What exactly does a steam cleaner do to a car, other than maybe clean the upholstery if you have cloth rather than leather seats? Curious why you are apparently using it on the engine.
I live in New England, and this is a 12 year old truck. As far as the engine, It gets the salt, old oil, various fluids and road goop off of it. Mostly because it looks better, but it's also a lot easier to find/diagnose leaks and such if the engine bay is clean. It's also a lot nicer in general to work on a clean motor.
As for the interior, I have Car OCD and I'm a neat freak, so even though this is just my winter car I want it clean (at least on the inside, heh, it's actually covered in mud on the outside right now). It's not just for the upholstery, it gets dust/dirt out everywhere. I did my vents, headliner, dash, carpets, shifter, steering wheel, etc, etc - basically every surface in the truck. The previous owner was a smoker, and the thing smells like a new truck inside now. The fabric's a little wet here, but check out the door panel, keeping in mind that the previous owner was an absolute fucking filthy slob who apparently listed "smoking marlboro reds, 20 at a time, with the windows up and never washing my hands, ever" as his hobby. The thing looks brand new.
It also does an awesome job of getting squashed bugs off the front end, and helps a ton with cleaning your wheels (brake dust), calipers, etc. It's just a fuckin' great way to clean your car all around, and it's only $100.
