bought an 06 6cyl Nissan Frontier and the odometer says 18,000 miles (Looks like 118,000). I bought it sight unseen at an online auto auction and paid way, way, too much. I unloaded it at a terrible loss telling the buyer what was wrong with the vehicle and he bought it anyway. But here's my question: I was driveing it and the temp gauge registered HOT. Engine started to sputter, and quit. Pulled to the side of the road and saw that the radiator was low so I put water into the unit and the engine made a cracking sound. I know from experience that one doesn't put water into a hot engine as it could crack the block but....So I filled the radiator and water came out the "weep" hole in the muffler (a lot) and the radiator level went DOWN. I think it had a cracked head or block. I checked the oil level and I'm sure I saw water in the oil. I believe the engine is shot what do you think?

Sure sounds like it to me.

I know it a used vehicle from an auction .
But ,take it to Nissan ,maybe there is some warranty on the vehicle still.( or call first with the VIN number and see if it still has warranty left)
They may or may not honor any warranty based on the findings.
Make sure the vehicle is titled to his(owners) name and not in a business(used car dealer) name.
Worth a try...nothing to loose.

Jim