Does a car wash increase mileage?
 

Does a car wash increase fuel mileage? If so, how much? Does anyone have data - or data sources - on this?

On a similar note - I've heard something about a layer of film to apply to your car after a wash to protect from minor dirt, water, etc. to reduce the needs for car washes in the future. Different from a full wax, but somewhere in between. Thoughts?

Can't see a car wash making much difference. I guess you are thinking it might be more aerodynamic after a wash or even a bit lighter but I reckon the differences would be so tiny as to be incapable of measurement.

I remember seeing a study a couple years ago that showed that freshly waxed cars had slightly less aerodynamic drag, so in a way a clean car is more efficient.

Might save you a dollar in fuel, but it would cost more than that to wash it every month.

A car that is kept clean generally lasts longer and has a higher resale value as well.

https://www.youtube.com/watch?v=NNKMOqpfM20

The user split that episode up into 4 parts, so check them all out to see the whole thing, however, you can skip through the "hangover" tests. Pretty neat episode overall though.

I think that the Mythbusters did this test a while back. I also remembered they dimpled a car body like a golf ball and got a measurable increase as well. Might be able to find that information online somewhere.

Or just look at my post... Lol.

I think that myth has been busted for a while. If it were to make a difference with your MPG you wouldn't even notice it.

Think of it like tire pressure; its one of the most important things to check for safety/durability, but the 3% decrease in mileage is almost unnoticeable when you run under-inflated tires.

Way back a long time ago, there was an article about this flight in an Air Force publication. The story had it that one of the C-130 folks noticed in the flight manual that the range of the C-130 exceeded a then-current world record. He brought that to the attention of the Powers That Be. As part of the preparations for the flight there was a base picnic, during which many folks took great pains to wash and wax the airplane in hopes it would help. The quote from Wikipedia follows.

World's longest turboprop aircraft distance record[edit]

On 20 February 1972, Lieutenant Colonel Edgar Allison, USAF, and his flight crew set a recognized turboprop aircraft class record of 8,732.09 miles (14,052.94 km) for a great circle distance without landing. The USAF Lockheed HC-130H was flown from Ching Chuan Kang Air Base, Republic of China (Taiwan), to Scott AFB, Illinois in the United States. As of 2013, this record still stands more than 40 years later.

I wonder just how they did that. Did they shut down any engines? I doubt it as AF C-130 crews are really loathe to shut down engines in flight like Navy P-3 crews regularly did/do on long patrol flights. I rarely ever saw a C-130 taxi out to the take-off runway on only 2 engines like a P-3 crew would for a long patrol. AF crews are probably not co-ordinated enough to taxi and start engines at the same time. In fact, I would expect a P-3 could give the C-130 a go at that record since it has basically the same engines as a 130 but has a lot skinnier fuselage. P-3 may have smaller fuel tanks though because it sure has stubbier wings. I know the P-3 holds the record for speed for a 4-engine turboprop aircraft.

In any case, I wouldn't expect the Navy to try to best the AF on that record flight. The AF tends to be more of a show-off service while the Navy more quietly goes about its business. Let the flame war begin.

The C-130 was designed to be able to shut down one engine during cruise in order to extend range. The HC-130 was a variant which had a cargo-bay mounted (removable) fuel tank as a standard fitting, which could be used either to transport fuel, extend the range of the base airplane, or refuel other aircraft in flight (helicopters, for example). Since that auxiliary fuel tank was a standard piece of equipment it was legal to use it for setting records.

A story came out of Turkey about a C-130. During initial startup, one engine would not start. It was determined that the problem was not the engine, but the starter. The AF crew got onto the runway with three running engines, got the airplane going fast enough to air-start the fourth engine, and completed the day's flights by simply leaving that engine running instead of shutting all four off and using the APU on the ground. It took a little more care for the ground crews to avoid the propeller.

In a 2007 article from "Hot Rod" magazine " meticulously polish the vehicle's surface" is mentioned under "Aero Tricks You Can Use". But I still have found no reported ( hard facts ) backing up that a washed/waxed car gets better mpg's.

Has anyone ever tested this with a scan-gauge, ultra-gauge or similar ? All conditions being the same (as close as possible) except the wash/wax for the 2nd test. If the weather ever warms up I plan to give it a go.

I can see how a film of dirt will increase air drag. I can't see how it would have a measurable effect on fuel economy in the typical car though.

Ditto that, you must be talking micro millograms of fuel if any. Somthing as small as a sneeze at the wheel could ruin your results!

It might make a different on something like the limited run ultra efficient VW. Then you might just keep it cleaned and waxed because you just dropped 6 figures for it though.

For those of us in econo boxes, tweaking the aerodynamics with grill blocks and belly pans will give more gains than keeping the car clean.

Thanks for all the shares guys. Guess the lesson is to poke little dimples in my car's body! :)

Glad to hear the consensus is that the impact is minimal, though. Potentially saves some money on car washes I may have wanted otherwise.