Air in heater core

I have a gurgling noise in my heater core once I turn the heat on after the truck sits for along period of time. After the truck runs for a while, and I turn the heat on there is no noise and stays at a constant temp. I have tried to bleed the system with a funnel on the rad cap, heat on full, and on an incline and got some air out, yet the noise persists. I pressure tested the system and it passed so the system is sealed. Does anyone else have this issue with their trucks? I'm at a loss of why mine still does this.

 

Hmmmm. Well i know from experience that even a pressure test will not show all leaks. I would do a test to see if there are any presence of combustion gasses in the cooling system. This will 100% rule out a leaking headgasket and or cracked head/block. This sounds familiar to when the block was cracked on my 94 pickup 22RE. Kept running low on coolant, and i would always hear a gurgling sound where the heater core and over flow was after shutting the engine down. Dont want to be the bearer of bad news hear...

 

Performed the block tests and this is the result. Test fluid was initially a slightly darker shade of blue. Doesn't seem like any gasses are present.

 

Good deal!!! Thats a relief man. If instructions were followed then id say u need to keep bleeding the system. Try parking your truck on an incline so that the radiator is at the highest point. Start vehicle let it get to operating temp, shut off and let cool. Open radiator and fill.

 

the highest point in the system is your heater valve on the firewall, not your radiator, that's why you get trapped air in the system.

install a radiator flush tap at the heater core connection there then fill the hose full and put the cap on it. problem solved.

radiator flush tap available from any auto store http://www.ebay.com/itm/DORMAN-HELP...SAL-/231669957933?hash=item35f09b052d&vxp=mtr

 

Recently bled the system again by elevating the front of the truck. Got quite a few bubbles to come out. For a day or two the heater was silent. Now today after a long drive I decided to turn the heat on. No noise until I slightly revved the engine. Bled it again with more bubbles present. No idea how air is getting into the system other than maybe through my overflow. The rad cap is a brand new oem so I couldn't imagine it leaking.

 

Air trapped at the top of the radiator gets forced into the overflow tank, then when the engine cools coolant in the overflow tank gets sucked back into the radiator. Well, that's how it's supposed to work if you keep coolant in the overflow tank. Eventually, you have no air in the system, but it might take a while. Toyota doesn't say anything about bleeding the air out, so I wouldn't worry too much about it.

 

I've heard that having air in the system may cause the engine to overheat and that's why I've been trying to remedy this problem. However, I think it takes quite a bit to cause an issue. I have the torque app on my phone and can observe my coolant temps and I've been sitting at 190-200 F so everything seems good.

 

I had air in my system not allowing the thermostat to open once when I did water pump and timing belt. I just disconnected the hose on that heater valve at firewall and filled her up with coolant. Did the trick for me.. I wished we had a setup like the 01 passat I just did. Has a bleeder hole in the hose at the firewall for the heater core. Just slip the hose off a little bit to expose the hole, fill with coolant in the tank till it seeps out, then push the hose back on. Done. I'm wondering now if it would work if you just drilled out a little hole on our hose like that.
Edit. Now that I think about it, it probly wouldn't work. As the coolant tank on the passat is the highest point. The radiator is sealed and no cap. You fill it up in the tank at top. So gravity is the way for that. Maybe a separate hose could be used to fill it or something, elevated. But it'd probly be easier to just pop that heater hose off. Idk. Just some thoughts.

 

its easier to just add the radiator flush tap available from any auto store http://www.ebay.com/itm/DORMAN-HELP...SAL-/231669957933?hash=item35f09b052d&vxp=mtr

takes 5 seconds to put in and costs like $3 then you can just unscrew the cap to bleed