98 Durango Magnum V8 5.7

Seems when I drive my truck after its warmed up that I get decent warm air coming out the vents while im driving but when I say get to a stoplight or anywhere Im at a standstill it blows cooler, go back to accelerating and driving it warms up again, Is this a thermostat fritzin out?

 

could be the t-stat, could also be a clog in the heater core or somewhere else.. could also be the water pump but you not overheating so i would say that is a slim chance... i would flush the system and get a freash t-stat and antifreeze in there then see if the issue presists

 

sounds to me like a weak water pump tbh,

also you do NOT have a 5.7 im not sure if you have the 5.2 or 5.9 but its one of those

 

I had the same problem. Back flushed the heater core, works great ever since.

 

So say would I want to 1st take it & get the Coolant system flushed out & get some new coolant & see if that resolves it & if not then move to the Thermostat if that doesnt resolve it?

 

Well take and touch the heater lines once it is warm, use gloves, if the in is hot and the out is cool then your core is plugged.