How much do grill openings effect Cd?

[EcoCivic]

Ok, so I duct taped over the upper grill on my 2005 Civic but left the bottom open since that is where I put my transmission oil cooling radiator, and I don't want to overheat my transmission. I will reply with an update soon.

[Xist]

Also, while many newer cars have huge grills, much of that is fake. People want to believe they have a mouth-breathing monster, but there is no reason for it.

[aerohead]

Originally Posted by EcoCivic

I have heard that between 1/4 and 1/3 of the aerodynamic drag on a car is from the cooling openings. That sounds like a LOT of the drag on a car is from air going through the radiator, and I have a hard time believing that cooling causes 1/4 to 1/3 of the aerodynamic drag on a car. If that were the case, wouldn't I have lost a measurable amount of gas mileage when the front grill fell off my 2005 Civic? I was sure that having a big hole in the front of my car would hurt highway mileage at least a little, but the effect on gas mileage even at 60-70 MPH on the highway was not measurable. Also, if drag from cooling was so significant, why do people only get 1-3 percent MPG improvements, presumably mostly from faster warm up, from a full grill block? nPlease help me understand!

I've never seen more than 16% of overall drag reported as a worse-case scenario.
2% is credited to good racing design.
1976 Ford Lameller Grille was associated with a 12% drag reduction
1938 Adler-Jaray saw 15.78% with a 100% block
2013 Dodge Dart,active shutters 3-to-5%
1982 Pontiac Trans AM bottom-breather 3.08%
1967 Corvette EV with 100% block 6.5%
1986 FIAT R&D 100% block 10.2%
1978 Chevette 4-DR with 100% block 7.56%
2009 Audi A2 100% block 9.7%
2007 Ford Fusion 999 hybrid LSR 100% block 7.35%
By the old metric,you'd see a 1% improvement in HWY mpg for every 2% drag reduction,based only upon the original mpg.