Carwash vs. Dishwash
There are seven reasons why washing cars with dishwashing detergent is dangerous to a car’s finish.
Problem #1: Water softeners
Dishwash: Companies producing dishwashing detergents assume dishes will be hand dried, therefore, dish detergents do not contain water softeners to prevent spotting.
Using dish detergent on an automobile actually increases the likelihood of water spots.
Carwash: Many carwash products contain chemicals to soften the wash water, which helps prevent water spotting upon rinsing.
Problem #2: Grease cutters
Dishwash: Dishwash detergents are generally made with surfactants that are very good at grease cutting and removal. These surfactants are likely to strip the silicones and waxes on a vehicle.
Surfactants also strip protection on any bare metal parts of the vehicle, such as the engine compartment or areas inside the doors. This will promote rusting when wash solutions find their way into these spots. In addition, any chipped spots on the paint would be susceptible to corrosion.
The end result is a dull, unprotected finish, and the possibility of corrosion in undetected places.
Carwash: Carwash detergents are made with surfactants that are gentler to the car’s surface and will not strip the car of protectants needed to maintain a glossy and safe exterior.
Problem #3: Emollients
Dishwash: Dishwashing detergents often contain cosmetic chemicals (emollients) for your hands. They keep your hands soft and prevent the cracking and drying that may occur from being immersed in water for too long.
These cosmetic ingredients may make the vehicle difficult to dry or leave it with a poor gloss finish and smeary appearance.
Carwash: Carwash detergents do not contain emollients to soften hands or provide any other cosmetic perks.
Problem #4: Surfactants
Dishwash: The surfactants in dishwash detergent may produce foam that is thicker, denser, and won’t rinse as well as traditional carwash soaps.
Because dish detergent may not completely wash away, the vehicle would sustain either bad water spotting or a smeared finish.
Carwash: Surfactants are added to give a thicker, stronger appearance to the product, since thin soap is often misconstrued as weak. However, the surfactants used in carwash products are not the same as surfactants added to dish detergent.
Problem #5: Dirt removal
Dishwash: For the most part, surfactants used in dishwash detergents are not the same as those used in a carwash. The surfactants utilized to remove food from plates are generally not the best surfactants to remove dirt from your car.
These surfactants end up leaving dirt and/or film behind, causing the home washer to work harder or wash the vehicle multiple times. Carwash: There are surfactants added to remove dirt.
Problem #6: Additives
Dishwash: Dishwash detergents do not have special additives.
Carwash: Some carwash detergents have extra benefits due to special additives not found in dishwashing detergents. For example, a small amount of high pH additive helps with dirt and road film removal and to neutralize any acid rain spots on the vehicle.
Problem # 7: Table salt
Dishwash: Sodium chloride (table salt) is commonly used to thicken dishwashing detergents.
Using dishwash detergents to wash a car would be like using salt water. The obvious results are severe water spotting and the promotion of corrosion.
Carwash: Salt is not commonly added to thicken carwash detergents.
Source: Kim Wilson, US Chemical and Plastics
