Lubricating oil viscosity in an operating diesel engine can be reduced by（）

A.engine power losses
B.smoking due to unburned fuel
C.high exhaust temperature readings
D.all of the above

A.incorrect replacement of barrels and plungers of jerk pumps
B.overheating of the nozzle orifices
C.cracked pump housings
D.dirt in the fuel

A.tachometer
B.pyrometer
C.dynamometer
D.calorimeter