My heater blows warm air at idle (6-800 rpm's) but i have to get the rpm's up about 1000 for it to blow hot air. Normally i thought this was do to low coolant, but my coolant is full so i am not sure what else would cause this.

 

Your heater core could be plugged up causing the coolant to flow slower and making it not blow hot out the vents.

 

Well when I did my plenum I changed the water pump, t-stat, and flushed the entire cooling system (motor, rad, and heater core). After I did that my heat temp went down. I had a 180* stat at first then changed to a 192* a couple weeks ago. It went up some but still feels cooler than it did before the plenum.

So, basically what I'm thinking is that on my problem, the coolant is accually flowing better now.

The heat will drop at idle, at least has on every vehicle I've owned. Did this just start happening? Or has it been this way for awhile?

 

it just started happening, All of a sudden at intersections im having to shift into neutral and rev my engine to heat up the cab. Im in Denver as well. so its around 20 degrees when i go to work. I just replaced my bypass hose and t stat about 3k miles ago.

Could i disconnect the hoses under the hood that run to the heater core and hook them up to a water hose or something to check the flow?

 

Sounds like you still have a thermostat problem or heater core. How did you flush it? Are you sure you don't have air in the system? (jsut asking) I've seen air cause this exact problem. Running water in one direction in heater core to flush isn't good enough.. If you flushing heater core you need to run hot (best) water thru one way, then blow it out gently wiith air if you can. then go other direction, back and forth several time until no sediment of any kind is coming out. I usually use a big coolant drain pan and put the hose i'm coming out of heater core with into pan so i can see if anything is coming out. I have had a few heater cores that i spent the better part or an hour or more just flushing back and forth before i was comfortable with the flow. I have seen some vehicles that this doesn't help either. Most of the time this will work for a while. These can be decieving because it can go in and right back out the other tube without flowing thru the rest of the core. Try flushing it again and watch the stuff coming out. good luck

 

Or an air pocket in the heater core yet. They are a major pain to bleed out.

 

yes they are, My brother in law changed a hose on radiator and lost his heat, When he called i told him it sounded like air in system, He drove it for a week or better making sure he got it up to temp and finally got the air out and his heat came back, That's about the only way to dot it if you dont know how to bleed it, He didn't know anything about vehicles

 

Ok. I didnt actually flush the system when i changed out the t stat. At the time i was short on cash and could spare the extra few dollars. What is the proper way to do a radiator flush? Ive seen some videos on youtube where they have a fitting to hook a water hose up to it to flush it and others where they add a bottle of radiator flush to the system and fill with water to flush it. Are those both correct ways?

 

Couple different ways to do it. Both you mentioned are viable options. Just depends on which way ya wanna run. Having the neat machine to do it is really best...... but, gotta pay someone else to do that. (I really can't justify the cost of a flush machine, for anyone other than a business.)

 

Had the same problem. burped and burped and burped....no change. disconnected hoses, (well cut one and disconnected the other at the water pump) Put in splice and added extra length of hose to side that is not connected to pump.

Enter air compressor, 90'ish psi. Filled core with water. stuck air hose into core hose that connects to pump.
Opened air compressor valve until no more water (you'll hear the difference).

Filled core with water, blew out with air at 90 or so psi. Repeated 4 times or so. Lots of brownish tan gunk comes out. Air is now roasting me out of the cab.

I fought with the CLR treatment, coolant system treatment, back-flush, etc and got mediocre results. Blast the b!tch out with air when it's full and water and a lot of clog comes right out. If you use a nozzle on the end of your air hose, remove the restricter tip so you get more air flow.