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The possible problem of inadequate low-temperature engine oil pumpability was considered in the early '60s and grew into prominence in the late '60s and early '70s with the success of the automotive industry in improving low-temperature engine startability. Reported incidents of field pumpability problems in the early '70s led to an extensive ASTM study using several cold-rooms and a number of reference oils. This study confirmed the previously anticipated existence of two forms of pumpability problems — flow-limited pumpability caused by higher viscosities and air-binding pumpability caused by engine oil gelation under certain cooling conditions.
Of these two forms of engine pumpability failure, air-binding was the primary threat to engine life. This was a consequence of the fact that some engine oil formulations could be induced to gelate at temperatures well above viscosity-limited temperatures. Despite these extensive cold-room studies and the development of a Mini-Rotary Viscometer bench test closely simulating the cold-room results, the work did not prepare those studying the problem area for the disastrous winter of 1980–81 when several million dollars of engines failed in the field as a result of air-binding oil effects.
In renewed efforts to develop viable bench tests correlating to these field-failing engine oils representing real world conditions, two instruments emerged: one in 1982 called the Scanning Brookfield Technique and the second, a further adaptation of the original MiniRotary Viscometer (called the MRV TP-1), in 1985.
Another recent ASTM cold-room study has confirmed improved startability and brought into question whether or not modern engines are less prone to air-binding.
At the same time, new pressures on both automotive and heavy-duty diesel engines have just come to attention as a consequence of long drain intervals and their effects on engine oil oxidation. It has been shown that such intervals can have serious effects on the engine through the coupling of both viscosity-limited and air-binding characteristics, In a similar manner, high soot loading in diesel engines recently redesigned to reduce oxides of nitrogen has produced further low-temperature pumpability problems and the associated needs to understand the chemistry and rheology of such oils at these temperatures and to find ways of reliably and repeatably measuring these phenomena.
Pumpability, oxidation, air-binding, viscosity-limited, flow-limited, Brookfield Viscometer, Gelation Index, Gelation Index Temperature, D 5133, Scanning Brookfield Technique, MiniRotary Viscometer, cold-room engine tests
Director R&D, Savant, Inc., Midland, MI