why do you guys need a clean engine room? do you live in it? do you eat in it? leave it alone - if its really dirty - wash it like the manufacturer wants you to wash it, when the engine casings are cold and using proper cleaning agents and brushes taking proper precautions, then coating the plastic parts with protectant, metal parts with their protectant and painted areas with wax. Otherwise leave it dirty. Your feeble attempt of caustic detergent, water and diesel fuel oil will make it worse as it wont clean but rather distribute the grime everywhere.
Why do you guys think that the car is cattle? and needs to be washed inside out with 200 gallons of water at a stupid lift service station..