Is there any hard evidence that washing your car is better for the finish than not washing your car?

February 21, 2011 8:01 AM

Is there any hard evidence that washing your car is better for the finish than not washing your car? Isn't washing hard on the finish? Wouldn't a coat of dust protect the surface from sun damage? I think you can see where I'm coming from here.
posted by markcmyers to grab bag (31 answers total)

It depends on the climate and what's in the dust, to be honest. Washing your car should include the occasional wax and possible protectant application. If you're living in an area with any sort of acidic rain, possibly corrosive dust, or (and this one is the killer) salted roads in the winter, then the stuff that is building up on your car is going to be harder on your car than water and soap, by far.
posted by mikeh at 8:03 AM on February 21, 2011

The coat of dust and dirt abrades and erodes the protective paint/clearcoat, eventually leading to possible rust. Think sandpaper.
posted by Thorzdad at 8:05 AM on February 21, 2011

Anecdata: I haven't washed my car in six years. I live in North Carolina. It looks like anyone else's car - cleanish, normal paint job, etc.
posted by something something at 8:08 AM on February 21, 2011

markcmyers: "Wouldn't a coat of dust protect the surface from sun damage? I think you can see where I'm coming from here."

I don't have hard evidence (try google scholar?), but one theory is that road salt, that gets on your car, is corrosive. That's gonna trump UV rays by a mile, I'd say.
posted by pwnguin at 8:08 AM on February 21, 2011 [1 favorite]

I think with modern paint jobs the difference is not phenomenal either way, but as the not-so-proud owner of a 2007 dark blue Honda that spent its formative years in Florida (according to CARFAX) that shows a lot of evidence of not ever being waxed and bird poop being left to bake on the finish basically forever, I'd say wash the car if you care about the car's finish, and wax it at least annually with a UV resistant wax.

Also, if you never wash the car, you spend your life in a dirty car, which doesn't look good. So what difference does it make if there's a great paint job under that crap?

TL;DR - if you don't care about appearance and don't live where they salt the roads, go ahead and never wash it - something else will break before the fenders rust off.
posted by randomkeystrike at 8:12 AM on February 21, 2011

Doesn't washing shorten the life of the wax and protectant that act as a barrier against corrosion? Wouldn't you be better off adding a few coats of wax for extra protection and then not washing the car?
posted by markcmyers at 8:12 AM on February 21, 2011

It occurs to me that Consumer Reports is the most likely to have done the research you want. So here's their tips: Do's and don'ts of washing your car.
posted by pwnguin at 8:25 AM on February 21, 2011 [2 favorites]

sn't washing hard on the finish?

Shitty washing is very hard on the finish - badly maintained automatic brush style car washes are the worst offenders. If you wash a car with plenty of water (rinse well before any scrubbing), you minimise the damage done during washing. Obviously hand (ie gentle) washing is better than machine/pressure washing. Pressure rinsing is fine, though.

Wouldn't you be better off adding a few coats of wax for extra protection and then not washing the car?

The issue with a dirty car is that any road dirt that chemically attacks paint or metal (salt, anything else nasty) will be held against the paint for long periods, maximising how much damage it can do. Regularly removing this layer of dirt gives the paint less time during which it is being attacked. The best example of this is winter driven cars that get a lot of road salt caked into the wheelarches or (particularly in trucks) under/inside the running boards or rear bumpers. If the cars are not regularly washed, these areas rot out pretty damn quickly. This is, obviously, an extreme case but the principle stands.

In addition, driving through rain with a dirty car can cause damage to the paint. If you have lots of dust particles (which are predominately tiny bits of rock, don't forget) then you get a very gentle bead blasting equivalent - water picks up the dirt particles on the car and drags them across the paint surface. It's very gentle and will take a long time to be noticeable, but it is definitely wearing away the lacquer coating.

Abrasion to the lacquer coating is often what helps cause paint fade - as soon as the clear over-coat is gone, the paint itself is not very good at resisting wear or tarnishing.

The best protection for paint is the wax - it gives the surface a shiny and smooth surface that resists dirt build up. This dirt build up will attack the wax just as much as the paint underneath, so keeping it clean helps the wax last longer too. Also, you can only reapply wax to a clean car or you'll gouge great scratches into the paint. So part of the way that wax protects the paint is to stop dirt build up - so if you let it get dirty, you're reducing the helpful part of the wax's advantages.

Also, your car looks shit.
posted by Brockles at 8:32 AM on February 21, 2011 [3 favorites]

Sorry, but you pro-washing folks are just saying what everyone says, just handing down received wisdom. No one has pointed me to a scintilla of hard evidence. Even Consumer Reports makes all the same assertions without testing. I think we may have an urban myth here.
posted by markcmyers at 8:39 AM on February 21, 2011 [1 favorite]

If you want to argue with people, take this to metatalk.
posted by bitdamaged at 8:43 AM on February 21, 2011 [17 favorites]

Markcmyers, just because you're not getting the answers you want doesn't mean the rest is an "urban myth".

Seriously, don't wash your car if you don't want to, but, for example, you're going to have a very very hard time proving that rock salt shouldn't be washed off one's car.
posted by lydhre at 8:45 AM on February 21, 2011 [5 favorites]

Not hard evidence, but anecdotal: my husband's parents gave me one of their old cars a few years back. They live in the mountains of SW Virginia, which get somewhat more snow than the surrounding valley (hence salting), and they never wash their cars. I had the car maybe two months before I started sliding through stop signs, and when I took it in for repairs, the mechanics discovered a large layer of salt and crud on the undercarriage. Worse, they found nearly completely rusted-out brake lines. I was a very broke student at the time, and the damage cost $700 to repair.

I wash my cars pretty frequently these days.
posted by timetoevolve at 8:49 AM on February 21, 2011

I have lived in Hawaii and in New England. Cars that don't get washed very often rust faster. Salt and sand do terrible things to car finishes, as does bird poop. More coats of wax will give some additional protection, but you're still going to have to wash the car before you wax it, because rubbing the wax on when the car is dirty will scratch the shit out of the finish.
posted by rtha at 8:51 AM on February 21, 2011

Every single person I know who doesn't wash their car, or rarely (2x per year) washes their car, has oxidization problems, peeling paint, paint swirls, totally gummed on random crap, etc. etc. And when they do wash their car, it's pretty laughable as to a wash's efficiacy. Certainly, there could be an inverse correlation between the state of someone's vehicle, and the type of person who doesn't wash their car but I can't see how this would cause someone's paint to oxidize more than others.

I can't believe there's no hard science out there on this. It would be relatively simple to do an experiment (though time consuming) to a car part left outside in the elements for a year with only 1/2 being washed....
posted by Debaser626 at 8:51 AM on February 21, 2011

If you want to argue with people, take this to metatalk. Is it arguing to point out that people aren't really addressing my question, in which I ask for hard evidence? Is this arguing? Am I going to be voted off the island for trying to focus people on what I'm actually asking?
posted by markcmyers at 8:54 AM on February 21, 2011

Caveat: I'm basing this on my experience in California.

I have no studies to use, but consider the following observations:

1) If you look at old cars (say, 10 years plus) the paint typically looks to be in one of two conditions:
a) fine, and b) peeling off the roof/hood/ top surfaces.

I'm going to concede that "fine" can also include "lots and lots of swirl marks" which are generally considered to be the scratches you get from doing a half-assed job of washing the car.

I'm going to speculate that the cause of paint peeling on the top but not the sides of the car is due to more direct sun exposure.

So, you've got two primary problems that occur in car finishes over the years. The fist is swirl marks, which seems to be caused by washing. The second is caused by sun exposure.

Let's consider some other scenarios. There are plenty of other painted things in the world. Houses, for instance. Houses are painted with a different sort of paint, and the finish you want on a house is different from a car. But houses get cleaned essentially never, and this doesn't seem to harm the paint at all.

Or consider roadsigns. They're painted (with reflective paint) and never washed, and the only problem you tend to see in them is fading, presumably due to the sun.

Also, dirt on your paint is potentially abrasive like sandpaper, yes, but only if it's moving relative to the paint. If it's stationary, it doesn't do much damage. Once your car is caked with dirt, that dirt moves very little.

We all know plenty of people with cars. Some who are obsessive about cleaning them and some who never do. Has anyone ever observed obvious differences in the finish of cars owned by people in these different groups? I haven't noticed it.

Challenge: I would love to see someone post examples of a "damaged" finish on a car that is neither swirl marks nor sun damage, (or mechanical damage, i.e., scratching) and then summarize how that damage got there, and how it could have been prevented with cleaning. I expect someone will want to bring up bird poop or tree sap, but in my experience, these always seem to wash off when you try, meaning they don't leave any permanent damage behind.

I offer my own car as a test mule here if someone can come up with a test. Want me to tape a piece of sandpaper to my roof and leave it there for a month? I would do non-ridiculous things to try this out (I'm not going to pour paint stripper on it or anything).
posted by tylerkaraszewski at 8:57 AM on February 21, 2011 [2 favorites]

If you are in an area near the ocean or in an area that uses road salt in the winter or an area in which there are natural salts in the dust like Utah then you are better off washing the car than not washing if you want to keep it's resale value. Salty dust in a dry climate will not effect the finish as much as brine-laden air but washing and protecting the car properly will not damage the finish. The proper washing of a car can make a difference than doing it improperly which is why brushless automatic car washes are so popular.

If, OTOH, you don't care about resale value or damage to your clothes from brushing against a dirty car then your car will last approximately as long with or without washing. Give or take depending on the factors mentioned above. There is no hard and fast rule that anyone can make independent of climate. The fact is that the finish is the most protected area of your vehicle compared with the underbody. While your finish may be fine it doesn't make sense to avoid washing to save your finish when your door bottoms and under-carriage will be destroyed much sooner.
posted by JJ86 at 9:00 AM on February 21, 2011

Hard evidence of very small sample: I have a 18 year old blue volvo that I purchased about 7 years ago. I have taken it to the car wash exactly two times in the 7 years I have owned it, and never hand washed other than those two trips to the car wash. There is an identical 1993 blue volvo in my neighborhood. When I purchased my car, our cars looked exactly alike. Both are on the street (not garaged) year round. They wash their car. Their car looks shiny and much prettier than mine. The paint looks great. Mine looks dull and faded. Even when I do clean off a patch (like if there was birdpoop or something on it) once the water dries it goes back to looking faded and old instead of clean and free of dust.
Every time I see the other volvo I tell myself to wash my car, it is that noticeable.
posted by 8dot3 at 9:06 AM on February 21, 2011

Is it arguing to point out that people aren't really addressing my question, in which I ask for hard evidence? Is this arguing? Am I going to be voted off the island for trying to focus people on what I'm actually asking?

Your tone is noticeably more confrontational than is usually considered appropriate. These people are offering you free advice as part of the overall helpful community spirit.

Also note your question is vague, which might have contributed to your perception people weren't answering your question. Where are you located and what is the climate there? There are several different ways to wash a car - are you interested in opinions that distinguish between them? What kind of driving do you do? Are you just talking about winter washing or washing at any time?

That said, I wash our cars several times (at a brushless place that includes an underbody wash) over the course of the winter, and my older car (15 years old) has significantly less rust than most other examples of models its age that I see. Leaving road salt on a car, particularly during thaws when the snow and ice is liquid and seeps into cracks, is really bad. Getting the salt off and putting some kind of layer of new protective wax (even the less-effective kind from a self-serve car wash) helps.

If you live in a place that doesn't use salt on roads in the winter, winter cleaning might not matter as much.
posted by aught at 9:14 AM on February 21, 2011 [2 favorites]

Ask a scientist does confirm that salt, by itself, will not harm your car's paint--however, a combination of factors, like sun, nicks and salt all together will. Also, you need the coating of wax to help shield your car from sun damage.
posted by misha at 9:15 AM on February 21, 2011

I don't know about the finish, and so this might not be answering your question as specified, but Ford recalled more than 425,000 minivans sold between 1999 and 2003 this winter, specifically in states that salt the roads. Why? In the presence of salt, the subframe brackets and mounts on these vans were corroding to the point where the rear axles vehicles would sometimes actually separate from the frame and/or themselves corrode and break.

Now, obviously these pieces of the frame in these cars hadn't been designed properly to withstand salt corrosion—hence the recall. But even the metal on normal cars will corrode when exposed to enough salt/saltwater. There's a reason why you're not supposed to resell normal cars that have been submerged in saltwater for any period of time. And the reason people are able to get away with scams that do attempt to resell those cars is that often, you can't tell from the car's finish/paint job that the frame has been damaged by salt corrosion.

So sure, you may be able to get away with not washing your car for a long time, and your car may still look great on the outside after you do wash it—but it may also begin to develop problems and/or collapse in on itself at some point from rust damage.
posted by limeonaire at 9:23 AM on February 21, 2011

If you never wash your car, what's the point of protecting the finish? ("Hey, it's great, even if you can never see it under all that filth.")
posted by J. Wilson at 9:26 AM on February 21, 2011

If you never wash your car, what's the point of protecting the finish? ("Hey, it's great, even if you can never see it under all that filth." I'm thinking of resale value. The next owner will want a spiffy-looking car. When I put the car up for sale, then, of course, I would wash it.
posted by markcmyers at 9:30 AM on February 21, 2011

I had a Toyota for 21 years. Never washed it except when I sold it. The finish looked like new except for rock dings on the front. Do what makes you happy. Your car doesn't care.
posted by JackFlash at 9:34 AM on February 21, 2011 [1 favorite]

If you're interested in a review of the literature, they do exist. You should be able to use that as a springboard to the research you want, but it may be pricey if you're not attached to a research library.
posted by pwnguin at 9:41 AM on February 21, 2011

you pro-washing folks are just saying what everyone says, just handing down received wisdom. No one has pointed me to a scintilla of hard evidence. Even Consumer Reports makes all the same assertions without testing. I think we may have an urban myth here.

I don't think anyone has felt the need to do any major testing on something that has evolved as knowledge based on many decades of car paint usage and maintenance. Cars that are looked after and washed regularly always look better than cars that are not. Grandpas that are still driving their car from 30 years ago that look immaculate are always the examples that have been washed every week and kept in a garage because everyone knows that dirt damages paint - either chemically or by attrition.

There's not really much need to research into whether it's true when all the founding experience was achieved well before the realms of internet pedantry and insistence on searchable pdf's on precise paint degradation numbers.

The dirt on your car will grind away (on a small level) the surface of the paint. This is a very small example of erosion - this process should be familiar to you. The action of rain and wind (through driving) will affect the rate of erosion. Dirt on your car will damage it in exactly the same way, on a much smaller scale, as coastlines and terrain is formed. It's exactly the same fundamental process. It hardly needs an independent survey just because the erosion is happening on paint. In addition, there may be a chemical element depending on what is in the dirt.

Part of the reason for a lack of study on car paint is perhaps because it's pretty damn obvious and people have known about this since roughly the beginning of paint usage on cars. I know you don't want to wash your car and/or win an argument, but there is no protection to be gained by a layer of fine sand on something - it will damage it.
posted by Brockles at 9:47 AM on February 21, 2011 [1 favorite]

The dirt that gets onto a car is not inert. Bird poop, tree sap, road tar, etc., all change as they are sitting there. Sap that will wash away after a week or so will harden into shellac after a longer amount of time. Bird poop has acids and things that eat into the paint. Dust may be acid or alkaline and/or turn into a concrete-like substance. When the car does get wet, how does it dry? Does it sheet away, or does it sort of just slowly evaporate? If it does the latter, that greatly extends the amount of time the water is seeping and oozing into the microscopic pores of the paint, softening it and delaminating it. When it eventually does dry, the grit that is left behind is deeper into these microscopic pores.

OK, the stuff prevents the sun's damaging rays from hitting the paint. How does it do that? The paint protects itself by reflecting most of it, and absorbing the rest in a controlled manner. But the gunk mostly absorbs it. Which heats it up, which furthers along any chemical reactions going on, and also creates a tiny hot spot that softens the paint and lets the grit down into the paint.

You can prove it yourself: what happens to the windshield in the area where the wipers don't reach? On an unwashed car, a layer of stuff builds up, and sometimes even etches into the "finish" of the glass so you can never get it clean.

You can prove it by looking at anything exposed to the elements- things which are routinely washed are in better shape than things which aren't.

You can also prove it by looking at any car you can find. There are NONE whose paint has worn down from excess washing.

Look where rust starts on cars. It happens in places where there are chips that damage the paint. But it also happens in places like the bottoms of doors, edges of trim, that little fender area between the wheel and the door. Why? Because gunk has built up in those areas that let them remain wet longer than the areas in the wide open. Twigs and leaves block the holes that allow the body to drain and the water festers.
posted by gjc at 9:51 AM on February 21, 2011

When I was a kid, I drew my name in the dust on the trunk of my mom's car. Three years later, when she sold that car, you could still faintly see my name etched into the paint job by the abrasive dust. My mom was so pissed. So, you may not have 8 year olds grinding dust into your finish but I make a connection between dust and damage to a shiny paint job.
posted by Foam Pants at 10:07 AM on February 21, 2011 [1 favorite]

I can also tell you, anecdotally, that I know someone who hasn't washed their car as much as they should've this winter, and you can now see a little ring of rust on the paint around the edge of the lock on their trunk. That's part of the finish, and it's definitely been damaged this winter. So even if the paint itself doesn't wear down, it can be stained from rusting metal underneath/near it.
posted by limeonaire at 10:23 AM on February 21, 2011

I had a white car which I never washed. It was an ancient Subaru wagon on its last legs, so who cared?

When I finally washed it in order to get the best trade-in value, I learned the answer to that question. The dirt, bird droppings, encrusted road filth on the bottom rocker panels, and moss stains? All of them had become permanent. The only way that car was going to be white again is if I had paid to have it stripped and re-painted.

Even if you give your car a nice waxing and don't wash it, the environment will slowly eat away at the wax. And once it gets through the wax, it will start staining and etching the car underneath.

If your car only ever gets "dusty," then more power to ya. I probably wouldn't wash a car that's just "dusty." Like if it had been sitting in a garage all year, and the dust gradually settled? Meh, that's probably harmless.

But if it has road grime (a combination paste of tar, spilled motor oil, drops of gasoline, de-icing compounds, and god knows what kicked up from the pavement) or spends any time exposed to the elements, then yeah, it's good to wash it every once in a while.
posted by ErikaB at 1:38 PM on February 21, 2011

If the dust and grime on it is both completely non-abrasive and absolutely chemically neutral -- say, if it's composed entirely of Teflon microspheres -- then it probably makes no difference. But if it's abrasive at all, then just the act of driving will agitate the abrasive particles against the paint, damaging it. And if it's acidic or basic, or if you live in an area where they ever salt the roads, then even stock-still, the stuff is damaging your finish.

No, I don't have links to a scientific paper; if you want hard evidence that agitating abrasive particles is damaging, rub sandpaper on your face.
posted by KathrynT at 6:05 PM on February 21, 2011