Heater core replaced, still no heat!

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remarkablemagic

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So I have a '92 Sunbird SE and it runs good but it's a convertible and just a clunker, but it REALLY needs heat. When I got it the hoses were connected bypassing the heater entirely. So I get a new heater core and have it installed and still no heat!

It does blow just barely lukewarm air now. It seems as if the vents are working right, I mean you get a click when you change the positions and it diverts air where you tell it to go (floor when on "heat", window when on "defrost", etc..), and it also definitely diverts air from a different place when you move the slider from hot to cold.

I have also replaced the thermostat so there is no problem there either. This one I didn't do (I do a lot of my own work but I have a friend who, when I fix his computers, fixes my cars in lieu of payment), but my friend says he saw no sign of crud or lack of flow when he took the two hoses apart.

The only thing that makes any sense, but still also sounds hokey to me, is the guy at the auto parts store said somewhere in the system is a valve that can block the water from entering the heater core? I'd never heard of this, and there seems to be no mention of it at all in the Haynes manual. Is there such a valve? He said it would either be cable operated or perhaps vacuum operated. In any case, if said valve does exist it certainly could be closed, but does it, and if so where is it?

Failing some kind of valve, the only last resort I can see is a full flush of the system (yes I know we should have done it at the time of replacement, but it was a need it now situation). Totally baffling to be sure,m and in a Google search and search of the forum I was unable to find any answers. I found a couple folks with the same problem, but so far as I can tell none of them solved it...
 
Does the temperature gauge read normal? You could have air pockets in the system from replacing the heater core and thermostat.
 
Yeah it reads normal, goes up and down like it should as the thermostat opens and closes.

I found more evidence of it being water valve related though; the heater lines are barely lukewarm when the lines on the other side are hot. I am guessing that the valve is located underneath the intake manifold which makes it a real pain to access, but with the Haynes manual making no mention of it the only hope I have of knowing where stuff is is if I start taking crap apart or find someone with actual experience or a shop manual.
 
I just checked www.napaonline.com to see if they list a heater control valve and came up with nothing. I would disconnect the heater hoses from the ends opposite of the core and try blowing air to see if you have a blockage. Flushing the system with a good cleaner probably wouldnt hurt either.
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I'm absolutely ASTOUNDED by the lack of info on this. I know for a fact the 93-94 models have such a valve, and being so close to the same design I have to assume so does the 92. I can't find the part on any regular auto parts store site either but I find it here.

Worse yet I have encountered at least three instances of guys with this exact same problem in Google searches and no answers on any of their posts. I did see one of those posts (don't know what site) that this guy "heard somewhere" that there is some heater associated problem with the heaters that only a dealership can fix so maybe calling one is in order.

There is nothing in the Haynes manual, and nobody here seems to know. That5 probably qualifies as the most obscure problem I've yet encountered...

It'[s frustrating as hell let me tell you! Thanks though for you guys trying to help. I appreciate anything I can get, and if I get an answer somewhere other than here I will be sure to come back and share it with you all.
 
I am about 90% certain it is not a "gunk" clogging issue, but I did get deep cleaning flush to try in it anyway.

This I find for a '91 model, and, as I understand it, the '91 has the same engine as the 92, the only major change was the first implementation of GM's EFI over the old throttle body injector.

I'm certain there is a valve somewhere as the auto parts store guy also says in cars that new or newer there always is. As I understand it it is a one way valves, just something that prevents flow in one direction.
 
There's gotta be a heater control valve, otherwise your heater would run full-blast all year around.

There's probably a cable going from the heater knob on the dash to the valve, which is probably either on the firewall or behind the dash. Any chance the cable was disconnected when the heater core was replaced (or when the prior owner bypassed the heater core), and never reconnected?
 
I am just about certain there is NOT a switching valve in the line on 93 sunbird. The hoses to the core have always gotten hot on mine when the engine was running. The core on this car flows coolant at all times the engine is running, but the air temp selector draws air from that duct only when moved from cold to hot. This is why when fan speed is on high you can hear change in air sound as you move to hot from cold. It should sound slightly restricted because now air must flow thru core fins rather than around it.

I would just about guarantee u have a restriction in cooling system. I would start by removing both hester hoses from the firewall and have someone start the car (when cold). You should see a healthy flow of coolant out of one hose. Then reattach only that hose to the firewall and you should see a similar or slightly reduced flow out of the other heater core pipe.

Still good flow? the return line may be restricted. try shooting compressed air or garden hose into the return hose with engine off and see if good coolant flow comes out the other end.

There is a little 3 inch molded bypass hose behind the alternator that often clogs on this motor if coolant had been neglected or stop leak had been used in the past. most auto parts stores dont cary this hose but my local chevy dealer parts dept searched it and ordered it from another state for me.
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you said you can hear the "heater blend door actuator" switch from hot to cold but does it open all the way..that is what you should see..and i do see that there is a valve on the 2.0 sunbird..and try to flush out the system just to see what happens..if you took it in like you say they should have flushed it out when they did that..if not, never go there again..I always go to a mom and pop shop if i'm to lazy or will take to long to do it at home..alot of main stream shops like firestone just don't do good work in my opinion and expierence..
 
thats a vacuum tank check valve for $1.28
 
OK, it's been a long time and for a while I gave up on the heat. I actually had the top down most of the summer. Now it's cold again. We did some blowing out of the hoses with air, but it wasn't enough. I bought a flush kit from Prestone. Which heater hose should it attach to? The instructions are clear enough, but in this engine it is quite difficult to trace down all the cooling lines and directions of flow.

The guy who changed the core did not flush the system, but it was a barter thing and I'm not going back to him; he got the hard under dash part done, and at least he spared me that. I'm thinking if I flush it good, the heat should work but it will take a good flush. Someone also suggested after I drain the radiator to run a small about of CLR with the water, but to rinse it out and not let it sit long in the system as prolonged exposure can damage aluminum.

BTW, I had to read damn near the whole chapter in the Haynes manual to find this, but it says too that this particular heater core gets water at all times, that the heater vent door is what controls the heat. I know for a fact this door works, you can hear it move and feel the airflow change.

So in any case, I appreciate the help so far, now if I can find the right place to cut the line and install the "T" then I can flush the system properly.
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Personally I would think if your system was that blocked that the engine would be overheating. Are you sure all the air was bled out after the core was changed? You mention the temperature gauge going up and down, once the car gets to operating temperature it should pretty much not move. Could you have a bad thermostat? Do you have a 195 degree thermostat? The heater hoses are typically two different sizes, the T should fit one of those two only.
 
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melsg5 said:
Personally I would think if your system was that blocked that the engine would be overheating. Are you sure all the air was bled out after the core was changed? You mention the temperature gauge going up and down, once the car gets to operating temperature it should be pretty much not move anymore. Could you have a bad thermostat? Do you have a 195 degree thermostat? The heater hoses are typically two different sizes, the T should fit one of those two only.
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I've been running it without the thermostat since it doesn't heat anyway. What it does is goes way up and then the thermostat opens then it goes down, never really overheats, but at first ti will go to the high end of the scale several times, then once fully warm it stops doing that. I plan to get a new Thermostat and coolant when I flush it fully. It has never actually overheated.

As far as the "T" goes, here are three sizes of "T", so that isn't much help. One hose is larger and one smaller. Which do I want?
 
0.62 in. inlet size, 0.75 in. outlet size, look at the instructions that come with the kit to see whether they want inlet or outlet and decide which hose based on the size.
 
Thank you; you've been a great deal of help. I will let you know how it turns out,
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I don't get it! I have flushed it, blown air through the heater core both ways, blown back into the heater core feed line (to where it came out the radiator), and no matter what I do, no water flows to the heater core inlet line. Still no heat?!?
 
Is the thermostat still missing? If so, try replacing it, the thermostat also creates a differential pressure across the system and that might be all you beed to drive water through the heater core.
 
I have a similar problem with my Bonneville. but have a small crack in the top of the radiator. go I think mine is air locking. going to follow this thread.
 
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