Autospeed quoted a paper written by Volvo’s Dr Simone Sebben (SAE paper 2004-01-1307) about an un-named vehicle with a total drag coefficient of 0.29.
The list of parts of the car and their contribution to total drag show the cooling system as the worst offender:
Parts ... Percentage of Total Drag
Cooling package (including radiator, intercooler, oil cooler, etc) ... 33.4%
Exterior ... 31.7%
Front wheels ... 13.1%
Rear wheels ... 6.9%
Floor ... 6.9%
Rear Axle ... 3.1%
Engine ... 3.1%
Front Suspension ... 1.4%
Exhaust ... 0.7%
Source:
Modifying Under-Car Airflow, Part 1
The only red flag in that data to my eyes is the label in the graph: "including radiator, intercooler, oil cooler, etc". If the vehicle in question actually has all those components, it likely has more cooling system drag than our small cars, which only have radiators.