This isn't a problem with my truck, but my buddy has a 89 Jeep Wrangler and has a problem with the heater. It blows a normal volume of air, but it's warm air. When the engine is heated up and you have the heat off for a little while, when you turn it on, its warm for 5 seconds and then goes back to being cold. This a problem with the heater core?

 

It could be the heater core, thermostat, or blockage some where. I would first check the tubes running into the heater core and see if water is flowing. If there is water check to see if it is hot. If there is water and it is hot then check the return tube to the radiator. If the return tube is not returning water then there is a blockage somewhere.....

 

ok i'll check that out...thanks.