Suburban Heat Issue

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df2x4

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So I pulled my '97 K1500 Suburban out of storage tonight and noticed a strange issue with the heat. It seems to cool off when I come to a stop, or when I turn the blower on high for an extended period of time. Only in the front, the rear system is operating completely normally.

Thermostat was replaced last month with a factory ACDelco 195 degree stat and seems to be functioning normally, coolant temp reads normal. No check engine light, no codes. Fluid levels are fine. No visible leaks.

Am I safe to assume that this is probably just air in the system left over from the thermostat replacement? That's my gut instinct anyway... Seems like if the water pump was going out then the rear heat output would suffer as well. And if the heater core were going, would it just magically start working again when the vehicle was under load?

Any input is welcome, I'm going to try burping the cooling system on a hill tomorrow and see if it helps. Thanks in advance everyone.
 

slowburb

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I'd lean towards one of two causes. Either low coolant level or air in the system.
 

df2x4

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Like I said, fluid levels are fine. Thanks for the reply though, that's confirming my suspicions. Hopefully it's just air.
 

Tech

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Restricted front heater core. Could be plugged with junk and scale flushing may help.
Control valve not fully opening or sticky.
 

df2x4

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Restricted front heater core. Could be plugged with junk and scale flushing may help.
Control valve not fully opening or sticky.

Do these trucks even have a control valve on the coolant? Didn't think that was a thing...

I just let it run for about 45mins on a hill with the cap off. Didn't see any bubbles, but it seems to have helped. Heat works OK idling in the front and rear now.
 

Tech

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Since they have independent front and rear controls there must be some means to adjust the heat but I don't know where it is at either.
 

df2x4

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Ah, yeah sorry misunderstanding on my part. I thought you were talking about an actual valve in the cooling system, like how some older BMWs and stuff actually restrict the flow of coolant through the heater core when you adjust the heat. I think the front and rear systems in these trucks just use dampers in the ducts.
 

SAATR

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There is a valve on the Suburban. It's vacuum actuated, right below the drier. Cuts flow to the front heater core.

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df2x4

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Good to know, thank you! I'll keep this in mind if it starts acting up again.
 
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