heater not working

[boxerjl2]

Hello I have a 74 Chevy k10 383 stroker and my heater won't work IV
The blower is working fine. IV burped the cooling system (front end elevated).. and the
only time it will heat up is when the radiator cap is off..temp gauge stays at 190
 When its warmed up so no over heating problems the heater code was replaced a
A year ago.. waterpump and thermo was replaced last summer.. IV tried googjy and the search option and mostly all I see is pole heaters not working at all
Has anyone had this problem? It doesn't make since to me but this is
also my first old truck

Thanks in advance

[Irish_Alley]

are the hoses getting warm that lead to the heater core? did you happen to get a failsafe  thermostat?

[Greybeard]

Check the cable connection to the heater valve on the firewall. Make certain it's opening. It could be plugged from age. Easy fix, remove it, put a boiler valve in (for the time being anyway) on two 1/2" nipples. Turn it off when it warms up. Then put a good heater valve in when it's warm or however you feel is easiest. It's been sub zero here, that's why I say this. If the cable broke but the valve still works just open it by hand till you can get a new cable.

[boxerjl2]

Irish.. yes the hoses are hot the heater works but only when the radiator cap is off.. and. Not sure about the thermostat.. I just got a normal 9ne from what I know Idk what a failsafe one is

And thanks for the info grey but my cables are working the glovebox is still off from the heater core change and can see them working

My heater wasn't working so I googled it and that's when I burped the coolant and my heater was blowing super warm so I put the cap back on and drove about a block and then it was just blowing air

[Irish_Alley]

it sounds like you still have air. dont worry about the fail-safe, they are twice as much as a normal t stat. and they will fail open instead of the normal ones that will fail shut causing you to over heat. i normally will use the upper hose as a pump when im filling up the rad. fill it almost full and pump the upper hose, never one have i had to lift the front end or had air stuck in the system

[Greybeard]

Irish.. yes the hoses are hot the heater works but only when the radiator cap is off.. and. Not sure about the thermostat.. I just got a normal 9ne from what I know Idk what a failsafe one is

And thanks for the info grey but my cables are working the glovebox is still off from the heater core change and can see them working

My heater wasn't working so I googled it and that's when I burped the coolant and my heater was blowing super warm so I put the cap back on and drove about a block and then it was just blowing air

Sorry, glossed over the heating up part...   

Maybe try just pulling the hose off the upper heater attachment point, hold it up in the air and manually fill the core? Maybe somehow got some chunks of silicone or gasket sealer in it?

Last resort, blow garden hose water through it (very low pressure) and the valve to eliminate any possibility of obstruction? 

I might be learning things here myself, I have never heard of air ever being a problem in an old chevy system... But I'm also not saying it couldn't happen...

[boxerjl2]

I'm not sure how it could be air but Idk its been a total of about 45 mins of trying to burp it guess I could try again..
the first time I burped it it dropped the radiator by about Half way so I refilled it and let it run for about another ten minutes and IV done it 3x since then with no drop in coolant

[Greybeard]

Back in the day I used to flush and fill all my vehicles cooling systems yearly, I never remember ever having any problems with any of them retaining air. The 345 binder engine on the other hand....yes.

GM products from the early seventies have been pretty well engineered in that department. Until the metrics showed up, then everything went to the septic tank. Common sense was thrown out to meet EPA, fuel mandates and CARB requirements and other guidelines, and now just looking in an engine compartment seems to break things. 

[VileZambonie]

Ensure the upper radiator hose is getting hot. If not replace the T-stat and don't use a fail safe they're crap. Run a 195°

[bd]

I'm not sure how it could be air but Idk its been a total of about 45 mins of trying to burp it guess I could try again..
the first time I burped it it dropped the radiator by about Half way so I refilled it and let it run for about another ten minutes and IV done it 3x since then with no drop in coolant

Use this method to make sure the cooling system is completely full...
Loosen the radiator cap to the safety stop; but don't remove it.  Saturate a shop rag with plain water.  Have a garden hose handy that will reach the radiator filler neck.  Run the engine to operating temperature (upper radiator hose HOT).  Set the engine running on the high step of the choke fast idle cam (1,200+ RPM), turn the garden hose on, grab the radiator cap with the water soaked rag, and while running cold water from the garden hose over the rag and your hand to keep from being scalded, carefully remove the cap being mindful of near boiling coolant.  With the engine still on high idle, top off the radiator and install the cap tight.  Now, bring the engine back to normal curb idle RPM.  Are both heater hoses hot where they connect to the core?

[boxerjl2]

Ill try that and yes all hoses are hot.. I have a small leak on the thermostat housing. Could that somehow suck air in?

[bd]

Ill try that and yes all hoses are hot.. I have a small leak on the thermostat housing. Could that somehow suck air in?

No

[boxerjl2]

I tried your message twice with no drop in coolant.. I have gone all the way up to the bottom of the filler neck... I also tried heating it up with the radiator cap off and the heater was blowing hot 2 minutes after putting the cap back on the heater stopped working

[Irish_Alley]

to my knowledge the cap only does three things, one is cap the system off the other is hold the coolant under pressure. for every lb of pressure it raises the boiling point of coolant by 3°. and lets the rad suck coolant back from the over flow. is your truck sitting at 190° both with and with out the cap in place?

[VileZambonie]

How are your heater hoses routed? Pics