So I finally asked my friend who (machine) washes their car every week or two... why do you wash it so often? The reply was that a clean car gets better gas mileage than a dirty car. Huh? Unless you have chunks of mud the size of cinder blocks clinging to the sides of your car, I cannot imagine how a little road dirt can impact MPG. This has got to be a myth, right?
During WWII, some fighter pilots had their aircraft waxed and polished, they claimed that improved performance by between 5 and 10 mph, that may be the origion of the clean car myth.
Mythbusters did something along these lines. However, them being them... obviously exaggerated the tests to really display the aerodynamic improvements from a clean car, to a dirty car... (which there was a difference, however fairly minuscule from what i remember... nonetheless, there was an improvement) But the most surprising part of the test was that they went into the "golf ball effect".. where they covered a car in golf-ball like dimples.. The results were utterly surprising.
It's more of an attitude thing than a direct results thing... You can do many things to improve your MPG that are so small of a change that they aren't really measurable. But if do 50 of 'em they may all eventually add up to measurable fuel savings over time. The biggest influence on MPG of course is driving conditions and driving ability. There are some sweet spots at certain speeds under certain conditions where Prius does best at MPG and the more you geek out on every aspect of MPG improvement, the more likely you'll make the most use of it. Of course to do that you're gonna need more instruments so you have a better sense of RPM, throttle position, etc.
Yes, once you get up to fighter pilot speeds, even way back then, the amount of air pressure involved could have that kind of slight 5 - 10 mph difference, which is pretty much unmeasurable in a car at freeway speed.
I assure you that my attitude towards driving is no different when my car is sparkling clean or covered in dust. I already do everything I can to increase MPG - short of becoming a road hazard, that is. I just don't see where a slight film of dust or build up or normal dirt could impact the gas mileage, especially not on this car... certainly not in any measurable sense, maybe over the whole lifetime of the car.
Your neighbor is messing with you. But, a clean car is a happy car. At least this driver is much happier. Dan
I agree with other posters that a clean versus dirty car will make only a miniscule difference in fuel mileage (some improvement in laminar air flow over the sheet metal). However, there is an indescribable mental stimuli that you get in approaching and driving away in a spit polished car. It's like walking around in a pair of dirty old shoes compared to having polished ones. To some it makes no difference, to others.......................
Its not psychological. When the car is freshly washed, water that is sprayed everywhere gets in those little areas and acts as a lubricant...thus making the car run better. Imagine soaking your car in oil and then taking it for a ride... water does the same thing. That's why you never buy a vehicle when its raining, and that's why it is good to wash your car just before a test drive when you're selling it.
