Doing engines outside a shop is, IMO, sketchy at best, particularly heavy duty cleaning. For interiors, I find the
VX 5000 is more than enough. The steam comes out at around 300 degrees so it gets the work done with very little wetting, particularly the way I've started doing it. - Spray a light mist of interior/carpet cleaner onto the surface, agitate with a brush, hit with the steam cleaner and a cloth at the same time and done.
Granted, I don't do the shoveling out kind of detailing an extractor is made for so I can use lighter equipment. Still, that machine runs reliably and for long enough to do a typical car with water left over.
When it comes to engines, I have a pattern and practice response: First, look at the engine and decide if it can be done at all outside a shop where there's run off control. If there's more than about one tablespoon of oil and grease, I won't touch it. Second, even though I've got a very safe product for removing oil and grease - one that doesn't turn plastic white or hurt the paint, or wiring, there's still a chance of water getting into a connection and shorting out a system. So, I say to my client, "I'm not going to charge extra for cleaning this engine and because I'm doing it for free I'm accepting any liability on any level. I'll be careful, but when I'm getting an engine wet and using any cleaner, there's a chance of problems. Also, if there's a problem with the EPA or any other governing body, it's your problem. So, just to review, if the engine never runs again and the water quality district comes up and assesses a fine, it's on you, and, you still have to pay me for the detail."
Robert