Heater blowing lukewarm air instead of heat

[jagarundi]

Took my 98 XLT to the brilliant mechanics at Ford on Tuesday. They replaced my water pump, belts, tensioner and flushed the chocolate looking collant out and refilled it. Picked it up this morning (Thursday) and realized that after driving for about 40 minutes or so with the heater on full blast, I was only getting lukewarm heat, and that was when I was rolling along at a 70 - 75mph clip. My heat was working fine before the Ford mechanics got a hold of my truck!! What could've happened with them replacing my water pump and flushing my system that would cause this? I want to be able to do something on my own, because at this point, I truly beleive that I can guess just as good as the Ford mis-chanics.

 

[Blee1099]

Sounds like another blend door problem.. Do a search on blend door.. Theres alot of threads on how to repair it and the symptoms of a faulty blend door. It could also be a bad thermostat..

 

[jagarundi]

But it was working FINE before they did whatever it is they did!

 

[Blee1099]

Probably the thermostat is bad.. I didn't notice in your message whether or not they replaced it.. To replace it, just go to your local parts store and ask for a thermostat for you truck. To replace it, just follow your upper radiator hose to the engine and unbolt the inlet where your hose meets the engine.. Underneath there is the thermostat. Make sure you put it in the right way.

 

[jagarundi]

I don't think they replaced it. It was fine before they flushed my system and replaced the water pump.

 

[briwayjones]

It could have something to do with flushing the system of that old coolant. The heater core uses the hot coolant to create it's heat. I suppose it could possible gotten clogged or something like that.

 

[jgilbs]

when i replaced my water pump i used a little too much RTV sealant. so my tstat failed, i took it out, and sure enough, there was a little chunk of dislodged sealant blocking the stat open. i replaced it and the problem went away.