I wouldn't want to use a pressure washer, that is a bit too strong. Could easily eat through gaskets and if you have a weak or dry seal on the firewall, well, say hello mushy carpet.

Nah, it's not really a problem. Just be careful not to spray anything sensitive (gaskets, seals, electronics) and you'll do fine.

My Dart has a total of about 15 years worth of sitting under an old tree, not to mention the long service life before that (200,000+) miles, so you can imagine the dirt and grime that was coating *everything*. About two hours with the pressure washer, and the car is absolutely clean inside and out.