Most roof load boxes are designed to be weather resistant. However, they may not be able to withstand the pressure of the water used in an automatic car wash. If water enters the roof box, it could damage both the inside of the box and any contents left there. It's quite normal that they want you to take them off before they wash the car.
It has to do with liability for possible damage to the car. However, it's safe to assume that car washes generally don't allow vehicles with roof bars for the reasons I mentioned earlier. It is possible to go through a car wash with a roof rack, provided that the car wash company allows it and the car plus the roof rack does not exceed the height limit of the car wash. If they say “yes, that's OK” and you drive your car through the automatic car wash with a roof box on top only to discover that it's damaged, be sure to collect evidence of the damage.
Although roof boxes are designed to protect the contents from the elements, they will no longer protect them from water entering them under such pressure. Any parts that are experiencing wear and tear will need to be replaced before reattaching the roof rack to the car or there is a risk that the parts will come off and cause serious damage. Therefore, although it is possible to go through an automatic car wash with a roof box installed, it is strongly recommended that you do not do so. These experts range from roof box manufacturers to automatic car wash companies and their answers surprised me.
Typical components of a roof rack include the car support bars, the cross bars and the towers that support the cross bars. Take pictures of the scene, and especially any signs that say it's safe to use with a roof box or roof rack. All car washes have the ability to hook into the roof box and remove it from the roof while it is in the middle of the wash. You want to ensure that your roof racks remain in good working condition, so this means regular maintenance to ensure that it stays sturdy and keeps your equipment in place.
Let's take a look at what to look for in a roof box, what options are leading the market, and which ones are best suited for your next big trip. If you have a roof box with no contents inside it when you enter an automatic car wash, then the risk of water entering your trunk is not a big problem. Most, if not all, roof box manufacturers recommend removing your roof box before going through an automatic car wash.
