here are the symptoms-

1. little to no heat in cab, with it going from cold to luke warm when i really run her hard and get the engine temp up 190-200*, then the temps will fall rapidly to about 160* and the heat in the cab goes cold again.

2. there is no movement of the coolant in the over flow bottle, its doesnt rise or fall with engine temps ever

3. i hear a rushing/gurgling sound within the heater core behind the dash. i get gurling at low rpms right after start up, kinda goes away as the temperature rises, but then i always have a hissing/rushing fluid sound when above 2,000rpms. there are no internal or external coolant leaks at the heater core tho.

4. last night after going out and getting it up to 190* and driving back to the garage, we opened the rad cap and there was zero pressure built up in the coolant system, and the water at the cap of the radiator was so cool you could easily put your finger in it without getting burned, yet the motor and upper rad hose was hot enough to burn you.

why am i not getting pressure and heat through out the entire system? anyone have a clue here?

 

Ok I will try. First your thermostat seems to be working well, the radiator cool and the engine hot but not overheated. gurgling in the heater is in some cases somewhat normal, but must reflect that air is in the system. You have no pressure which means that there is a leak somewhere. The cap may be bad, or a minor leak somewhere. Need to find and fix that.

Ok now that we established that you have a leak, are you sure that enough coolant is in the system? Forget the tank, is the coolant full? The tank only gives you a level if the overflow system is working which in this case you said it was not. Low coolant or air in the system can give you low heater output. The gurgling sounds to me like you have air in the system.

Once the leaks if any are fixed and the radiator cap is working properly, check the hose to the tank for leaks, put a clamp on each end to seal it and the overflow syste shoud start to work. At first it will pull some coolant into the radiator on an overnight cooling and replace some air with it, than when all the air is out (several cooling cycles) it will start to pull coolant in at night whiile cooling and then expell it when the engine is hot.

 

thanks...what do you mean to clamp both ends of the line...the small hose from the rad cap area to the overflow tank?

 

Make sure the radiator is full and use a 50/50 mixture of distilled water and antifreeze. Sounds like air, make a short trip with the cap loose so it doesn't build pressure make sure its hot enough to open the thermostat. This will burp the system and will not hurt anything. Then top it off with 50/50 coolant mixture.

 

ok well i put a new t-stat in it, and a new cap. had it in the driveway and left the cap off and put a block of wood on the pedal to hold it at 2500rpms. i watched the radiator and at 195* the water started flowing when the t-stat opened. the level in the radiator dropped prolly 8" so i added some 50/50 while it was running until it was just below the top of the radiator and had that little bit of airspace, then put the new cap on and went for a drive. honestly, between the cold weather and traffic i dunno if the t-stat even opened on my trip up thru town.

it never got to 190* on the gauge. but regardless anytime the motor spins over 2k rpms there is the loudest hissing sound (like water coming out of a nozzle at high pressure) as the water is rushing thru the heater core. it isnt leaking out, so there is just some blockage in the core itself. im gonna hook up some hoses to it one day and flush the core out backwards to push any clogs out. thats the last thing i can really think of.

 

any more ideas???

 

Is the t-stat a two stage? I can't remember where I read it, I think Dave Fritz Dodge website, when the primary t-stat opening is closed the secondary recirculates the coolant through the heater core and block. If you installed a cheap t-stat from Azone or others, the t-stat doesn't performe correctly.

It sounds like the t-stat opens at 190 degrees and the cold coolant from the heater core hits the t-stat and closes again. Toyota's are bad for this also.

What kind of t-stant did you install?

 

the one i just took out was only 5 months old, a cummins/dodge replacement. i picked up a stant t-stat from pep boys and threw in there.

i am getting slightly warmer air finally, maybe each time i heat cycle the truck it will purge the air out until it works right. tho i still have the high pressure water rushing sound in the heater core, but the heat is 30-40* warmer than before, still not HOT tho

 

Make sure your overflow bottle is half full or at the line, so it doesn't suck air back into your coolant system.

There's a post active about using dish detergent to flush the coolant system out. read the details, it might help you.

 

just had another thought, one of my heater hoses started to crack...i replaced them with soft flexible goodyear rubber hose from autozone. the hoses are designed with a sharp bend...do you think the hose could be pinching shut going into the core?

i know the system is under pressure normally, but if that hose starts to pinch shut, could it create a vacuum inside the heater core as the flow is being pulled out of the core? i guess ill have someone rev the truck tonight while i watch the hose to see if it flattens out at the bend. if so ill be getting new heater hoses

 

Get the formed hose that belongs on it. Any parts house has them.

 

A pinched hose ahead of the core could account for the sounds you're hearing at the core.