PO172 is the code for RICH EXHAUST just like i said!!! If "water" were getting into the engine oil, then your radiator level will be low!!! Engine should be getting hot!!! Take this vehicle to a MECHANIC and have what is called a combustion leak test perfomed and scan tested.
That will tell for SURE if head gasket is bad!!! Black smoke is the result of flooding, just like it was with the older cars when the choke would stick closed.
Head gasket blown will make white smoke and a bunch of it. Head gasket is the least likely cause of "water" in crankcase oil anyway, this is a very common mistake, intake manifold gaskets is the most likely cause of water in oil...then after everybody replaces the head gaskets, in that process the real problem is fixed by defalt because new intake gaskets are installed!! Rarely see an inline engine with water in oil,wonder why?
Don't have money to take it to mech he said he has this thing to test to see if its something else but the black stuff looks like oil that came out tailpipe it's on the ground so what else do u think it could be
Find another "mechanic", Find a PAT that knows how to look at the data coming out of the scanner not a code reader.
Trust me I know what it means to have a "lack of funds". Don't guess at this. Black smoke is NOT an indication of a blown headgasket!
The P0172 code is an indication of a fuel control problem not a headgasket.
Sorry I know I've not been much help.