Bingo. Burp the system. I'd bet my left nut you'll get your hot air back.

 

Ok I'm new to this so could you tell step by step how I would perform this task thank ramrunner

 

A lot of people fill the radiator, start the truck and let the coolant cycle with the cap off, topping off as they go. The problem with this is that the engine won't reach full operating temperature with the cap off because it's a pressurized system. It's likely that the thermostat won't open because of this. There is a bypass hole in the thermostat (two, if you're using a genuine Cummins part) that will slowly let air out, but you'll be there forever.

There's more than one way to skin a cat, but I remove a coolant port plug as I fill it. This gets most of the air out immediately. When it's full, I replace the plug and the cap, bring the engine to operating temperature and turn the heater all the way up. You'll know your thermostat is opening if you pinch the upper radiator hose and feel a rush of coolant when you release it (be careful: the hose will be hot). Let the engine cool, remove the radiator cap and top it off. You may have to repeat the cycle a few times to get all of the air completely purged. Don't forget to mind the overflow reservoir.

 

Well thank you for the info.i just got this truck.only had 149000 when I got it.so I'm learning so please bare with me..my truck one day just happened to get and run a lot quiet than normal can someone explain did the truck break in or what.car fax was a 91 check out good so I bought it payed 15000 for it is that to much

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Mr beard or ram runner can you help with this

 

No problem, dude. That's the point of the forum. Learn some stuff, share some stuff.

At 150k, your truck was plenty broken in already. "A lot quieter" is a pretty vague description and I'd personally be more concerned with "a lot noisier". It could be that it was making racket from bad fuel and the new fuel you put in it helped with noise (I sometimes run WMO in the Summer and that makes my 2nd gen 12v much quieter because of the thicker "fuel" with added lubricity). I've seen exhaust leaks "fix" themselves by sealing the leak with soot, too, quieting things down. If the truck is running normally, has good oil and fuel pressure, normal EGTs (depending on your mods) and is otherwise mechanically sound, I wouldn't worry about less noise. It could be that you just got used to diesel rattle.