The oil in the engine ensures optimal lubrication when the engine reaches the operating temperature. If this temperature is not reached, the oil remains too viscous, which increases friction resistance and additionally loads the engine. For example, if the thermostat of the cooling system is defective and the coolant remains at a temperature significantly below the optimal one, such as below 60°C, the engine will operate inefficiently, which leads to higher fuel consumption.
Black-coloured smoke emitted through the exhaust indicates an excessive fuel consumption. This can be the consequence of injector failure (clogging of the spray holes), sticking of the injector needle, leakage of the injector needle, etc.
Operating with interruptions can be caused by faulty injectors or by a fuel mixture that is too rich, thus burning more fuel compared to normal operation. Therefore, engine operation with interruptions leads to increased fuel consumption.
The situations in all three answers lead to increased fuel consumption.
The correct answer is: A, B and C
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