Topic: Flush or No Flush?
in Forum: C3 Cooling and Heating Systems
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Former Member
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Chicago, IL - USA
Joined: 11/30/2007
Posts: 37
Vette(s): 1976 L48 T-top, Automatic, ps,pb,a/c, Everything stock. Good car in great shape.
I just bought a 1976 and the heat isn't working. So far, I've replaced the thermostat and haven't gotten much further. Does anyone think that flushing out and cleaning the system might help? I'm worried that there may be junk or rust clogging the heater core or some of the hoses...
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Former Member
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Cramerton, NC - USA
Joined: 8/22/2006
Posts: 1094
Vette(s): black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion
Check along the heater hoses to see if the previous owner may have installed manual cutoffs on the hoses (a common practice). Check all the way along each hose to the heater core connection under the car.
Former Member
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Chicago, IL - USA
Joined: 11/30/2007
Posts: 37
Vette(s): 1976 L48 T-top, Automatic, ps,pb,a/c, Everything stock. Good car in great shape.
ok...cool. Let's pretend that I didn't know where or what the heater hoses looked like...do they come out of the water pump? There are two right?
Lifetime MemberModerator
Moses Lake, WA - USA
Joined: 4/16/2005
Posts: 2134
Vette(s): 1976 L48 4-spd, Mahogany Metalic exterior, Buckskin interior 350ci/350hp, 3rd owner, fiberglass spring, 255/50-16's Torq-Thrust II
One comes out the side of the water pump. The fitting in the water pump should stick out about 1-1/2" directing the hose towards the A-arm on the right side of the vette and pass under the A/C compressor. That hose is 3/4" id. The other hose comes out of the right side of intake manifold between the thermostat and head. Its a 5/8" id hose and if the clip is still on the fender then they are secured there. In line on one of the hoses near the clip is the factory shut off valve. It should have a small vac line attached to it.
Lots of folks do install gate valves somewhere in these lines (you have to do both lines to do any good). It will be a screw in "T" handle type valve that opens and closes to allow for water flow.
Most put them where you can get to them but some do put them up under the A/C box. DO NOT grab them if the car is hot! Wait for it to cool down to turn them.
Most put them where you can get to them but some do put them up under the A/C box. DO NOT grab them if the car is hot! Wait for it to cool down to turn them.
Check to make sure the hose is connected to the heater core. Some people who may have had a leak in the core just bypass it.
Also, check your heater control valve and switches and make sure they're working too.
I flush mine every year (I can't help that I'm anal)
If You've check for manual shutoff valves and your control valve is working properly, fell the hoses going in and out of the heater core. If the outlet (to water pump) is noticeably cooler that the inlet (from engine block) then the core could be plugged. If they are both hot you may have a blendoor problem. Terry
Former Member
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Chicago, IL - USA
Joined: 11/30/2007
Posts: 37
Vette(s): 1976 L48 T-top, Automatic, ps,pb,a/c, Everything stock. Good car in great shape.
OK...so I've figured out that the hoses running into the heater core
aren't hot when the engine is at temp. So there's a flow issue
somewhere. I also noticed that the hose running from the engine
block, I believe, goes into the A/C box and is attached by a vacuum
actuator valve that appears to have the vacuum line cut. Is it
typical to have this valve in the line, and if so, where can I trace
to where the hose should go to supply the vacuum? Will this cause the
flow problem to the system? Last question...what causes the actuation
to happen to the valve in the water loop?
aren't hot when the engine is at temp. So there's a flow issue
somewhere. I also noticed that the hose running from the engine
block, I believe, goes into the A/C box and is attached by a vacuum
actuator valve that appears to have the vacuum line cut. Is it
typical to have this valve in the line, and if so, where can I trace
to where the hose should go to supply the vacuum? Will this cause the
flow problem to the system? Last question...what causes the actuation
to happen to the valve in the water loop?
Former Member
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Chicago, IL - USA
Joined: 11/30/2007
Posts: 37
Vette(s): 1976 L48 T-top, Automatic, ps,pb,a/c, Everything stock. Good car in great shape.
To all that helped me out I thank you...
So from reading past posts, I am going to install the manual valves on the hoses as I think the vacuum control valve might be stuck in the closed position or something as I am not getting any flow to the heater core.
One last question to everyone about this...do I need to drain the coolant level down to close off these valves in the summer? Also, when they are shut off, how can I make sure the heater core is not going to rust while it is not being used? In other words, do I drain it somehow when I close off the manual valves? Or does the water just stay in there all summer?
Thanks again!!!
in Forum: C3 Cooling and Heating Systems
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