trainmaster_1 wrote:Those carbody mesh screens on CP's 5700 series SD40-2's are used to keep the prime mover and carbody cool under high stress operating conditions, since some but not all units are assigned to snow plow service on the CPR, which is why they have the carbody mesh screens.
I am not sure about cooling the prime mover. The SD 40 long hood was designed to have positive pressure created by the exhaust of the cooling air of the traction generator exiting through the D-14 to restrict dirt from the entering the long hood. The extra screening added to the inertal filters (of the choo choo in the pic) will restrict this air flow further reducing the cooling air to the traction motors and traction generator (not to mention starving the air hungry turbo). This may be a quasi snow operation. The standard snow operation package of the late 70's was to modify the #1 cooling fan to (through shutter operation controlled by a snow operation switch in the cab, usually located near the isolation selector switch) redirect warm air through the long hood and through the bulkhead (also shutter controlled) between the engine compartment & generator compartment. A few of the Soo or Alaska units had shutters on the inertials too.
If the unit in the picture is modified to move air through the long hood for snow operation I would be concerned that the oil lines for the load regulator would not like the cold air and would cause the governor to hunt because of sluggish operation of the load regulator due to cold oil. The way to fix that is to find a way to heat the load regulator supply lines from the governor.
