No heat with Big Radiator and Electric fans

[1998_K1500_Sub]

the thermostat could also be stuck right....

Possibly…. That could explain the OP’s observations to some extent.

I think @Schurkey is onto a contributing problem for the OP. That air leakage path is an enigma that I suspect few are aware.

This thread could have labeled “No heat” because the radiator and fans aren’t material… but, better to have too much information than too little.

 

[Frank Enstein]

Frank had a large air leak under the coolant recovery tank where the wires came through.

The heat is better but it's still "meh".

I'm planning to remove the HVAC unit from the donor Suburban and replace EVERYTHING!

 

[Schurkey]

I've heard it said that the problem can be solved by coming in through the cowl, i.e., in front of the windshield, to access the "foam" in question.

These pictures, which I copied from GMT400 years ago, show a means of access to at least one "foam" gasket; evidently on the passenger's side there's a panel that one can remove, e.g., with a heat gun, to gain access. @Schurkey, is this gasket the primary culprit? You mentioned "the real problem was above the blower-motor box, where it attaches to the metal of the cowl".

https://www.gmt400.com/attachments/gasket1-jpg.45943/

https://www.gmt400.com/attachments/gasket2-jpg.45944/

You could access the foam gasket in question by reaching down through that opening to where the stamped metal of the cowl mates with the plastic of the heater-blower box. Pack it with caulking or silicone sealer from the inside, and hope it doesn't fall out later ('cause it'd fall into the spinning squirrel-cage of the heater blower.)

Worth a try--depending on how hard it is to remove the panels over that opening.

 

[UsernameRequired]

This may sound crazy, but I lived it. My truck (engine swapped to 350 carb) had no heat, both hoses to the heater core were connected to returns on the water pump and radiator (they'd get hot as well). I had to move a hose to the intake and boom I now have really good heat. I mentioned because of the swap performed, maybe it could be something as simple? I still scratch my head thinking about it.

 

[davkenrem]

Been too cold to do anything. Heavy snow forecast for Wednesday. Will probably leave it for spring.

 

[454cid]

This may sound crazy, but I lived it. My truck (engine swapped to 350 carb) had no heat, both hoses to the heater core were connected to returns on the water pump and radiator (they'd get hot as well). I had to move a hose to the intake and boom I now have really good heat. I mentioned because of the swap performed, maybe it could be something as simple? I still scratch my head thinking about it.

Lol, that's kinda like plugging a power strip into itself!

 

[1989GMCSIERRA]

I have an issue that I could use some help with. Two years ago I did a major upgrade on my 1997 K1500 Suburban. I installed an new L31HD Crate engine. Along with the new engine I did a 0411 PCM Swap, added Electric Fans from a 2005 Suburban Z71 and add a big block radiator. The engine runs VERY cool in the summer. I also put a new dash board in and while I had the dashboard out I installed a new heater core.

The last two winters I have had no heat. I installed a 185 degree thermostat in the vehicle. I have checked both heater hoses and they are hot. I put a piece of wood between the condensor and radiator last night and the coolan temp got up to 210 degrees this morning still no heat. Today the outside temp was 8 degrees and I had the cooling fans disabled. Last week I pulled the dash and checked all the actuators and they all seem to be working. I pulled the blower motor and vaccumed out some debris from in front of the heater core. After I put everything back together I started the truck and let it run for about twenty mins and I had good heat. Until I took it for a drive and with air blowing over radiator it cooled down. Not really sure where to go from here. Anyone have any ideas?

assuming the coolant going to the heater core popes right and is coming off the hot block or waterpump not the cooler radiator……Your cooling system is over cooling the engine.
do yiu have dual fans and are you setting them both to run or is one for engine cooling and the other set to kick on with AC?
1, if you have the fans set up to both come on at the same time unplug one fan see if the temps go to where it’s getting some heat in the cab with only one fan running.
then all you need is to set up the other fan to come on withAC or get. Temp sensor where it kicks the fan on when it hits say 220*

a cheap test is take a piece of cardboard and block off half the radiator. See if the temps go up..

you can retrofit a louver system off a newer truck to partially block off the grille opening amd make it where it opens fully at highway speeds.

 

[1998_K1500_Sub]

assuming the coolant going to the heater core popes right and is coming off the hot block or waterpump not the cooler radiator……Your cooling system is over cooling the engine.

If the thermostat's doing it's job, the engine won't be over-cooled.

 

[strikk]

When I got my ‘95 tbi 454 it wasn't producing any heat. As I was working through the heater box, heater core, hoses, everything was clean and functional. For shots I took a look at the thermostat, the previous owner had put a 185*. Swapped it for a oe spec 195 and the heat immediately started working.

Never dug into why or what but just my 2cents on the topic

 

[thegawd]

That's exactly what I was trying to say. put the correct thermostat in and try again!

when the engine gets to 185°F the thermostat opens and with this huge rad and electric fans it wont ever reach operating temp.

At least that's how I understand it.

I thought those 185 thermostats were designed for extremely high temps like Arizonas summer heat.

CHEERS!