Heater blows out hot air on low fan speeds but not on highs

2002 DODGE RAM
148,000 MILES • 5.9L • V8 • 4WD • AUTOMATIC
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JEEP769
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  • 51 POSTS
I have a 2002 Dodge ram 1500 4x4 SLT quad cab. I've just noticed the heat only works when the fan is on the low settings. When I put it on Max fan speed it blows out just like 70° 60° air. And being in Iowa in the winter I kind of need it a little bit warmer than that. Don't know what is wrong with it or which direction I need to go first I did fill it with antifreeze which did help it a little but it's still full and it's still doing the same thing not really sure what I could try any help would be very helpful thanks
Dec 26, 2022 at 3:59 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

If the coolant is full, my next question is if the engine is reaching operating temperature. The thermostat may be hanging open a bit and the engine can't fully warm up.

Take a look at this link:

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

Let me know about the engine temperature. If it is hot when on low speed, and cools off when the fan is on high, it sounds like either we have restricted flow via the heater core, or the engine isn't getting warm enough.

Let me know.

Joe
Dec 29, 2022 at 1:58 PM
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JEEP769
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  • 51 POSTS
Well, I figured out that the engine is getting about Midway on the temperature gauge which I think is normal operating temperature I can send a video of it and then when I turn the thin on the high speed the temperature does go down a little bit it's kind of hard to tell but it looks like it does go down just a little bit to me so you're thinking that would be the heater core being restricted or just needs a new heater core? Thanks for all your info and help from before on the first question.
Jan 5, 2023 at 9:18 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
I would first check to see if one of the heater hoses at the firewall cools off and the inside temperature cools. If it does, try flushing it first. If there is a restriction and you can't clear it, then replace it.

You don't want to replace it unless we are absolutely sure it is faulty. Let me know what you find, and I'll walk you through the flush process if needed.

Take care of yourself.

Joe
Jan 5, 2023 at 12:59 PM
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