Inadequate Heat

[Blackbeard44]

I didnt notice the blend door videos, I watched them and they dont look messed up, I'm sure some foam would help, but it should still have heat, how is the airflow, does it blow a good amount of air? maybe the squirrel cage is stripped out on the motor shaft.
One thing I have noticed with my truck is when it is 0°-20° in the AM it can blow so much air it will keep the motor from heating up, I turn it on 1 click once engine temp gets to 110°, than 2nd click at 150° and only put it on its highest speed once fully warmed up and driving

 

[bucket]

Well, I got around to changing the heater core today. Decent heat when the truck is idling for a long time. It will stay at 206*F for a long time before it gets any hotter so that must be where the thermostat opens. But as soon as I start moving it starts cooling down. I have to idle for like 15 minutes to get the electric fans to kick on.

Maybe I need to do the old diesel trick where I block off a portion of my radiator with cardboard to see if I can keep some heat in the thing.

The engine starts cooling down, or just the heater output starts cooling down?

 

[LateOnTheBrakes]

Both. I can actually keep the truck c

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ool with just the heater running at full blast. Air flow is not a problem. It just feels like the air coming out of the duct is no warmer than 50 or 60° f.

 

[SirRobyn0]

Well, I got around to changing the heater core today. Decent heat when the truck is idling for a long time. It will stay at 206*F for a long time before it gets any hotter so that must be where the thermostat opens. But as soon as I start moving it starts cooling down. I have to idle for like 15 minutes to get the electric fans to kick on.

Maybe I need to do the old diesel trick where I block off a portion of my radiator with cardboard to see if I can keep some heat in the thing.

Ya, so a lot of people don't know that the temp printed on the thermostat you probably have a 195 is the temp it starts to open at, fully open is typically 5 to 10 degrees higher, hence your seeing 205 and that's totally normal. @Blackbeard44 is right about the higher the blower setting the cooler the air is and it's just because more cold air is passing though the core. The same thing will happen with A/C too in the summer. So often times the best strategy to cool a vehicle is to start it on the second or third to highest blower setting on rec for a few minutes so the evaporator can get good cold before setting it to full blast to really cool down, and the same thing can apply to heat.

 

[SirRobyn0]

Well, I got around to changing the heater core today. Decent heat when the truck is idling for a long time. It will stay at 206*F for a long time before it gets any hotter so that must be where the thermostat opens. But as soon as I start moving it starts cooling down. I have to idle for like 15 minutes to get the electric fans to kick on.

Maybe I need to do the old diesel trick where I block off a portion of my radiator with cardboard to see if I can keep some heat in the thing.

What are you getting for vent temps now? How cold is it outside? I'll admit to blocking part of my radiator in cold temps in order to keep the engine temps up. That scenario can be somewhat aggravated by a larger than needed radiator.

 

[LateOnTheBrakes]

It was in the 60s today. Heat wasn't even 80.

 

[Bextreme04]

It was in the 60s today. Heat wasn't even 80.

How are your heater lines run? Are they from, and back to, the ports on the pump behind the thermostat housing? My 2011 Suburban with a 5.3 gets up to 210 and locks in there(probably right in that 206 range like yours) with the 195 degree stock thermostat. The heat blows hot as hell in both the front and the rear and makes no difference to engine temp, even on sub-zero days. You obviously have some kind of major issue here.

 

[Bextreme04]

Nevermind, I just went back and looked at your pics from December in the thread. So your connections are correct, and the heat being the same both before and after the core tells me you have an airflow problem through the heater core.

 

[SirRobyn0]

Nevermind, I just went back and looked at your pics from December in the thread. So your connections are correct, and the heat being the same both before and after the core tells me you have an airflow problem through the heater core.

I agree and frankly can't see what else could be the cause.

 

[LateOnTheBrakes]

I definitely think the heater core could be about an inch wider. But I filled in as much as I could with the foam tape that came with the new heater core.

 

[Blackbeard44]

I just did a very quick search for "CUCV heater core difference" and it seems the first 2 thing that come are people having issues with a replacement core, GM must of had a different spec for the CUCV trucks

 

[LateOnTheBrakes]

It wouldn't be the first time the mix of military and civilian parts screwed me. I'll spend some time tomorrow looking at the tech manuals for the M1008 and see if I can get a part number to cross reference.

For what it is worth the only options I see are air conditioning or non-air conditioning. The size of the air conditioned one looks better to fill the HVAC box but the holes in the firewall line up with the non AC version.

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[MBC25]

Check both hoses for heat in and out if both hot look for delivery door inop

 

[LateOnTheBrakes]

CUCV Replacement Heater Cores - No or Low Heat Output Reason

I had to replace my heater core back in the summer because my original core was leaking. It has just now gotten cold enough to start requiring heat and I soon found out I was not getting heat like so many others on the site who have replaced their original heater cores. I did not want to spend...

www.steelsoldiers.com

 

[Blackbeard44]

i did read a little ways into one of those articles and someone posted a part # of what they used to fix it.