Ok the truck was laid up for two months while i rebuilt the engine and now no heat(very little). I removed the trans cooling unit under the intake manifold and bypassed it with 5/8 hosing. Thermastat opens when i put it in front of the jet heater and then closes when i remove it. Everything worked fine prior to the engine removal. All heater hoses are hot except for the lower heatercore hose? Seems like there is no flow. Top core hose that goes to the head, that is a little hot but the bottom hose is much cooler. Air pocket?
Anyone have any thoughts???
05 3500 dodge cummins...

 

probably air locked, try taking the radiater cap off on a cool start up and squeeze the hoses, radiater and heater. dont know if this will work for you, but i did have to do this on my wifes car when i replaced the motor in it. i'm sure someone on here way more experienced will probably lead you in a better direction, fit for the cummins. Good Luck

 

IIRC the heater hoses are tied in to the trans cooler, with your by pass hose installed now, it may not be flowing through the core, try pinching that new line off, or removing it completely, thats what i did

 

Many thanks for the responses... I pinches the hose going to the drivers side of the block forcing water to flow threw the core.. but still no heat. I left the cap off for hours also.. So i have a air pocket or the heater door is not opening? Anyone know how to check to see if the heater door is opperating? When truck is hot and i turn the heater control **** from hot to cold, i do feel it getting colder and when i go back to hot it gets a tad warmer but not much...??? The lower hose from the front of block to the heater core is still cooler than the rest of the hoses...?