Originally Posted by apensity
So sometimes my '01 1500 318 will blow hot through dash, then get cold, then get hot again, then cold... I can hear gurgling behind the dash quite often, but not necessarily when temperature of air changes coming through vents. Also, my temp gauge goes up quickly to like 3/4 (even when it is like 50 degrees out) and then it will drop to less than 1/2 in a matter of a few seconds, then the hot air comes out of the vents. Totally confused here. Have checked MANY posts, but none describe this issue that I have seen, so sorry if it is a duplicate.
Yup, it has nothing to do with the tstat.
if you don't have any leaking fluid on the passenger side floor, then the heater core remains intact so far.
What you have is a combination of or separately a thing called "wild vents" or the "Heater blend" door is broke. These are both vacuum related.
Do a search for "wild vents". For this one, you may just have a broke vacuum line. Easy places to check first is passenger side of the engine. Find a vac line coming out of firewall. Is it intact? Follow it to the intake manifold as you'll find more lines, 1 going down behind the engine and 1 going back over to the under the battery. Are they intact? Is there a larger union of these lines connected to the intake manifold on the passenger side? Another place is getting on the ground and looking at your front axle, assuming this is 4x4. There are 2 lines that connect to the passenger side of the axle tube. Again if 4x4, look at the passenger frame rail above the axle to find hard lines that take those same vacuum lines to the tcase. Are the intact?
For heater blend door, this is responsible for mixing the hot/cold air. The unit is located under/behind the glove box. The door resides on a pivot made of awesome plastic and this thing degrades/breaks. A little actuator motor rotates it when you adjust the temperature rheostat on the dash. Search "Heater Treater" for a cheap fix. Search YouTube for videos on how to replace it.