I'd say it depends on the pressure. My gas powered one, when at full 3000 psi, and set on fine focus, will eat holes in the concrete deck like nothing. To clean my pool filters, I recently bought a small electric model that's 1700 psi max. I plan to use it on lowest pressure and coupled to a special nozzle that will clean six fin slots at a time. I need to get some spattered concrete off the hood of the BX and would try the little one set on low, but would never apply the big one on high to the general area of the engine. Now the backhoe bucket with dried clay is another story. Sometimes I have to take a small pry bar and chisel that stuff off; the big unit on that and the tires I would do.
BTW, a transformer on the plug steps down the voltage sent through a very long cord to the electric pressure washer. Electricity and water bring memories of scenes in old James Bond movies.