No heat with Big Radiator and Electric fans

davkenrem

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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?
 

Schurkey

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When that was my '88 K1500, and I had to wear a snowmobile suit on the 35-mile highway drive to work...



...it wasn't the heater at all. It was a huge cold-air leak under the dash, where the air coming down from the cowl opening ahead of the windshield leaked out of the ductwork before it could be routed to the fan.

The heater ductwork was sealed with foam gaskets. The foam turned to jelly--really disgusting stuff. I had to take the dash apart to remove the "foam" and replace it with strips of weatherstrip foam from the Home Improvement store. I replace all the "foam" gaskets while I was in there, but the real problem was above the blower-motor box, where it attaches to the metal of the cowl.

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davkenrem

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UGH, I do not want to take that dash board out again...
 

evilunclegrimace

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When that was my '88 K1500, and I had to wear a snowmobile suit on the 35-mile highway drive to work...



...it wasn't the heater at all. It was a huge cold-air leak under the dash, where the air coming down from the cowl opening ahead of the windshield leaked out of the ductwork before it could be routed to the fan.

The heater ductwork was sealed with foam gaskets. The foam turned to jelly--really disgusting stuff. I had to take the dash apart to remove the "foam" and replace it with strips of weatherstrip foam from the Home Improvement store. I replace all the "foam" gaskets while I was in there, but the real problem was above the blower-motor box, where it attaches to the metal of the cowl.

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I had to do this to the '92 and it made a world of difference. I am afraid that the '98 has the same issue and I am not looking forward to pulling that dash at all.
 

thegawd

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try changing the thermostat to the correct one. that way the engine will get a bit warmer before cooling it down with those fans. it should be obvious that if it cant reach operating temperature than it will never get warm enough to blow warm air.
 

1998_K1500_Sub

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It was a huge cold-air leak under the dash, where the air coming down from the cowl opening ahead of the windshield leaked out of the ductwork before it could be routed to the fan.

The heater ductwork was sealed with foam gaskets. The foam turned to jelly--really disgusting stuff. I had to take the dash apart to remove the "foam" and replace it with strips of weatherstrip foam from the Home Improvement store.

My Suburban has this problem too... cold air blows into the passenger's footwell area from a leak behind the dash.

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".


 

1998_K1500_Sub

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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.

If both hoses are hot, the problem is in the HVAC system, e.g., airflow being restricted or mis-directed around the heater core.

If one hose was hot and the other was cold, you would have a coolant flow inadequacy through the heater core (for whatever reason). That's evidently not your problem.

Your thermostat temp is plenty high for adequate heat.

DO check with a scan tool to make sure your engine temp (as measured by the ECU) jibes with the thermostat you've installed. The engine should not run any cooler than the thermostat temp in summer or winter; radiator size doesn't matter. The engine should always be at or above that temperature, once warmed-up; if not, you've a problem... most likely with the thermostat.

Radiator size matters once the thermostat is open... in a properly functioning system anyway.
 
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thegawd

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I thought the point of the lower temp thermostat was for hot places, like Arizona? therefore when its -30 it would be absolutely detrimental for correct operating temps?

sure I could be wrong but that's what I understood.
 

1998_K1500_Sub

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I thought the point of the lower temp thermostat was for hot places, like Arizona? therefore when its -30 it would be absolutely detrimental for correct operating temps?

sure I could be wrong but that's what I understood.

The radiator won't dump heat into the airflow until the thermostat opens, that's known. So the engine temp's always at (within a few degrees, anyway) or above the thermostat temp, once "warmed-up".

Opening the thermostat at a lower temp may allow the engine to run cooler, if the radiator has the ability to transfer the waste heat when exposed to sufficient ambient temperature airflow. If...

At the end of the day, it's a "how much heat does the engine reject into the coolant" vs "how much temperature rise is required for the mass of air through the radiator in order to remove that heat". Once those two processes are in balance, the engine temp will be static. Opening the thermostat at a lower temperature shouldn't have much, if any, effect on that equilibrium.

I await the ensuing "corrections" to be posted by others :)
 
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thegawd

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Hahaha I appreciate your response and I do somewhat agree.

I guess real world temperatures need to be observed.

to the OP.... do you have an infrared thermometer to actually check things out?

the thermostat could also be stuck right....
 
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