If engine lubricating oil viscosity reduced and temperature increase over the highest limit what consequences could be expected?
Overheating
The formation of an explosive vapor from lubricating oil is greatly accelerated by a rise in the temperature of the lubricating oil. A rise in temperature may be due to such factors as an insufficient circulation of the oil, inadequate cooling of the oil, a faulty temperature-regulating valve, overloading of the engine, or damaged or excessively worn parts. In addition to creating explosive vapors, overheated lubricating oil can have other serious effects. The viscosity of the lubricating oil will be greatly reduced, and the tendency to form acids will be increased. Immediate steps must take to correct any problem associated with overheated lubricating oil. The temperature of the lubricating oil must be maintained within the range of values specified in the technical manual for your engine.
Dilution
Dilution of engine lubricating oil with diesel fuel or increases the tendency toward vapor formation in the crankcase because both of these fuels have lower flash points than lubricating oil. Petroleum products vary greatly in their flash points. (The flash point is the minimum temperature at which a product of petroleum gives off sufficient flammable vapors to ignite or momentarily flash). In general, gasoline gives off sufficient vapor to ignite at all temperatures well below freezing; diesel fuel gives off vapor in sufficient quantities to ignite when it is heated to approximately 140F. On the other hand, a lubricating oil must be heated to a much higher temperature (325F to 510F, depending on the grade of the oil) before it reaches its flash point. It be should be remembered that dilution alone cannot cause a crankcase explosion. It may, however, contribute to making an explosion possible.
Dilution of engine lubricating oil may be caused by a variety of troubles. In general, dilution of the lubricating oil in diesel engines may result from worn or stuck rings, worn liners or pistons, fuel leaks, or leaky nozzles or injectors. Remember that, even though an engine is in good condition, dilution will occur during continuous engine operation at low speeds and under idling conditions. Under these conditions of operation, dilution occurs as a result of the blow-by of unburned fuel particles that accumulate in the combustion spaces. As determined by tests, any diesel lubricating oil that is contaminated by more than 5 percent fuel should be discarded.
