I have a 1989 pickup v6 4x4 and have no heat. Replaced thermostat and water pump works great blower runs and can hear water running through hoses. For about six months the heat would work for about ten to twenty miles then blow cold now it just blows cold all the time. Help please it's cold as hell outside

 

All cables on the heater control working correctly? Heater valve on firewall is opening properly? Is heater core caked with dirt so it cannot exchange heat properly

There are a couple of other threads recently with similar lack of heat issues.

 

Will check those better tomorrow morning
And get back

 

Just checked the cables valve and core but everything looks and works fine found some tight bends in hoses but fixed that

 

Ah, those tight bends may have been collapsing closed when the rubber warmed up.