Highway overheat
I design and build refrigeration equipment and have looked at many radiator/electric fan combinations and thought the shrouds look like they would do a good job of getting enough air through at idle but would tend to block the air-flow through the portions of the radiator that are not directly in line with the fan(s).
OE shrouds have sufficient space between the fan and the back of the radiator coil bundle. This space combined with a nice shape/taper that permits air to pass through the full radiator surface then be routed to the fan makes the OE shroud work properly.
|