why would the heater on ford ranger go out

your automobile has had it my son could be a blown headgasket, check for back pressure on the cooling system on cold start.

Tom has a good point, but also there is a vacuum operated valve in-line on the heater core supply hose that can become stuck or vacuum line detach. I'm not sure what year this is, I think 1999 but will be similar or same, it is Ranger