My 06 6.0 it blows out cold air after it has ran for 15 min and then when I drive it the are gets hot then it goes to luke warm and then to ice cold my vacume hose was off by the heater core valve so I put it back on and it didnt seem to help at all. Im thinkg that I got another vacume somewhere, because my truck makes a high screaching whistle like its comming from the turbo but I dont think thats it becuse as soon as I step on the brakes when slowing down at a stop sign it quites and then soon as I let off it the noies starts back up again

 

Are you loosing coolant? normally you will lose heat if the coolant is low, make sre it is filled to the MIN line on the coolant bottle, not the max line. also make sure the heat is turned on when adding coolant to make sure the heater core is filled also.

 

my coolant is fine and heat is on i had to the shop about 2 weeks ago and the the mechanic said that it was was because of a cracked head or the gasket was going out but he also said that the enging light would be on if it something was wrong with the engine. but as far as coolant looking bad or greasy its not its clean just like it was brand new and also ive checked the oil and its clean ive replace the tank cap from factory and the new cap had a seal on where the factory cap didnt so would it be worth doing heater core flush or should i just do a valve flush i tend to learn more off of pictures or someone showing me how things are done i greatly appreciate that info your giveing me

 

wht mods have you done to the truck or is it all stock?? that screaming my be pressure coming out of the degass bottle, you can T-tap a pressure guage into the dgas bottle lines up top to see if it is building too much pressure. I bet you have some steam coming out of the exhaust too.

 

i have gauges in the truck thats another thing the mac said was my pressure is around 18-20 psi but also said that shouldnt effect nothing

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so when i go to refill the degass bottle do i leave the truck run or shut it off then fill it to the min just so i know for the future