There's a rig across the street from my house that has some really nasty grime underneath it... looks like a lot of fluids+dirt+sand = caked mud underneath. Some of it may not even come off with anything short of a pressure washer.

Any suggestions?

 

then use a pressure washer.

 

Spray it with degreaser and power wash it a few minutes later. This is how I get mountain bikes spotless at my summer job as a bike mechanic.

 

steam cleaner

 

I was planning on water blasting my runner underneath this weekend,are there any area's to avoid.

 

Go drive it in the river for a few minutes. Then bring it out and spray it down.

 

this is the true way to go. Bit spendier than just pressure washing it, but its also way better (or so i have heard) for the paint, pieces/parts, as you dont have the chance of pushing anything around with the high pressure water. Never had it done myself, but saw a friend who did, and man was it purdy.

 

Brakleen + pressure washer = clean