Slide the cardboard down in between the rad and the trans cooler and ac condenser!

 

I thought about that and taped off the fan to see if it made a difference. It didn't. It does take a long time to warm up, but I get heat when the gauge starts to move. I can tell a little difference in heat once the thermostat opens and I can see the temp gauge drop back slightly. I already have the prestone kit on my truck so bleeding the core won't be a big deal. I hate to think that the water pump doesn't make enough pressure to force air out, but I can see that there could be air trapped because the core sits higher than the radiator. Kind of a dumb design.

 

i went through the same thing last winter. i bought a back flushing kit at the auto parts store and flushed it several times. the crap that came out was incredible. worth a shot. i know you just put a new radiator in but maybe your water pump is full of junk? good luck

 

Yesterday i took the radiator cap off when the truck was cold, i ran the engine. after the temp gauge got to normal i ran it at varying rpms for 1/2 an hour. (the truck was not moving) the antifreeze in the radiator was cold. not even warm, it was cold, as was the lower radiator hose.

 

something new. yesterday coming home from work the heater was working perfectly. had hot heat blowing out when i would come to a stop. Now today i took a 20 mile drive and every time i came to a stop the heater would start blowing cold air again. I am lost. it's driving me nuts.

 

So far I am leaning towards the blend door or an air conditioning problem with my 99. So far I have checked the coolant level and all hoses both cold and at operating temp. I noticed my air conditioner compressor is running in heat postions, even with the heat selector all the way HOT. I pulled the compressor clutch connector and things are much better, but something obviously isn't right. Still searchin in the cold......

 

The AC runs to keep the condensation down when on defrost, and to keep it and the AC system lubed up and moving during long periods of non use, like in winter.

 

I have a 2000 2500 with the same flipin' problem! Heater core leaked so I replaced it and now no heat at idle. Removed (I thought) all the air from the cooling system (several times with no real big amount of it!), replaced thermostat, water pump and belt and still no heat at idle. Core inlet hose is burning hot and return hose is the same. Blend door servo motor is moving blend door fully open. It's electric and not vacuum operated so not a vacuum issue. I'm lost!! Tried bleeding more air out of it today and got maybe 2 more cups of antifreeze in it. I can't figure this one out. I've thrown a bunch of money at it and now there is nothing left to replace. Have you guys figured this one out on your trucks yet?

 

97 ram 3.9 liter 6 same deal, no heat at idle. I flushed my cooling system last year purged it and tried getting all the air out. I get a gurgle out of my heater core sometimes as if it still has air in it.

 

My 01 has the same issue, I'm having a hell of a time getting the air out of the system, have tried purging 5 or 6 times this winter.. I even adjusted my electric fan up to 200 instead of 180 and put some cardboard in, it warms the temp gauge up faster, but doesnt help the heater much. I kind of gave up on it.