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my dad just landed a 71 convertible. While driving yesterday I noticed heat coming from around the tunnel/dash area. Is there a temp control? Is there a thread somewhere for this?
Very common issue with C3s. When I first had my A/C upgraded, it could not keep up with the heater-core still functioning and cockpit temps began to rise. Some research on this forum claimed that the heater core HAS to be shut off in the summer. The original shut-off valve runs off vacuum and, well, doesn't work well.
NAPA sells a manual (heater hose) shut-off valve that can be hidden down by the original valve. NAPA has the valve in 5/8" & 3/4" so it can be spliced into either heater hose going to the core. The valve is threaded-seat type and is fully adjustable if you want to run a little defrost or heat. This upgrade will make a HUGE difference in cockpit temps.
The heat you may be feeling is more than likely the radiant heat from the transmission tunnel area where it gets hot and can radiant that heat into the cabin.
Installing a heat barrier that is much better than the just GM used will aid this. I have had great results by using the DynaMat Extreme and the DynaPad to stop this heat issue. Others have used other products with what they say have given them good results also.
Assuming that all of the grommets in your firewall where wiring harnesses and vacuum hoses go through it are plugged up and sealed off.
And also assuming that you were NOT having heat coming out of your ducts in your dash also.
A torn lower shifter boot can allow a lot of heat from under the car to get into your shifter console area also.
There is a foam seal that seals off the back of the engine/bellhousing area to the firewall that helps divert the heated air from the engine compartment also. More than likely it is not there. It helps.
Also the is an aluminum covered piece of insulation that the factory installed on the underside of your transmission tunnel that aid in stropping heat but it is NOT the only thing you need to do if you still have this radiant heat.
Thanks guys. The car does not have AC. So how do you shut off the heat? I don’t see a temp control anywhere.
Everything DUB said above applies if you're having heat issues not related to your actual heater system.
As for the heater itself:
The heater controls are just above the shifter.
Push both thumb wheels all the way up to turn off the heat. Pull both vent ***** (to the left & right of the heater controls) to open the kick panels at your feet.
That's all you get until you put the top down.
As you have no A/C:...
The left wheel controls where the air blows (defrost, vents, feet) the right wheel simply controls how much air is allowed to pass over the heater core.
Non- A/C cars do not have a heater shut off valve for the water going to the heater core.
If you think the heat is coming from the heater you can always disconnect the heater hose going to the core. Most simply loop the two ends together (5/8" to 3/4" connector required).
I wouldn't say most people loop the heater hose ends. The day after you do that bubba set-up, you will need to defrost your windshield. Could be very dangerous not having any control of the defog / defrost if its raining.
The NAPA heater hose shutoff valves are around $22. After installed and you get into some bad weather just pop the hood and open the valve, simple.
I wouldn't say most people loop the heater hose ends. The day after you do that bubba set-up, you will need to defrost your windshield. Could be very dangerous not having any control of the defog / defrost if its raining.
The NAPA heater hose shutoff valves are around $22. After installed and you get into some bad weather just pop the hood and open the valve, simple.
Didn't say most people loop the heater hose ends.
I said "you can always disconnect the heater hose going to the core. Most (who do this) simply loop the two ends together"
Last edited by Hammerhead Fred; Oct 6, 2018 at 11:58 PM.
You can install a simple valve on the 3/4" hose that goes into the heater core, and shut it off for summer. Works excellent and made a huge difference in reducing my interior heat. Anytime it gets cool or rainy and you need heat or defrost, just turn it open and presto.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
I like that kind of shut off valve but I would like to attach it directly to the manifold or water pump, what size adaptor would I need and where can I buy one?
I like that kind of shut off valve but I would like to attach it directly to the manifold or water pump, what size adaptor would I need and where can I buy one?
I bought this one at a local home center, and it had the hose barbs on it already. You can buy threaded versions, I'm sure, and will need to find the appropriate fittings on your own to plumb it to the pump or intake. I put it in the hose as it hides away nicely along the side of the engine compartment.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Thanks for the reply. I have the same shut-off valve installed in the same place, I also have one on the 5/8" hose and just thought that it would look better and be more convenient to get a nipple that would screw into the intake and water pump and be barbed on the hose end so I wanted to know what size the threaded end is.
I've been told I only need one valve but since I have two I'd like to continue to use both.
In theory if both hoses are shut off pressure could build in the heater core and cause it to rupture due to over pressure or vacuum. Water does expand and contract with temperature change.
Yes, that makes sense. No wait. It doesn't make sense. Yes it does! No it doesn't!
If BOTH valves were closed, there would not be any pressure on the core. But wait. If either valve leaked ever so slightly then yes, there would be pressure.
Same goes for negative pressure (vacuum) which would happen during engine cool-down. If both valves are closed then . . . . .
I always figured two shutoff valves were an overkill. But it sure could keep some carpet from getting wet.
The pressure is a result of the water expanding / contracting.
If it's 60 degrees when you close the 2 valves and the car sits in the sun at the beach it's now 150+ degrees in the car. The heater water will expand and pressurize the water - maybe to the point of damaging the core.
The opposite can also happen - close the valve when you remember, engine running and hot - hot water 160 - 180 degrees. Let the car sit and it's now 45 degrees out - there is a vacuum (- pressure) in the core - which it was never designed for.
Does it fail ? it's a real possibility.
Plus you have stale fluid in the core for how ever long the valves are closed. With one valve there is some exchange of fluid due to the change in pressure, (controlled by the rad cap) even though there is no flow through.
Last edited by BLUE1972; Oct 9, 2018 at 09:18 AM.
Reason: h
I placed mine on the hose near the tire well, if you put it on the manifold you will need to check your hood clearance and also trim down the handle. on the hose it is neatly tucked away out of sight and a little more astetic.
I agree. I don't want those ugly-*** valves where anybody can see it. Some look like they belong on a washing machine.
I hid mine near the original valve / firewall.
Why not use a "factory vacuum valve on the inner wheel well like the factory did. Run the vacuum hose to manifold vacuum and just unplug it in the winter ? (of course plug the open line) The manifold vacuum will close the valve, and it will open when you unplug it.
This is what I did on a friends 72 as they don't have factory hot water shut off.
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Hi, garretthes,
I'm sure that by now you understand that the quickest way to eliminate cabin heat is to install one shutoff valve on either heater hose, as illustrated by JoeMinnesota.
Also, follow the information that DUB offered as he is an expert and restores Corvette's for a living.
Blue 72,
Yes, I do have two shutoff valves but I am not sold on your theory about expansion and contraction having a negative effect on the core. Both valves have been installed since 7-29-2008 and the core has not leaked.
I can remove both the water pump and manifold nipples and get the correct diameter and thread size but it would be easier to have the new nipples on hand at the start of the job so that is why I asked if someone knew the size.
HeadsU.P.,
Beauty is in the eye of the beholder. Which is uglier, the original vacuum operated valve or the ball valves?
Heater Question for 71
