ok been chasing water lines trying to figure out why i got no heat ...can someone tell me what this is, water line coming out of core goes down backside of alt. around oil filter along side of block to bellhousing into canister of some sort then back to tstat housing ..what is this?

 

Thats your heat exchanger.

 

what does it do? and if its bad is that why i get no heat in cab?

 

it cools and warms the transmission using your radiator
Have you checked the T stat? is your gauge showing heat?
its rare for them to go bad

 

working on #4 tstat #3 rad. temp never gets over 150 160, and i pull 4000lb trailer all day. last week was -40 with no cab heat i dont have to say more. i have found other threads about guys with no cab heat but no fix. some guys say they roast marshmellos in theirs, so why is mine diff. some said if air got into system the core would vapor lock? when my temp gets to 160 ish if i turn heat on it will cool instantly. yes i checked other 3 tstats and they open in boiling water? also rad fluid is weak just to get more heat..

 

I think the valve that controls coolant flow is bad or your blend door is stuck open /broken or has a bad seal

 

what brand of stat are you using? cummins will be the best, second best (but less cab heat) is a stant.

if you cant get to 190, its a faulty thermostat (or your gauge is giving a wrong reading)

there are somethings that you can do to improve heat output.
1) flush the core or replace it
2) prop the recirc door open as a test turn heat to hot, and vent selector on max AC, usually the heater output will increase 20-40%
as the interior air is re-heated instead of ice cold outside air.

 

just because they open in boiling water means nothing, it depends on what temp they start to open. I've changed 5 (yup 5) before getting a decent one on an old 96 dodge shadow, everyone of them did something different, they were motorad brand and in my opinion junk

 

Run your heater with the vent control in the recirculate position and it will cook you out of the cab.

 

thanks for the info guys...the tstat im useing are from auto zone not sure brand but i will go get a cummins one from dodge... also have checked the blend door but i will.. what is the valve controlling coolant you lost me on that one..dont know if this helps but .. today i drove about 15 miles its about 10 deg out side, when i got home i checked the lines to and from core, the line going to core is to hot to hold, the line coming out is luke warm? is core pluged because i did flush the core and it seemed ok.

 

There is no valve in the heater core lines, it circulates constantly regardless of heater control position.

 

You could be air locked, have air trapped in the line as well.

 

ok thanks for all the input guys...i tried the blend door seems good opens and closes with the selector...tried the selector in the a/c max posistion heat went up a little but not hot or even luke warm just not freezing air....still thinking core is vapor looked cuz like i said line in is to hot to hold line out is warmish so seems to me that hot water is not going throught the core, but i flushed it and got good clean water out both ways...how do i bleed the air out anyone done this? also while runig in the a/c max posistion all windows fogged to the point i couldnt see..thinking about electric cab heat as infidel sug. thanks for your help.

 

I never recommended electric heat but if both your hoses aren't hot you likely need a new heater core.
Best way> https://www.dieseltruckresource.com/...d.php?t=229112

 

sorry infidel must of got you mix up with someone eles it was on differant tread about heat...only one line is not getting hot its the line out.