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1/19/16 9:30am - Original Message: '1980 lack luster heater'
DarinM
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Caddo Mills, TX - USA

Vette(s):
1980 Black on Black 4speed 383 Stroker 17x9 rear, 17x8 front with 255-50R-17 Nitto tires OBX Stainless Steel sidepipes DeWitts radiator with dual electric fans

Joined: 9/15/2015
Posts: 38
Last weekend my son and i took a short, cold drive to town and discovered we have a very inadequate amount of heat in the car.After doing several searches in the forums for a problem i'm currently having I've come up with a list of troubleshooting steps of what i've done and what's still left to do so i wanted to run it by the crowd in case i missed something.

Car is 1980 C3 with L48 350. With the car warmed up and the temp gauge barely moving above 100 and the heater on hot and blower wide open. I have plenty of air movement, but not very warm air.

Steps I've already taken
With the car idling in the driveway I can feel the radiator hoses are both warm and both heater hoses are warm and they seem about the same temp.

The radiator is a DeWitts aluminum with stock engine driven fan for now. Plan is to put electric.

I don't know what temp thermostat is currently in it and plan to replace it when i move to the next troubleshooting step. The plan is for a 180 degree thermostat.

There is a vacuum operated valve on the heater hoses hear the firewall that i'm assuming opens and closes the water flow to the heater core. I removed the vacuum hose with the engine running and heat on high, but feel no vacuum in the line going into the firewall. I tried to pull a vacuum on the side of the line going to the valve and it will hold a vacuum leading me to believe the diaphragm in the valve is working. I didn't think to pull a vacuum and check the inside for an increase in heat.

In the cabin, i can hear the flap moving back and forth when i move the temp from cold to hot. But i don't know where the vacuum line goes from the heater core valve into the cabin to make sure it didn't come lose. If there is no vacuum, maybe the valve is staying closed ???

Since i'm planning to add electric fans, i thought while the system is drained, i would pull the heater hoses and try to back flush the heater core.

During the summer the gauge on the dash does run around 190-200 degrees with the A/C running, but during this trip and while idling in the driveway it would barely move above the 100 mark.

Anything else i may have missed ? Might it be worth wile to replace the vacuum valve with a manual one ?

Thanks






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1/19/16 9:43am - Reply: 'Re: 1980 lack luster heater'
manchestershark Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 1901
Heater core plugged? Common problem, cause we don't use them they fill up with gunk. Pull the core and flush it out. Mine works MUCH better after the cleaning.

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1/19/16 9:48am - Reply: 'Re: 1980 lack luster heater'
DarinM
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Caddo Mills, TX - USA

Vette(s):
1980 Black on Black 4speed 383 Stroker 17x9 rear, 17x8 front with 255-50R-17 Nitto tires OBX Stainless Steel sidepipes DeWitts radiator with dual electric fans

Joined: 9/15/2015
Posts: 38
I'm hoping it can be done in the car w/o pulling it ? I was going to pull the hoses from under the hood to backflush. If it needs to be pulled, how hard a job is it ?

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1/19/16 11:50am - Reply: 'Re: 1980 lack luster heater'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 872
It's a heck of a lot easier to pull the hoses off the engine than to pull the core, I think.  I'd back flush it through the hoses.  I'd also go back and see if you get warm air in the cockpit when you pull a vacuum on the valve.  If you do, then you don't need to back flush, just find out why there is no vacuum to the valve.

I have a 180* thermostat with my DeWitts, and it rarely goes above that except in the summer with the a/c on.  In fact, I'm wondering if I mistakenly put a 160* thermostat in it.  Hell of a radiator.


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1/20/16 10:00am - Reply: 'Re: 1980 lack luster heater'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
hi    I don't know how  much  water pressure have   but keep it low to flush heater core  use only water  if something is  in core  it will come out  just use water  not high pressure and check heater control valve  rs of engine   by exhaust manifold   make sure this is opening    take your time  let us  know     dwa175

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1/20/16 11:16am - Reply: 'Re: 1980 lack luster heater'
crossfire1982
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Cramerton, NC - USA

Vette(s):
black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion

Joined: 8/22/2006
Posts: 1094
Without knowing your history with  the car this post may be useless but there is another possibility.  It is fairly common to install a manual water cutoff valve in the water lines going to the heater core. This is done to completely shut off the hot water to the core during summer.  Mine are hidden in the lower part of the hose under the car and out of sight. If you haven't already checked, make sure there isn't a valve somewhere that is closed and preventing hot water from getting to the core.

The vacuum line that goes to the factory vacuum water shut off on my 82 comes through a 3 port grommet in the firewall near the distributor and feeds from a plastic valve mounted under the dash just above the glove box.  I had to replace some of those vacuum lines to get my factory valve to function properly.  The plastic valve gets its vacuum from a "T" in the line near the brake booster, yours may be different.  Hope this makes sense and helps you troubleshoot.

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1/20/16 11:38am - Reply: 'Re: 1980 lack luster heater'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 872
I have a manual shutoff in my heater hose as well because the 72 didn't have the vacuum valve.  Heater core was always hot.

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1/20/16 12:01pm - Reply: 'Re: 1980 lack luster heater'
DarinM
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Caddo Mills, TX - USA

Vette(s):
1980 Black on Black 4speed 383 Stroker 17x9 rear, 17x8 front with 255-50R-17 Nitto tires OBX Stainless Steel sidepipes DeWitts radiator with dual electric fans

Joined: 9/15/2015
Posts: 38
Thanks All for the suggestions. I did check for a manual valve inline and there are none there. now that i understand when vacuum should be there and what it does it will help to troubleshoot. I've been called to go out of town for work, so it will be a couple weeks before i can report back, but it's now top of my to-do list ! I'll certainly respond once i get this done !

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7/18/16 11:21pm - Reply: 'Re: 1980 lack luster heater'
jim in oregon
Former Member
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Milwaukie, OR - USA

Vette(s):
'78 Silver Anniversary T Top coupe,58k orig miles. THM350 auto, 350 L48, JBM headers,Oyster White interior,.as of Nov '15 in process of painting.

Joined: 10/19/2015
Posts: 71
DarinM said: Thanks All for the suggestions. I did check for a manual valve inline and there are none there. now that i understand when vacuum should be there and what it does it will help to troubleshoot. I've been called to go out of town for work, so it will be a couple weeks before i can report back, but it's now top of my to-do list ! I'll certainly respond once i get this done !



Well..IF you have no vacuum to the in line solenoid in the heater hose..It is quite possibly the temp control cable that runs R/S of console from the master hvac mechanism to a BYPASS water shutoff valve that resides behind the glove box.The bypass does several things..When you switch to cold with A/C OFF it transitions mechanically AND vacuum wise to supply vacuum to shut the solenoid in the heater hose And..OPEN air duct vents for the other options on hvac..that bypass switch when temp is moved from OFF/COLD opens the hot water that provides def/heat..or just vent from outside.The cable has a turnbuckle that is used to get the adjustments so the temp control lever changes the MODE for the hvac..
the bypass is accessible-visible IF you remove 6 phillips head screws and the lamp-socket after opening glove box..The cable access is acquired by removing the R/S  console panel..Jim
here's a good diagram of what does what..
 


|UPDATED|7/18/2016 9:21:54 PM (AZT)|/UPDATED|


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