Stupid Question - I'm just powerwashinng the underside of my H2 and it seems the frame is covered in dark black greasy paint substance. Is that some sort of factory undercoat or something? It's all over the frame. Anyone seen this before? And if so, any suggestions for cleaning it? Or just leave it be?

 

All of GM's frames are e-coated or electric coated to prevent rusting. Try not to hit it directly with the pressure washer it will take it off and you want it to stay on as long as possible we have used a degreaser and that works pretty good. That's why the corrosion warranty is so long on GM vehicles.