单项选择题
A.The coolant temperature must be maintained at 180℃
B.The thermostatic bypass valves must be manually opened before the engine is started
C.The pressure cap must be removed while the engine is secured
D.Electrical power to the heater must be secured before the cooling system is drained
单项选择题 Which of the following statements is true regarding the installation of piston rings on two-stroke/cycle, diesel engines as compared to four-stroke/cycle, diesel engines?（）
单项选择题 If a crankcase explosion occurs in a diesel engine, which of the listed actions should be taken?（）
单项选择题 A substance found in residual fuels which tends to cause exhaust valve corrosion and grooving, is（）