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No heat in minivan

I recently purchased a minivan from a family friend and the heater is not working. The vehicle is a 2000 Chrysler Voyager. Here’s what I’ve done and where I’m at:

The coolant in the radiator was low so I filled it up. I ran it multiple times up to operating temperatures to see if it just had an air pocket, but nothing changed.

The car runs right up to temp (220F while sitting) and stays right there. I let it run for quite a while (30 min) so the radiator was really hot and the cooling fans turned on. I checked the heater core lines and one was lukewarm while the other was cold.

I assumed the heater core was plugged so I yanked it out (after a few hours of cursing). There’s nothing wrong with it. Water flows freely through it in either direction without any sign of buildup (I’ve had a plugged heater core in a different vehicle and it was plugged right up). I checked this multiple times because it just didn’t make sense. The heater core looks new on the outside and passes fluid in either direction freely.

I threw that heater core back in, filled the system back up and started it. Ran right up to operating temperatures, shut it off for 3 hours outside, started it again and went on a small errand. Same story, heat up to 220F while sitting idling, lukewarm going into the heater core and cold coming out. Checked the coolant between cool downs and it’s all up.

No idea where to go from here.

if inlet hose is warm and not hot and you know the heater core is not plugged than you have low flow from the heater hose. follow the hose back to motor. its not an old vehicle so the hose routing might not be simple. it might go thru a bypass and other connectors. if hoses are clear than you have poor flow from the waterpump? plugged outlet?

Does it have a rear heater? Your air bubble instinct might be a good one and there could be a problem caused by the long lines to the back heater (assuming you have one).

Other than that, there’s a valve under the dash, near the heater core, I think which I have heard of malfunctioning.