Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/629709
Figure 1. Piston ring-pack oil flow (Ref. Shell) FROM THE FIELD A u t o m o t i v e H UNDERSTANDING igh consumption of engine oil is almost always a symptom or consequence of another condition of even greater impor- tance. This article will address this issue from the standpoint of oil loss through combustion pathways (versus leakage). While the focus will be more on diesel engines used in industrial and commercial service, much of what will be discussed applies equally well to personal automobiles and natural gas engines. By itself, oil consumption is a well-known source of harmful emissions to the atmo - sphere (see the sidebar on page 4). Unburned or partially burned oil is released through the exhaust path in the form of hydrocarbons and particulate contamination (soot). Addi- tionally, motor oil anti-wear additives are known to poison or at least impair the performance of catalytic converters. The more oil consumed through the combustion chamber, the greater this poisoning risk/ effect. This escalates the environmental impact further. The causes of high oil consumption are many and complex. Because this consump- tion is symptomatic of other conditions, there is a need to be aware of changes in the oil consumption rate. These changes should be viewed in the context of other data and factors, including oil analysis, visual exhaust, engine service life (from last rebuild), boost pressures, running temperature, load/RACK, blow-by and operating conditions. Oil anal- ysis will be discussed in terms of the correlation and meaning of common trends and how they might be useful for trouble- shooting purposes. Causes of High Oil Consumption Understanding oil transport mecha- nisms is necessary to prevent oil from going where it shouldn't. Loss of engine oil is influenced by the engine's design and the operating conditions. Oil consumption primarily occurs near or through the combustion chamber, either downward through valves or upward past the piston ring-pack. Oil Mobility and Consumption Through Engine Valves Oil collecting on the stems of intake valves is sucked into the combustion chamber during normal operation. Hot exhaust gases burn oil on stems of the exhaust valves. If there's too much clear- ance between the valve stems and guides, the engine will suck more oil down the guides and into the cylinders. This could be AS I SEE IT Jim Fi t ch | Nori a Corpor at ioN How Engines CONSUME OIL 2 January - February 2016 | www.machinerylubrication.com