This might have been talk about before but. i have an 03 3.4 LS the intake gasket has been replaced along with t/stat,water pump. Well the problem i have is the 1st i drive it for the day i get a lil heat then it goes away and the temp gauge climbs to about 3/ 4 back to 195 but still no heat.I've noticed the return tube is cool I've flushed the heater core doesn't seemed plugged. I'm betting i have air in the lines. any comments will be help full thanks

 

first off: welcome to mcf.

possibly air in the lines, bleed the system to get all air out is the first place to start. did you flush the radiator out with a garden hose to get all the gunk out when the intake gaskets were changed?

 

Sorry. took so long to write back. i reflushed the system still have the same problem the messed up part is that i really only have the problem in the morning at the end of the work day every thing works fine

 

Sounds to me like a Tstat issue....
Working intermittenly....
prolly stuck open...if your not haveing any overheating issues....

 

I had that problem on my 3.1 LS, The upper hose would collapse after you drove it a while.
I replaced the upper & lower & also found a glop of goo (Antifreeze) after I flushed it out...

 

The messed up part is when u first drive it for the day. it might blow heat if it does a lily bit later it'll get cool then the temp gauge will climb

 

Sounds a lot like a thermostat to me!....
Even if you replaced it beforre....they have no rhyme or reason to go bad....could have been faulty when you bought it!

 

Thanks for the help ill give it a try

 

Found out the problem headgasket was bad leaking 1-3 and water jacket to 2. thanks everyone that tried to help.