The pressure cleaner is one tool I wouldn't be without, in fact I just got another one for the summer house. The one at home is a Kärcher 620M, pressure adjustable from 20 to 130 bar, water flow rate 500 l/h.

Apart from rinsing the underbody, I also use the washer for pre-washing the car during wintertime. I like to get as much as possible of the various particles off the car before I attack it with the sponge. As lots of people around here use studded tires, the cars get covered quickly with tar, road particles etc. torn up by the studs. But you need to be careful: low pressure, work at a sharp angle - in general, use your common sense.

Erling.
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1987 240 GL 81K miles