oil pressure should be verified when the engine is at operating temperature. Idle oil pressure and high idle oil pressure can be compared against the manufacturer’s specifications Figure 60.

FIGURE 10-60: Low oil pressure diagnosis process.

High oil pressure and abnormally high oil pressure need to be differentiated from normal oil pressure following procedures similar to those used to investigate low oil pressure. The high system pressure must be validated with an independent, accurate pressure gauge. While plugged filters, thick oil, and even tight engine bearings or cam bushings can produce high oil pressure, abnormally high pressure is defined by OEM specifications. Generally, abnormally high oil pressure is caused by a defective oil pressure-regulating valve. Replacing the valve after visually inspecting it is often the only effective diagnostic procedure in this case. Operation of the valves and oil pump are evaluated using a direct reading pressure gauge in the main oil gallery. A high oil level can cause oil to foam because the oil contacts the rotating crankshaft, thereby aerating the oil. As a result, the oil cannot properly pressurize and produces erratic readings as well as rough running, stalling, and other related drivability problems with HEUI fuel systems.