Heater works intermittently?

2008 DODGE GRAND CARAVAN
270,000 MILES • 4.1L • 6 CYL • 2WD • AUTOMATIC
Avatar
RICHARD BYERS
  • MEMBER
  • 4 POSTS
The heater will work only intermittently. Once the van has been running for a while, if I turn on the hot air vents, sometimes hot air will blow out right away as it should. No issue.
But sometimes it's still cool air coming in and if I keep it on, several minutes later, hot air will finally start to be blowing out and all is fine. But that is only temporary as after a variable period of time, 2-10minutes say, the hot air becomes a blend as it transitions out to what eventually is just cold air again. Then if I leave it on, eventually the hot air will come back out again and so on.
What might the issue be? It doesn’t make sense.
Jan 23, 2023 at 10:23 PM
Advertisement
Avatar
STEVE W.
  • CERTIFIED EXPERT
  • 15,113 POSTS
The first item to check is your coolant level. Heat that comes and goes like that is common if the coolant gets low and allows air into the system as the heater cores get air locked very easily due to the way the hoses are run and how the core is designed. So, check that first.
Next would be if the thermostat wasn't operating properly. In this case that would normally set a code and turn on the CEL as the computer calculates how long it takes the engine to warm up under a certain load. Is the check engine light on? If yes then see about getting the code(s) scanned at one of the parts stores that do it, write down whatever codes they tell you. A common one for a bad thermostat is P0128, it basically means the thermostat is stuck open and keeps the engine running cold. In your case though it sounds more like low coolant. One item that can really help on the vans and others that have a propensity of air locking is to use a vacuum filling device on the cooling system such as the attached image. However normal purge can work if it's low. The other issue would be that if it is low where did the coolant go? That could be a leak. To find that you would use a pressure test kit. Sort of the opposite of the vacuum fill.
Now if you look at the coolant level and it is full, and the CEL is off and you still have odd heat it could be a faulty blend door actuator, however that will usually show up as heat on the driver's side but not the passengers or reversed or no rear heat but still front heat.

https://www.2carpros.com/articles/car-heater-not-working

So, a few questions, Is the coolant full? Do you get heat on one side but not the other? Is the CEL on? Check those things first and we have a starting point.
Image (Click to enlarge)
Attached Media
Jan 24, 2023 at 6:51 AM
Avatar
RICHARD BYERS
  • MEMBER
  • 4 POSTS
I added some coolant, yes it was low. Seems to be working now so thanks for the great suggestion!
Jan 30, 2023 at 5:25 PM
Advertisement
Avatar
STEVE W.
  • CERTIFIED EXPERT
  • 15,113 POSTS
Okay, if it was low you might want to watch the level. You may have a small leak that hasn't been noticed yet. If it has the rear heat option, the lines under the car like to leak at the connections in the rear.
Jan 30, 2023 at 7:07 PM
Avatar
RICHARD BYERS
  • MEMBER
  • 4 POSTS
Okay. I’ll keep my eyes out for that.
Jan 30, 2023 at 7:21 PM
Avatar
STRAILER
  • CERTIFIED EXPERT
  • 53,854 POSTS
STEVE W. is one of our best! please let us know what happens.
Feb 3, 2023 at 10:43 AM
Avatar
RICHARD BYERS
  • MEMBER
  • 4 POSTS
It’s working as it should now!
Thanks Steve
Feb 3, 2023 at 4:54 PM