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73-87 Chevy _ GMC Trucks => Interior & Equipment => Heating, Ventilation & Air Conditioning (HVAC) => Topic started by: boxerjl2 on January 29, 2014, 11:23:14 pm
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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
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are the hoses getting warm that lead to the heater core? did you happen to get a failsafe thermostat?
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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.
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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
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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
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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...
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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
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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.
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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°
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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?
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Ill try that and yes all hoses are hot.. I have a small leak on the thermostat housing. Could that somehow suck air in?
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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
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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
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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?
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How are your heater hoses routed? Pics
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Yes the truck stays at 190 once heated..
Ill get pics of the engine bay
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Here it is.. this is how it was hooked up when I bought it
Bottom hose is hooked to water pump and top hose is hooked to the intake manifold
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ok maybe its just my set up but i have the pressure side your top hose in the intake and that looks right but the return is hooked up to the rad right underneath the over flow
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ok after looking it up it seams it can go either way. but the top is supply and the bottom is suction so in theory you can have a air bubble get trapped in the core
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Ok so the water pump shud be hooked to the top
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I probably mixed up the hoses when I replaced the water pump last summer
Would explain why it worked perfect last winter
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Ok so the water pump shud be hooked to the top
I probably mixed up the hoses when I replaced the water pump last summer
Would explain why it worked perfect last winter
The heater supply exits the 5/8" bib in the intake and returns through the 3/4" bib in the water pump. The heater core similarly has 5/8" In and 3/4" Out bibs. Connect the hoses accordingly.
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Ill have to check that out thank you for your help
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As far as I can tell from what u said the intake bib is the supply and the top of core is supply so I have it hooked up correctly from what u said
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yes, the water pump bib and (if you had one) the rad bib are the same size and both are return. if you had the one in the rad you could just look into the rad and see how well it was flowing. i also want to say (just me thinking bd or someone verify) but some water pumps also have ports on the driver's side these would be supply's and the ones on the passengers side are returns
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This water pump only has one bib that I can see.. I still don't understand. Why its only working with cap off.. cud I have too much coolant?
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to me, that makes no sense. I can't think of any reason why the cap would cause the coolant to stop circulating through the core. Your hose bib on the radiator is not in the neck is it? Shouldn't be.
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the only thing i can think of is the cap allows pressure to build up in the core restricting flow threw the core. the only thing i can think about that would cause a restriction would be air. try reversing the connections on the heater core. like put the water pump (return) to the upper connection (supply) in my head this would force anything (air) up and out. its easier to get air to go up then down.
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you said both heater hoses are hot to the touch which would mean the hot coolant is passing through the heater core if I'm not mistaken. could it be your switch in the cab is set to cold and not hot? also making sure ur switches work, from how my truck works you slide the switch over and it moves a flap in the heater allowing hot air to pass through from the fan blowing through the heater core. when you slide your switch over can you hear the flaps moving? maybe they broke in the "cold" position
Sent from my iPhone using Tapatalk
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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
OK, you see the cables working, that doesn't necessarily mean they moving what they are attached to. There is a small valve that controls the coolant flow through the core this is easy to see if it's still there, the flap door inside the dash may be a bit tougher to but a flashlight helps there. The cooling/heater systems on these old trucks are about as simple as it gets when there is no A/C to deal with.
It still makes no sense why it would warm up with the cap off and not on. The cap has no bearing on the way the coolant circulates. All it does is keep the pressure in the system to raise the boiling point.
I still suggest draining about half the fluid out and disconnecting both hoses to the core at the engine and using garden hose pressure (unless you have 60psi water pressure that is) and blow water through it from both directions. Start with a slow stream to see if it is open, then keep increasing the pressure to see if there is a point where it doesn't want to let as much out as there is going in. Be careful and don't over pressurize because they (the core) are only capable of handling about 20psi. The r/cap should be about 14 psi. Some are as low as 7 psi. If a good solid stream is flowing (not shooting!) out the end about three inches then it's good to go. It needs to fill the hose diameter with the hose nearly level or below the point of attachment to the core.
However, if this pans out it has to be inside the ductwork. Pull the fan out and see if the face of the coil isn't plugged with crud. Pull the coil off and look and make doubly certain the doors are all opening and closing completely. On my truck they make a solid thunking noise in both directions as they move overcenter. One other question...it wasn't at one time a truck cab that had a/c was it? If so there is a air valve on the passenger side where non-a/c trucks usually have a manual vent. If you have the manual vent nothing to worry about. Otherwise, if that fresh-air-bypass valve is open it lets cold air in from the outside, it's supposed to close (or open, I don't remember which) with vacuum in concert with the a/c or heat (again...don't remember which).
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I've never seen a coolant valve on these trucks. I would look towards the heater controls and doors within the heater box. Once I had a LPG powered truck and the heater hoses were connected like yours are one to the intake and the other to the water pump and it didn't work that way. It had to return into the radiator just below the cap, so from the intake to the heater core back to the radiator.
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chevy2500hd
Yup, I admitted my mistake and realized I was thinking of some work trucks we used at work. I went and refreshed my rotten memory on my truck outside and saw my embarrassment. D'OH! being old and away from some things for a while is a tough pill to swallow at times. I do not and want not to give false information. If I believe something is true in the future I will give that information as such..a belief. But some things were home built back in those days just as today so...
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yes some did put shut offs on the lines just because some of our trucks the fan blows all the time. so they would put controllers or valves just so they wont be blowing hot air into the cab in the summer
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I keep wondering if the problem could be a collapsed hose going to or coming from the heater core. Installing the radiator cap is causing a pressure change and something in the system isn't reacting correctly.
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You don't have compression going into your coolant system do you? Intake or head gasket maybe.
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I keep wondering if the problem could be a collapsed hose going to or coming from the heater core. Installing the radiator cap is causing a pressure change and something in the system isn't reacting correctly.
I would agree with this too. The heater core as far I know (that is disclaimer) is a straight through system with no check valves or anything. But as in all liquid systems the flow has to be allowed to go somewhere for it to come from somewhere. The fact it's cooling off indicates that the flow is stopping or the damper door is closing (or moving out of the heat position at any rate).
If the coolant line are hooked up correctly there is a very real possibility I guess (another disclaimer) that the lines could be collapsing as DnStClr suggests. The return line should be connected to the water pump after all which I assume (disclaimer) would cause somewhat of a suction. The cheap attempt to fix this would be to buy quality hose from a reputable source like Napa. (I always say Napa not because I like them but because they are one of the only two auto parts stores in my town. Oreilly's being the other so Napa, as far as I'm concerned, has the better supplies, Oreilly's is where I usually get my stuff from though because they are less expensive).
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every picture i see has the supply (intake) hose in the bottom. and the return (water pump or rad) on top. but he hasnt been on in a month so maybe he fixed it
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God, this thread goes on and on!
Yeah, Irish_Alley, we haven't heard from the OP in a while, so maybe he's fixed, but just in case:
From the picture, the hoses to the heater core are hooked up backwards. This is confirmed by 1) my own truck, which works fine, thank you; and 2) the 1973-1978 Chevy Light Truck Service Manual.
The bottom connection to the heater core is a smaller hose connection. It is the supply connection into the heater core. It must be connected to a hose nipple on the intake manifold.
The top connection to the heater core is a larger hose connection. It is the return connection from the heater core. It is connected to the water pump nipple, or to a nipple in the top of the radiator reservoir.
The purpose of this is to fill the heater core up from the bottom, so air is forced out the top and back to the system, preventing air from being trapped in the heater core. Air wants to go up in water, and you want the air out, so up has to be the out direction.
Before you do anything else, re-connect the hoses properly. You may have other problems, but without the hoses connected properly, who knows what is happening in there.