no flow to heater core hoses

[jimbalaya]

I am trying to diagnose why my heater has worked sporadically since i replaced the radiator a few months ago. I have done a lot of reading from previous threads on this site and am wondering if no water flowing in/out of the two heater core hoses means definitely that the HCV is stuck closed or that heater core is clogged. It seems oddly coincidental that this began right after radiator replacement.

here is what I have confirmed so far about heating system:

• temp gauge reaches normal operating temp after a few minutes of driving and stays pegged just below the halfway mark;
• top radiator hose does not have flow and become hot and firm until after the engine reaches normal operating temp [which should mean that thermostat is working correctly];
• both heater core hoses do not get hot with heater control on and engine at normal operating temp; nor do i feel any flow as i can pinch closed with fingers;
• blend door appears to be working correctly

let me know what you guys think - thanks in advance.

 

[Bobmbx]

I suspect the HCV. One way to check the core is to remove the heater hoses from the firewall and install a jumper between the supply and return hoses. If they get hot this way, but not when hooked to the core, your core is blocked.

Before you do all that, though, just manipulate the HCV by hand with the engine running and hot. If it works, verify you have vacuum at the HCV, and that the vacuum hose is pushed all the way on the HCV actuator nipple.

 

[crunchie_frog]

Or, just pull the heater control valve (just hoses in and out to remove) and see if it is open without vacuum and closes with vacuum.

 

[jimbalaya]

I suspect the HCV. One way to check the core is to remove the heater hoses from the firewall and install a jumper between the supply and return hoses. If they get hot this way, but not when hooked to the core, your core is blocked.

Before you do all that, though, just manipulate the HCV by hand with the engine running and hot. If it works, verify you have vacuum at the HCV, and that the vacuum hose is pushed all the way on the HCV actuator nipple.

Thanks. I may have to try the heater core bypass first since the HCV on my 97 XLT SOHC is between the fan and the pulley/belt system - looks hard to get to without removing the air intake and the upper radiator hose. also, it is vacuum controlled but i do not see any exterior movable parts on my HCV like i have in photos of other HCV's, so i would not be able to manipulate it manually. (I guess i could pull off the vacuum hose but doesn't that [vacuum] pull the valve open [to allow flow]?

 

[jimbalaya]

Or, just pull the heater control valve (just hoses in and out to remove) and see if it is open without vacuum and closes with vacuum.

Thanks for your suggestion. Will try that if heater core bypass test fails to 'solve' the problem. (see my other post about HCV is not easily accessible near the firewall like in other configurations.)

 

[rb142]

You may just have air trapped in the system.

 

[jimbalaya]

You may just have air trapped in the system.

thanks. that's what i was thinking because it seems too coincidental that right after i replace the radiator the HCV suddenly goes bad or the heater core suddenly blocks up.

what's the best/easiest way to release any trapped air? I have read many posts on this site about that and here are a few methods i recall:

• get your front end up so that the radiator is the highest component of your cooling/heating system and run the motor for awhile [i forget if you leave the radiator cap on, off or loose];
• loosen the 'release valve' [but I'm not sure if my model has one];
• just put on radiator cap to first locking position but not all the way to the full lock position - and then run engine for awhile;

my fluid has always full in radiator each time i check it for the last few months since changing the radiator.

 

[RomeovilleIL]

Default position of HCV without vacuum is open so a lack of vacuum hose should have no effect on heater function (the valve is closed when a/c is turned on). If the valve is stuck closed it is almost always because of crud like rust or leakstop. They have a habit of getting plugged up along with the heater core when the cooling system is flushed. The suggestion of hooking the two heater hoses together with a simple piece of pipe (ie creating a bypass) is a good way to test the system.

How to get air out of heater core: The passenger side hose is the intake, the driver side is the outlet. Disconnect the outlet side hose from the pipe (not at the core) and hold up. Slowly pour water or 50/50 mix with a funnel into the hose and keep elevated until the hose and core are full. Tape the hose to the hood to keep it elevated, then bounce the front end a few times. Let sit for maybe 5-10 minutes and check if still full. If not, add more liquid and repeat. Usually gets done in one or two tries. Re-attached the hose to pipe.

If the core is plugged, it's not difficult to backflush with water and compressed air. Disconnect outlet side same as above. Disconnect inlet side also at pipe and place end into an empty 2-Liter bottle. You want the hose to be pointed downward so gravity will allow any fluids in the core to flow down into the bottle. There needs to be some gap for air to escape from the bottle, so do not tape the bottle to the hose. Pour water (not 50/50) into the outlet hose to fill the core. If it doesn't immediately run out of the inlet hose into the bottle, then there is a plug. Gently blowing compressed air into the outlet hose will push the water and air through the core along with any junk stuck in the core (hang on to the bottle and hose you might have a water rocket flying across the garage). Flush a few times until the water flows through freely when poured in the outlet hose. Don't be super agressive with the air pressure as we don't want to damage the core (30-40 psi is plenty). Once everything is cleared out, rehook the inlet hose to the pipe. Refill and burp air from core as described earlier.

 

[jimbalaya]

How to get air out of heater core: The passenger side hose is the intake, the driver side is the outlet.

Thanks Romeo, for the comprehensive response and taking the time to provide the all of the info. One quick question about the intake vs. outlet heater core hose: My HCV is on the driver side hose - I thought whichever hose the HCV is on is the intake?

(the driver side hose travels down to the middle/front engine area and appears to enter near the water pump; the passenger side hose travels horizontally and connects with the thermostat housing)

 

[jimbalaya]

UPDATE: well, the heater core is definitely not plugged. I disconnected both hoses and poured water into the intake hose and clean liquid flowed from the outlet hose.

This seems to lead to the only remaining possibility, which is that the HCV is stuck closed [because there is no flow to the heater core and the hoses never get warm/hot after engine warms ups and temp gauge goes from cold to showing engine is at normal operating temp].

-------------------
UPDATE 01-02-15: the heater has been working ever since i poured water through it as stated above; since i simply poured water into the outtake hose and it flowed freely out through the intake hose, i assumed the heater core was not plugged - but it seems to have been or there must have been air in the system as "rb142" suggested.

only issue now is that although the heater always works now, it takes several minutes to begin working once i turn on, even though I wait 10-15 after engine starts/driving before i even turn heater on. if anyone has any idea on the cause of this, let me know.