Q. Should I hand wash or use an automatic car wash?
A. While many people believe that hand washing is safer to a vehicle's finish than automatic washing, this is not necessarily true. A few years ago, The Technological University of Munich did a study for Mercedes Benz to discover which method of washing was safer for the finish of a vehicle. A few years later, the University of Texas was commissioned by the International Car Wash Association to conduct a similar test. The results were quite startling. It was found that hand washing a car 26 times and washing a car 26 times at an automatic cloth car wash, the surface of the hand washed vehicle showed damage. This was determined by taking microscopic pictures of the paint finish. When enlarged, these photos revealed deep and numerous scratches in the paint of the hand washed vehicle.
Why did this happen? It was determined that each time the hand wash sponge or mit is placed on the surface of the car, it continually picks up girt in the fibers that are not rinsed out. This grit acts like a very fine sandpaper putting scratches in the paint.
In an automatic car wash however, the car is constantly flooded with water and shampoo. This forms a protective layer between the washing material and the paint surface which washes away girt and dirt before it can damage the finish.
Additionally, most people who wash their cars at home don't realize where the contaminated water goes, or how much is wasted. Home car washing releases contaminated water directly into the environment, or into storm drains intended just for rainwater. This causes pollution in our rivers, lakes and streams. Also engineering studies show that a 5/8" hose running at 50 pounds per square inch uses 10 gallons of water per minute! As many as 100 gallons of water could be used in a ten-minute home car wash – most of it wasted.
And the opposing view from another website
A 'Touch less' or Tunnel car wash must be a safe way to clean your vehicle
Most so called 'Touch less' car washes today use a low pH acid as a first step, an alkaline to neutralize it and then high pressure water to wash cars. Hand washing is MUCH preferred, do not use an automated car wash period, touch less or not, there are a variety of reasons: Local by-laws require car washes to re-claim or recycle water. This means they have two choices.
They can collect the water in tanks and pay to truck it away to a recycling centre or they can filter and then recycle the water (dependant on how often the filters are cleaned /changed) will affect how much dirt content there is. Recycled meaning re-use the same water, which may include any road dirt/grit that is not filtered out is used to high-pressure (1,000PSI) wash your vehicle (somewhat similar to sandblasting) the final rinse is usually twice-filtered re-cycled water, this is to give the appearance of a clean surface on the vehicle.
To help clean the recycled water they use a chemical like Presidium Orthophosphate (TSP) and have the chemical formula Na3PO4. It is a highly water-soluble ionic salt. Solutions of it dissolved in water have a high alkaline pH; this does a great job stripping your wax / sealant. TSP is generally not good for cleaning vehicles because it can corrode metal.
Covered leather upholstery requires regular conditioning
As the top surface has polyurethane finish over pigmented finished leather, creams, oils or conditioners should not be used. Reminder; you are dealing with the finished surface coating and not with the leather itself.
As I live in minnesota and do snow plowing my truck is often transformed into looking like a salt lick. I try to use the self serve washes but often time and locations become an issues so it's a toss up between touchless wash or waiting a week to be able to self serve wash it. Positives and negatives for both methods.
