Affects Fuel Consumption Cooling system efficiency may also account for
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the small difference, reported by some operators, between the fuel consumptions of dieselpowered and petrol-engined vehicles engaged on stop-start work, which represents a type of service in which the diesel should excel. High friction losses in a petrol engine running at low temperatures may be partly offset by an improvement in volumetric efficiency. Although a diesel engine also benefits from aspirating a greater weight of combustion air at higher loads, reduced combustion-chamber temperatures are particularly unfavourable to thermal efficiency at low loads.
These random examples show that tampering with engine cooling is a subject that requires careful consideration. Perhaps one day the oil companies will produce a super multigrade oil that cuts friction to a minimum throughout the temperature range. But even if such an oil were produced, it might be more costly to use than a system that raises the coolant and oil temperatures to the optimum figure in a few minutes and thereafter maintains the temperatures constant.
There are also benefits to be derived •from using separate cooling systems for the cylinder head and cylinder barrels of petrol engines. It is impossible to over-cool the cylinder head of a petrol engine, and rapid dissipation of heat from the combustion chamber gives improved burning, but a low barrel temperature increases friction.
In the meantime, some operators and their drivers will continue to blank-off their radiators with old newspaper and bits of tin. And some vehicles will continue to grind to a steamy, unscheduled stop in cold weather.