I did a search, but I think I have a different scenario. Lately, (and this just started) whenever I start my truck after it has sat overnight, I hear a gurgling sound from the heater core whenever I rev the engine a little, and then it goes away after about a minute of the truck running. It still puts out hot heat ( and we have had temps -10 below so far). This summer I had a new timing chain and cover put on, new upper manifold gasket, and a new water pump and a full radiator /coolant flush that the dealer used a machine to flush it with.
I am also smelling antifreeze sometimes, and am finding small drops on the garage floor but cannot find where it is coming from. What is going on, with the heater core gurgle at startup? Oh yeah, heater core is not leaking inside. Thanks!

 

Gurgle means air in the system = not enough coolant. So you most likely have a leak.

Seeing where at the coolant on the garage floor should help you see what area of the engine it's leaking from. Lay down some fresh cardboard to really help, just make sure it wasn't raining when you pulled in lol.

I just changed mine and I had a trickle leak at the join of the upper heater core hose (new clamps fixed it no worries).

 

the leak is letting coolant out and air in. the gurgle is just the air. fix the leak.

 

If you did a search then you would have found many other threads that address this issue.

 

regarding extremely cold temps.. i've seen mine leak a couple times in cold weather. maybe the waterpump seal shrinks up a little...

 

I know theres a recient thread or two where I mentioned this exact same problem....for me it was leaky softplug between engine and tranny...fixed it with stopleak...btw you could have a small leak in heatercore and not notice it because the base of the carpet is waterproof rubber...under that is a 1/2 inch of insulation....mine was soaked from a leak at the firewall I.ve still yet to find but I only noticed it because I pulled up the carpet to run speaker wire and amps.

 

IMO f you are smelling antifreeze in the cab then you most likely need a new heater core.

 

I'd say you have a leak somewhere that's for certain. I have a 97 that does this. I've read before that it had something to do with the heater core placement. Mine does the same thing. I read that if you park it on an uphill angle, take the radiator cap off and start it up and then add coolant to fill the entire system. I did try this, but my radiator was full to the top and never went down :/ My heater seems to work fine. I have also read that sometimes it's crud in the heater core making this noise, I'm guessing that's what makes mine gurgle.

 

I would try running a bottle of Bar's stopleak or something similar for a week or so, then just flush the coolant system to clean out any debris you have in the system. Just don't forget the drain plugs in the sides of the block, near/behind the motor mounts.

 

The gurgle is air. for some reason you have an air pocket in your heater core....did you do the park on an angle thing and check coolant leavel with the heater on full blast and wait till the engine reaches full temp like your supposed to? if so your coolant level has to be slowly dropping because air is being introduced into the system somewhere.