Fuel Economy Tip - Wash and Wax?
June 13th, 2006 | by Brian Carr |I wish I knew for certain that today’s tip actually does help you get better gas mileage, but even if it doesn’t, you’ll have the nicest looking car in the neighborhood.
Regularly wash and wax your vehicle.
If this idea actually works, I wish I could take credit for it (if it turns out to be a scam, you didn’t get the idea from me). While searching other gas saving sites, I came across a tip that claims if you wash and wax your car, you can improve your gas mileage by up to 7%, which based on today’s prices would be about $.27 per gallon.
Not too shabby.
The basic idea behind it is, after washing and waxing your car, the surface of the vehicle is much more likely to be nice and smooth, therefore, it should be more aerodynamic than when you have lots of bug guts smeared all over.
It looks like a sound theory, but I don’t know if simply cleaning your car will increase your fuel economy that drastically. However, it’s worth a shot because at the very least, your car’s going to look nice.
Especially if you’re NOT kicking sweet rims.
56 Responses to “Fuel Economy Tip - Wash and Wax?”
By Anonymous on Jun 13, 2006 | Reply
7%? No way. Maybe if you have an elephant smeared on your trunk, but that’s it. Plus, the cost of wash/wax materials is going to offset that cost and make it not worth it (assuming the looks don’t matter).
By lisa on Jun 13, 2006 | Reply
That’s the most retarded thing I’ve ever heard.
By Anonymous on Jun 13, 2006 | Reply
It’s technically reducing the surface friction… I’d doubt that 7% is anywhere near the real figure, unless you had 400 pounds of dirt caked up under and on your vehicle. None the less, friction is friction and reducing any way possible helps in some way.
By Anonymous on Jun 13, 2006 | Reply
This is fairly absurd. Yes, surface friction figures into a car’s drag, but the overall shape has a far heavier influence. Perhaps this tip should have been called something to the effect of “buy a car with a low coefficient of drag.”
By Anonymous on Jun 13, 2006 | Reply
Heck, if you’re washing the car that often, you’ll spend all the money you’re “saving” on wax, soap and heating the water.
By Anonymous on Jun 13, 2006 | Reply
I don’t want to be pedantic (ok, I do), but improving your gas mileage IN NO WAY REDUCES THE COST OF THE GAS! IT reduces how much you burn to drive a particular distance at a particular speed with a particular load, yada yada yada. Assuming this is even true (which I doubt), a 7% improvement on a 35 mpg car gains you not quite 2.5 mpg. Or barely half a mile per gallon in your 8 mpg beguzzlehemoth.
If you REALLY want to improve your fuel economy, buy a fraking Vespa.
By JB on Jun 13, 2006 | Reply
A classmate of mine once worked at the local FedEx terminal washing trucks. Every night. I mentioned to him that it seemed like a waste of money just to have clean white trucks. His response was that FedEx had studied the problem, and determined that washing the trucks every night saved them millions of dollars a year in fuel costs (company-wide, of course). Of course, FedEx has many, many trucks, and they all drive many, many miles a year, so while washing your car regularly might save you some money, it’s the economies of scale that really make it pay off.
By Anonymous on Jun 14, 2006 | Reply
7% is for airliners, which go 550 mph and have no tire/road resistance. Cars would be more like .1%.
By Anonymous on Jun 14, 2006 | Reply
….until you decide to open a window.
By Anonymous on Jun 14, 2006 | Reply
Pfft. My Honda has probably 6 pounds of bird shit on it and still gets way over the EPA highway mileage. And I usually am going 75-80 mph.
By David on Jun 14, 2006 | Reply
Yep, it’s pretty unlikely for any automobile. However, weekly washing and biweekly waxing do more than reduce drag.
By washing you’re removing dust and dirt that the vehicle may suck in into the air filter, which will reduce gas mileage. Keeping your car cleaner keeps your air filter cleaner as well. This also in turn means your engine is generally taking in slightly cleaner air than if the car were dirty, keeping it cooler and more efficienct.
When you wax you decrease the friction of your cars’ surface, decreasing the amount of dust, dirt, and polen that will stick to your car, while only a miniscule amount, if you go, say 2 months without waxing or washing, the figures could definitely become noticeable.
By Nobrainer on Jun 14, 2006 | Reply
“nice and smooth” isn’t always good.
Ask a golf ball designer.
More info, aero drag accounts for only about 2.4% of total energy loss. [link]
By Nobrainer on Jun 14, 2006 | Reply
Make that 2.6% of total energy.
So cutting your aero drag by 50% (unlikely) should lead to an average 1.3% fuel mileage increase.
By Anonymous on Jun 14, 2006 | Reply
This cannot be true. I concede that when you accelerate, your car spends most of the energy on moving itself, but once you are at a steady speed, the rolling resistance is ridiculously low. You can check my own calculations (for F1 cars on a totally different topic) here. Using the same Excel sheet (corrected by the members of the thread I gave you), I find that, at 100 kmh, for every hp spent on overcoming rolling resistance you spend 10 hp (13 actually) overcoming drag.
On the Excel worksheet, I used 99 to 100 kmh (to avoid divisions by zero for kinetic energy), 2 square meters frontal area, 0.3 CV. Look at rolling resistance and drag figures. Please, take in account these are “power to the wheels” data, as the thread explains.
By Anonymous on Jun 14, 2006 | Reply
BTW, you can easily check if I am right, assuming that the equations for drag are correct (as CFD designers do…
) and measure your car rolling resistance. Simply, take it to a low speed (to minimize drag losses), let’s say 40 kmh (or 30 mph, for example) and let the car coast to a stop. Measure the distance it traveled. Your coefficient of rolling resistance is simply half the speed in kmh (20 kmh = 6 m/s) squared (36 m/s) and divided by distance. It should be around 0.01. This are the watts you spend by every kilogram your car weights and the meters it travels.
By Anonymous on Jun 14, 2006 | Reply
this is true, i have been waxing and washing my car since i was first able to drive and i believe that it is totally accurate. after a good cleaning and waxing you car feel less wind resistance and the car slices through the air better. exspecially on windy days. so quit being so fricking lazy and couch potatoed and get your fricking self out and take care of your car.
By Anonymous on Jun 14, 2006 | Reply
Wow! Glad people are reading this blog!!! Happy Birthday Brian!!!
By Anonymous on Jun 14, 2006 | Reply
Washing your car also helps it last longer by removing the crap that traps moisture (dirt and bug guts) against your car promoting rust. Less friction = better mpg. Lisa, “That’s the most retarded thing I’ve ever heard.” — you need to get an edumacation.
By Anonymous on Jun 14, 2006 | Reply
and here’s a book to prove it!
pops up
By Anonymous on Jun 14, 2006 | Reply
Ithink I once read that ups washed its planes for the same reason
By Brian Carr on Jun 14, 2006 | Reply
Good God. Who thought that the most mundane idea I’ve ever posted would get this most attention.
Keep in mind, I too am skeptical of the 7% increase in gas mileage, I just posted what the other article stated.
Also, to the person that stated that improving gas mileage does not improve the cost of gas - yes, you are right, you’re going to spend money on gas, and probably close to the same amount, but if you can get better fuel economy, you’re going to fill up less often, so that’s where the savings comes in.
By Brian Carr on Jun 14, 2006 | Reply
Just out of curiosity, how did all of you find this blog?
By Anonymous on Jun 14, 2006 | Reply
Forget waxing the car, I’m gonna smear KY Jelly all over the car and get 10% better mileage!
By Anonymous on Jun 14, 2006 | Reply
The guy who mentioned golf balls has the right idea. If the surface is perfectly smooth, air isn’t slowed at all and you end up with a larger vacuum behind the car, aka DRAG. That’s why golf balls are dimpled, to slow the surface air down so less vacuum is created, allowing the golf ball to go faster and further. Lisa said it best.
By Anonymous on Jun 14, 2006 | Reply
This post has been removed by a blog administrator.
By Anonymous on Jun 14, 2006 | Reply
A dimpled golf ball travels further than a smooth one with the same stroke. So I was wondering why race cars aren’t dimpled. Would they go faster? Would dimpled passenger cars get better mileage? I will take a nail and hammer and go try it right now. Wish me luck.
By Anonymous on Jun 14, 2006 | Reply
The golf ball example is not a valid comparison. The dimples decrease the speed required for the flow to transition from laminar to turbulent. In this transition range the pressure drag drops dramatically at first. However as you continue to increase speed the drag will eventually increase with increasing speed.
By Brian Carr on Jun 14, 2006 | Reply
That’s what I like to see.
By Anonymous on Jun 14, 2006 | Reply
i was led here by fark.com
By Brian Carr on Jun 14, 2006 | Reply
I’m not familiar with Fark.com, although I’ve heard of it. What sort of site is it?
By Anonymous on Jun 14, 2006 | Reply
Ok, the KY Jelly comment was totally inappropriate.
By Anonymous on Jun 14, 2006 | Reply
Fark.com = news and misc. things… a collection of posted links, photoshops, audio edits, etc.
Fark.com? It’s fark. :+P
By John on Jun 14, 2006 | Reply
Hah! That’s ridiculous. But I am glad that people are thinking about gas mileage.
I have a Honda Insight that I haven’t washed in the 6 months. I’ll do a test to see if it works. The fuel consumption gauge will help test out the theory (if I actually wash it today).
On the other hand, increasing the speed from 59-60 mph reduces fuel consumption by 2.65% (2 mpg - I usually get 75 mpg on the highway at 60 mph.)
-John
invisiblegold.com/about/tourdesol
Note: The numbers are from a program called “PowerCalc”. It seems to match the results I get driving.
By Anonymous on Jun 14, 2006 | Reply
YAY FARK
By Jeff on Jun 14, 2006 | Reply
It is true actually. People are misusing the government fuel consumption website. That 2.6% is removing an additional 2.6% of the 12% that goes to the wheels. Aerodynamic drag causes a 15 to 20% loss of the energy that was delivered to the wheels.
The golf ball analogy is also way way off. Golf balls travel upwards of 100 mph at times when hit. The reason golf balls are dimpled is because a sphere is an awful shape, aerodynamically. There is no vacuum, there is profile drag, or where the air separates from the surface, leaving stagnent air. The dimples create vortices along the surface, causing the boundary layer to trip to turbulent.
A car, on the other hand, is shaped more for aerodynamic purposes, and has much much less profile drag (though it still has some). I think people are taking this way out of context to. What time period are we comparing? A car that hasn’t been washed for a year vs one every other week? In that case, the actual savings might be closer to 10-15% comparatively. If you wash your car once a week and do the bi-weekly waxing, it will be significantly more efficient than a car that washes once a month or longer.
By Joe on Jun 15, 2006 | Reply
The advertising machine will love the people who read this. He said “up to 7%” and we all know that means anything between 0 and 7.
So, its most likely true because 1% is between 0 and 7.
By Kromm on Aug 24, 2006 | Reply
approximately 7% is what I have heard for turboprop and jet aircraft, even though it entirely depends on the shape and surface area of the leading edges of the aircraft. Some aircraft have more surface area on the leading edges than others in the same size class and make up for it with bigger engines or slower stall speeds so you cant actually give an exact number tho. However 7% approximate doesn’t sound ridiculous for an aircraft. The approximate wind resistance/fuel economy numbers for washing an aircraft and having sunk rivets (which is another aspect that is commonly talked about in terms of fuel economy) still differ greatly tho from plane to plane…
By Aerospace_Engineer on Aug 24, 2006 | Reply
Uhh…. Aerodynamic boundary layer is nearly the same for smooth waxed paint and bird shit covered paint.
Only coating your car in sandpaper or something to make it totally rough would actually help more, because it will help the flow field stay attached longer and cut down on skin friction drag that way…
Then again skin friction drag is orders of magnitude lower than pressure drag caused by cross sectional area.
By raoul on Aug 24, 2006 | Reply
Using this logic, stiking my hand out of the window should reduce my fuel efficiency by one half.
http://www.cruel.com
By skip on Aug 24, 2006 | Reply
no way i own a vanagon wash it why it’s like a flat box going down the road
By McBear on Aug 24, 2006 | Reply
Most of the savings will occur during highway travel when a well waxed, clean car will get better mileage. Any type of race car is clean to the point of shaving the edges of decals for extra areodynamics. All those little bumps and bird droppings and rough surfaces on the hood, windshield and roof do slow the airflow down. A cleaned car usually also includes getting crap out of the trunk which is dead weight as far as gas mileage is concerned. Wax on the paint, RainX on the windshield.
By FarkDaddy on Aug 24, 2006 | Reply
Wow. Cool blog.
My head is spinning.
————————-
By Dato on Aug 25, 2006 | Reply
I just washed my car and I now am getting over 800 mpg. Guess it really does work!
By Brian Carr on Aug 25, 2006 | Reply
Contratulations. I hope your clever wit takes you as far in life as your 800 mpg will.
By Steve on Aug 25, 2006 | Reply
Washing cars, checking tire pressure, etc is all good- while you are at it- drop the ski rack - that right there will save you 5 MPG-Easily-
By Jim O'Brien on Aug 25, 2006 | Reply
People - you’re missing the BEHAVIORAL element here. Someone who is devoted enough to wash their vehicle weekly is someone who clearly values their automobile a great deal.
As such, they will be less prone to aggressive acceleration, high speeds, and erratic driving that lead to greater fuel consumption. Basically, if they love their car enough to wash it all the farking time, they’re gonna baby it on the roads.
It’s psychological. The people that report 7% are the same ones that lovingly ease their car in and out of traffic, then wash/wax every Sunday.
By Brian Carr on Aug 25, 2006 | Reply
Interesting point. I sent an email to UPS last night because I had heard one of the reasons they wash and wax their trucks so frequently is because it helped to increase gas mileage.
By randy on Aug 25, 2006 | Reply
I call shenanigans.
Golf balls have dimples on purpose to rough up the air right over the surface - to get BETTER aerodynamic properties.
If the dirt on the vehicle weighs alot - then you might see a benefit - but you are not losing mileage to little bumps.
By Curtis Linton on Aug 25, 2006 | Reply
Anyone with enough K-Y jelly to smear on a car needs serious farking help.
By Mister Lizard on Aug 25, 2006 | Reply
Still seems highly unlikely. Give the guys at Mythbusters a call. I’d like to see them try it our on TV!
By Andrew on Aug 25, 2006 | Reply
Let’s get the MythBusters chant going!
By Bill on Aug 25, 2006 | Reply
I would love to se Mythbusters compair a clean car to a car with K-Y Jelly all over it!
By Jeremy on Mar 24, 2007 | Reply
I believe that you can see a slight improvement with a clean car. I agree with the guy that said you can tell a difference in the way the car handles on the road. Like when the wind blows accros the road the car isn’t affected as much. So this must have something to do with the drag being affected in some way. With a boat it is well known that you can get significant mpg and speed gains with a clean, waxed hull.
Also don’t forget you have the underbody of the car. This is where you can get some reduction in drag. Lots of dirt builds up here and adds to the drag of the car. Also affecting the condition of the suspension, brakes, and exhaust.
I found this blog though a google search, “top reasons to wash your car”
By Brian Carr on Mar 24, 2007 | Reply
Jeremy - Thanks for the comment, and great point about the underbody of the car. I’m sure over time plenty of crud (yes, that’s the technical term) builds up down there and adds weight/increases drag. Also, thanks for letting me know how you found this site.
By Maciej on Jun 17, 2008 | Reply
I found this site by Googling: “Does waxing improve fuel efficiency”. I’m trying to remember why I decided to google that… and the reason is I just wax buffed all the cars in the household, my ‘93 Explorer which has no paint on hood or roof and has silicone applied inside the water guides covering rust with a nice Yakima roof rack which I recently tore off by getting stuck between trees is getting a yearly average of 13.8mpg city/highway but being mostly city. I keep the sides and back… clean and waxed but I’m sure as above poster mentioned dirt and underside grime all add up. I thought, I do take the Explorer mudding alot and even though I take care of it cosmetically (not the original owner, and sun likes to bake cars here in South Florida) and probably have a couple pounds of Key Largo Limestone stuck underneath… will putting tire shine on the spare help also? The surface will be smoother but it will also be alot stickier than mud… I’m also bringing the thread from a one year halt. Did a year of wax engineering bring up the percentage to 8? Also, I notices alot of smart people on the board referring to the theory of the golfball and such.
Also to the person that stated people that wash and wax their cars are usually less prone to aggressive driving. This is wrong, people in my age group (18-30?) take great care of car cosmetics and also take great care of the car mechanically, but we do take our cars to the track either testing full potential of the motor at the drag strip or riding on bump stops taking the tight left hander at the local autocross meet. Also I’m sad to say, alot of our age group use our vehicles for “showoff” purposes which include waxing and also include car abuse by the unwise.
Of course to completely turn around that idea, a pothead will drive a lot less aggressively then a stressed, sober person fighting five o’clock traffic. Even thought the couch mobile will have windows covered in bird shit and an engine bay full of leaves and rat nests the car will get better fuel mileage then a mint washed car of a Fast and the Furious kid coming from the car wash not knowing jack, nor a devoted racer coming back from the track with melted rubber stuck inside the wheel wells, but hey, he did have a clean waxed and light car when he left right?
By Mark on Jul 28, 2008 | Reply
I believe it helps a little bit, but no where near 7%. I am one of those anal car guys and will occasionally go further and use a clay bar to pull crap off the surface. This leaves the paint in a nearly new condition. Dragging a towel across a portion that has this done vs not done, you can feel additional friction (even with bare hands), and hear the roughness from the towel. Ships have their hulls cleaned as maintenance. Of course water is much more dense than air and its effects are more pronounced.
I dont believe that just washing, in fleet applications, makes enough of a difference to offset the costs involved in labor and water.
WIll it offset the costs if its waxed and clayed as well? Probably not. Its just a nice benefit to those that are meticulous with their automobiles. Undoubtedly, 90% of the public doesnt have the mental fortitude to take care of their cars well enough to make them last at LEAST 10 years. I own a repair shop and see this on a daily basis, so no one can make me believe otherwise.