I use old cardboard scraps as scrapers to get the worst off; disposable nitrile gloves are your friend. On one bad job, I started by putting gloves on and scooping handfuls into a bucket. I swear I pulled a gallon of grease of a nasty, little excavator once (Cat 311, if I recall).
@CurlyDave: Please don't just hose it down in the back 40. In a perfect world, you'd be able to clean it on a concrete pad that drained into a separator. That's not always possible but you can try to limit the harm done. I wouldn't want to see that on anybody's land.
I was on one site where the machines were parked in a low spot for pressure washing. It was a horrible mixture of grease and mud that's going to be a remediation nightmare.
How about walking/trailering your machine to the nearest self-serve car wash? Been there and done that to do the preliminary cleaning of components for reman jobs.
As for cleaning machines off, I did a fair bit when I started my apprenticeship. I usually started with a fire hose to knock the worst off; especially for dry mud in track undercarriages....hose, hack with shovel, repeat. The hose is much more effective on heavy stuff than a pressure washer.
For dealing with grease using a pressure washer, a model with a boiler is a must...along with a caustic cleaner. With things like booms, start at the base, and work outwards. You might find yourself just pushing grease around rather than blowing it off, so just push it all to the end and deal with it there.
The most frustrating thing to clean besides the base of an excavator boom, is the centre pivot of an articulated loader: You spray one side...which pushes the grease to the other side. You walk around to spray that side, and push it back to the first side. It gets a little better each time around and you go back and forth until it gets to an acceptable level.
Oh, and put on some raingear that you don't care about and don't need for anything else.
