My current job is driving railroad crews to where they need to go, and half of the places I need to get them to is offroad and poorly maintained (if maintained at all). I drive the company's 2006 Chevy Suburban with 4WD.

This is a high-rainfall area, and sometimes I have to go through deep water. I am okay with this as long as I have some idea what I'm doing. I know to go very slowly.

My question: how deep can I go safely? If I had a crew member hanging out the front window to visually check the depth, how deep is where we're getting too deep? To the bottom of the doors? Or is that pushing it?

Also, there seems to be Upper and Lower 4WD buttons. I've used the upper one when I've need to, but never the lower one. What is the difference?

Any info and tips welcome.

Sue