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  #1 (permalink)  
Old 09-02-2006, 06:21 PM
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no heater

i have 78 full size chevy truck that will not put out any heat on the heater. i put a new heater core in it i put a new thermostat 195 degree,high flow water pump,radiator and i even put a 4 blade fan and 7lb radiator cap on and still in cold weather there is no heat the motor runs 200 degrees the heater core is not stopped up in anyway. i even tried blocking airflow through the front of the radiator and boiled it over and still no heat i have also took the duct work out and made sure it flowed .the cab is well insulated besides i got a buddy whose truck has holes in the floor and you can almost cook off his heater. the last thing i done was rerout the heater hoses from intake to radiator from water pump to intake from water pump to radiator so icant think of anything else but try a restricter of some sort on the return hose.

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Old 09-02-2006, 06:29 PM
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You got me confused about how you routed your heater hoses.....they are supposed to go intake to heater core and waterpump to heater core.
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Old 09-02-2006, 06:33 PM
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my radiator has a water inlet for a heater hose just below the cap i have already had it from water pump to heater core to intake and there was no difference
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Old 09-02-2006, 07:38 PM
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Run the engine up to temperature, turn the heater control to full hot. Feel the heater hoses, both should be hot if water is running through the heater core.

If one hose is cold, then you have a problem with the water supply. Not sure if GM used a vacuum valve on that body or not.

If both hoses are hot, then the problem is likely with the blend door in the dash. Could be a linkage broken and keeping it on outside air. Had a small plastic lever break on my '80 Chevy that resulted in no temperature control.
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Old 09-02-2006, 07:47 PM
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ive already checked that heater hoses are both hot door works fine. shut its cold open its a little bit warm, i know sounds crazy but everything working but no heat or at least not enough
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Old 09-02-2006, 07:53 PM
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In 78, chevy pu's ran the water from the manifold by the thermostat to the heater core and returned it to the radiator below the filler neck. Plug the fitting at the radiator and put the return to the waterpump. Use a restricted 1/4 inch id fitting at the manifold outlet. there is no water control valve in the system. Temp is controlled by vacumm and cable operated doors in the heaterbox. If the doors don't shift with the controls, most likely the problem is the vac control switch behind the dash lever controls.
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Old 09-02-2006, 08:07 PM
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Quote:
Originally Posted by 61bone
In 78, chevy pu's ran the water from the manifold by the thermostat to the heater core and returned it to the radiator below the filler neck. Plug the fitting at the radiator and put the return to the waterpump. Use a restricted 1/4 inch id fitting at the manifold outlet. there is no water control valve in the system. Temp is controlled by vacumm and cable operated doors in the heaterbox. If the doors don't shift with the controls, most likely the problem is the vac control switch behind the dash lever controls.

"In 78, chevy pu's ran the water from the manifold by the thermostat to the heater core and returned it to the radiator below the filler neck"
This is true, as is my 77 chevy. Not sure why you say to move the radiator end to the water pump. Mine is "intake to heater, heater to radiator.

If both hoses are HOT, you may have a partially plugged core or like others have said, the blend doors could be messed up. You can get HOT hoses and still have a clogged core. It doesn't take much flow to get hot hoses, but takes lots more flow to heat the cab. When I suspect a clogged or partially clogged core, I remove both hoses and put the garden hose on one and slowly begin to flush it out. You'd be amazed at how much crap will come out.

Question, how much air movement do you have with the fan on HI? Reason I ask is the heater and A/C cores can get covered in dust/dog hair/girlfriend hair and all kinds of crap. Finally split the housing on mine last year when my air flow almost stopped and found a thick layer of 30 years of crap covering the A/C core.

Mark
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Old 09-02-2006, 08:09 PM
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Non AC trucks had no vacuum controls

Could also check for debris in the air intake

The heater in my 79 don't work too well in the winter either
My 78 would cook me right out in just a few minutes
neither of these had factory air

Bryan
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Old 09-03-2006, 08:25 AM
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this is a non ac truck are you saying there are now vacuum control
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Old 09-03-2006, 08:29 AM
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You have either got a restriction to hot water flow somewhere or the airflow through you heater core is blocked somehow, or your heater core is stopped up.
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Old 09-03-2006, 08:36 AM
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i know what your talking about. the radiator i got has a 5/8 water inlet 3 inches below on the radiator cap side
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Old 09-03-2006, 09:42 AM
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A/C equiped trucks did NOT have a heater shutoff valve in either hose.

Mark
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Old 09-03-2006, 10:26 AM
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Might try this to check flow

Should be a 5/8" hose from the intake manifold to the bottom inlet to the heater core.
Should be a 3/4" hose from the top outlet of the heater core to Radiator

Drain radiator to just below the level of the heater hose entrance to the radiator---start truck---check the flow coming from the heater,

If it is flowing freely it is doubtful that there is a blockage in the system.
This can be seen with the radiator cap removed.
If there is no flow there is a blockage somewhere (hose, heater core, intake manifold outlet)

This is not regulated by the thermostat so it is not necessary to wait for the truck to warm up.

Bryan
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Old 09-03-2006, 10:44 AM
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Quote:
Originally Posted by Bryan59EC
Might try this to check flow

Should be a 5/8" hose from the intake manifold to the bottom inlet to the heater core.
Should be a 3/4" hose from the top outlet of the heater core to Radiator

Drain radiator to just below the level of the heater hose entrance to the radiator---start truck---check the flow coming from the heater,

If it is flowing freely it is doubtful that there is a blockage in the system.
This can be seen with the radiator cap removed.
If there is no flow there is a blockage somewhere (hose, heater core, intake manifold outlet)

This is not regulated by the thermostat so it is not necessary to wait for the truck to warm up.

Bryan
Excellent suggestion Bryan! Mine roars like crazy when its running! That will get that figured out in no time.

Mark
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Old 09-03-2006, 11:20 AM
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believe it or not ive done that and it flows real good
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