2005 Dodge Caravan heater issue. One day the heater is working normal, the next day, it's blowing out cold air....thermostat or heater core..will flushing system help determine problem?

you have a clogged heater core and needs to be replaced, this van has only one heater core am i right? check the thermostat too but i think is the heater core

Heater core could be blocked up, or the blend door is stuck on the cold side of the a/c evaporator or the blend door is stuck in the cold position.

sounds like you have a actuator problem or the heater core may be stoped up check and make sure actuator is moving if not replace

make sure both heater core hoses are hot to touch at operating temp if both are not hot replace heater core

and of course check your coolant/antifreeze and insure it is full no water no heat

First of all make sure your anti-freeze is at specification level's as well as make sure With the engine cold start the vehicle remove the radiator cap and make sure you see the flow of anti-freeze while keeping your hands as well as your clothing away from moving parts feel both hoses going into your heater core if the one on top of hot one on the bottom is cold then you have a Clogged heater core in which case you will need to flush the system . a simple garden hose will do the trick simply remove Both hoses to the heater core with the hose at the bottom line apply the garden hose until liquid comes out at the top of the other hose will probably see a lot of gunk. Also ensure that the vacuum line to the round ball under the hood is connected and not dry rotted.this will cause a vacuum leak to not allow the switch to fully engage from cold to hot. I hope this helps you.

If the temperature gauge is reading normal, have the heater control valve checked.

You have a circulation problem, heater core may have restriction that why heat only comes when you drive ,also you may have a thermostat that stuck in the open position. Good Luck

In this order check the following:
Antifreeze level
thermostat
blend door
blend door motor...accordianman

That was a common complaint a few years back, due to the fact that the heater core is a little too much higher than the engine, which requires that extra push it gets when engine RPM's increase. One thing I did do on my Caravan was remove my hoses to the heater core, and use a small external pump with hoses to circulate C.L.R. through my core for a while, then let it sit with CLR in the core overnight.Next day I circulated it through again, both ways by reversing hoses, and then re-attached hoses, bled air out of system, and notice quite an improvement in heat at idle. Once cleaned out, the heater core allowed coolant flow through it better at idle. If your stumped by explanation, take it to an automotive shop, or a Rad shop, and get a quote on flushing that core out for you. I recommend the CLR, but it might be too time consuming for you , but a flush will probably show some noticeable improvement.

check the coolant level, I had the same problem low coolant level.....no hot water to the the heater coil.

my 2000 dodge caravan heat sometime working sometime not working