They don t have a quick payback even if you have a great location. The initial overhead for parts and a location is generally very high. Definitely a sustainable business model, but don t expect a positive ROI right out of the gate.
There are one or two forums out there for car wash owners, do a search for them. They have a ton of information about building, running, and maintenance costs.But to answer your question, it all depends on location. Get a good location and they can be a cash cow, pick a bad location and it can be a dog.