Running hot-Heater blows cold? Gurgling sounds at start up

[Cabrito]

I got most of what I need using the search but still have questions.

Okay so I think I need to Burp the system because I hear the rushing water sound when I start up. This has been going on for some time.
Now there is a new twist. A few weeks ago while sitting in bumper to bumper traffic after about 5 minutes it started to run real hot on the temp gauge. When I turn on the heater to help cool the engine it started blowing cool air. The rear heater blows hot but the front blows cool.
After a very stressful 15 or20 minutes in the heavy traffic with no way to escape the traffic finally clears and the engine revs up a little the heater starts blowing hot (Like it should) Note to self: Burp the thing when you get a chance.
So today two weeks later on the way to get my oil change while sitting in traffic I decide to check the heater – No dice – it’s blowing cool air. As soon as I am up on the freeway it’s blowing nice and hot. Same on the city streets. Cool at the stop light but heats up when I start driving.
Currently it’s in the shop and they are checking it out. I asked about Burping the system and they looked at me like I was from Mars.
Any input would be great!
Thanks,
Michael

 

[trucruiser]

I have seen this happen with a low coolant level, or a sticking thermostat.

 

[another line]

Could someone explain how to burp the system? My 85 60 makes that gurgaling sound when I start it also.

Thanks

 

[Cabrito]

Some results and Burp how to

So the shop found my coolant level low and filled it (Doh! Why didn't I check this?). They checked all the heater components and found everything working. I am guessing that since my coolant was low there was air in the system which was affecting my heater. It now blows hot at idle like it should, and I have not noticed the rushing/gurgling water sound. They did however find moisture in my oil filler cap. Oh Crap! They say possible blown head gasket. I will monitor this situation.

Here is what I find using the search feature for “Burping” –
Burping the coolant system is easy. W/ the engine cold open the radiator cap, position the truck so that the radiator is higher than the back end (front end on ramps or even a curb should do), start the enging and get the coolant up to temp so that the thermostat opens, rev the engine and watch for the coolant level to drop in the top of the radiator - you'll probably get a "burp" as the air works it way out of the radiator. Put the cap back on - make sure you have coolant in the resevior and you're done.