Isuzu Rodeo Runs HOt

I have a 1996 Isuzu Rodeo with 165k miles and I seem to have an issue with it running hot. I can drive the Rodeo for 5 to 8 miles one way and have to place water back in the radiator just to be able to get back to point A. I have changed the thermostat 3 times. I have an appointment for oil change tomorrow. I checked oil and it is Black, very black. So i do see it needs changed. Also I have noticed whenever I put the vehicle in 4x4 it loses power. The dash lights come on then go back off. I figure it was a ground wire shorting out. So I changed all ground wires on top I could find. Havent been under vehicle yet. Whenever I lose my power, cooling fan quits and gets hotter, then when power is restored, fan kicks in, and starts cooling down. But the water in the radiator keeps disappearing, and I have not seen no leakage, where is the water going? Does anyone know what is wrong with my Rodeo.

I have been reading alot of posts and still havent seen the answer. If anyone could guide me, I promise to keep updating until it is fixed so others will know what the problem was. Thank you

Sounds like a blown head gasket or cracked manifold.

What does your exhaust gas look like?