Did you know that your motor oil is responsible for approx 40% of total engine cooling?
From Kevin Ferrick (Director, GIS Product Programs, API.ORG)
From Kevin Ferrick (Director, GIS Product Programs, API.ORG)
Many people assume that engine cooling is accomplished only through the action of the water-antifreeze mixture used in the cooling system. In fact, this mixture does only about 60 percent of the cooling job. It cools several engine parts—the cylinder heads, the cylinder walls, and the valves. The crankshaft, the main and connecting rod bearings, the camshaft and its bearings, the timing gears, the pistons, the turbocharger, and many other components of the engine rely directly on the motor oil for cooling. All of these parts have finite temperature limits that must not be exceeded. Some can tolerate fairly high temperatures while others, such as the bearings, must run relatively cool to avoid failure. An ample supply of cool oil must be delivered to the parts, where the oil picks up the heat from the parts, carries it back to the crankcase, and transfers it to the surrounding air.
Some idea of the temperatures an oil experiences may be helpful in understanding the role of oil as a coolant. Combustion temperatures are 1093–1649°C (2000–3000°F. Certain parts of the valves may reach temperatures of 538–1093°C (1000–2000°F). Piston temperatures can reach 538°C (1000°F), and this heat travels down the connecting rods to the rod bearings. Tin and lead, which are the more sensitive of the metals commonly used in bearings, become very soft around 177°C (350°F). Tin melts at 232°C (450°F), while lead will melt at 327°C (620°F). After warmup, crankcase oil temperatures reach 93–135°C (200–275°F), and oil is supplied to the bearings at this temperature. The oil picks up heat at the bearings and leaves them at temperatures around 121–149°C (250–300°F), well below the critical temperatures of bearing failure. The continual cooling of the oil by recirculation to the crankcase is essential to maximizing bearing life.
To keep this cooling process working, the engine must constantly circulate large volumes of oil to the bearings and other engine parts. If the oil supply is interrupted, either by deposit formation, oil pump problems, or low crankcase oil levels, for example, the bearings and other parts can heat up rapidly from increased friction and combustion temperatures or decreased cooling by the oil. A bearing failure is often referred to as a “burned-out bearing” because temperatures rose high enough to actually melt the bearing metal.
While only a small quantity of oil is required at any one time and any one place to provide lubrication, the oil pump must circulate many gallons of oil per minute in order to achieve lubrication and properly cool these parts. Chemical additives and the physical properties of the oil have little effect on its ability to provide adequate cooling. What is critical is the continuous circulation of large volumes of oil throughout the engine and over hot engine parts. This is made possible through the use of an oil of the right viscosity for that engine, high-volume oil pumps, and oil passages adequate to handle the required volume of oil. These oil passages cannot do the job properly if they are allowed to become partially or completely clogged with deposits. When this happens, the oil cannot circulate or cool properly, and early engine failure may result. This is yet another reason for using the proper performance oil and for changing the oil before the contaminant level becomes too high. Proper cooling also requires that the oil level in the crankcase never be permitted to remain below the “add oil” line on the dipstick.