Excessive Cabin Heat

[Ghilliesuit]

First let me say hello, and it’s great to be a member of your community. I'm a proud new owner of a 1982 C3; she is the car I have been dreaming of since I was in High school. She has a professional restore with upgrades. The previous owner had a 400ci engine bored out 6 over with a holly 4 barrel, hooker comp header and side exhaust installed. Along with many upgrades and stock replacements. Pretty much under the hood she looks brand new like the day she was build with a big beautiful engine and 31k original miles on the frame.

Here is my question; I have noticed a lot of excessive heat coming from through the fire wall into the cabin. It feels like I have the heater running on my feet. That's great and all in winter but I’m stationed in Fort Rucker and it is hot hot hot. My first impression would be due to the larger engine and the side exhaust that I would generate a lot more heat in those areas, but this feels like forced air when the vehicle is in motion.

Is there some form of corrective action that I can take to lower / prevent this heat from entering the cabin? I remember reading a post on here while I was waiting for the purchase to finalize about a open vent in the engine compartment that was causing some issues for one member, but I have yet to locate that post again even with the search function. (Mod on a forum, hate it when people fail to use Search lol)

Any ideas would be greatly appreciated; my technical skill level on a 1-5 is about 3, meaning I can handle general maintance, installations, electrical, and troubleshooting with instructions. But iffy when it comes to primary engine / transmission disassembly and performance tuning. I’d rather let a certified mechanic make those adjustments to prevent extensive damage.


Thanks for any help you may be able to provide.

 

[fm1]

Look under the hood on the passenger side. Find the water lines, feed and return, that run from the heater core. There may be a manual valve on the feed line which will enable you to cut the flow of hot coolant to the heater core during the summer months. If there is one , close the valve. Temps will drop.

 

[Vettehead Mikey]

Your car was originally equipped with AC. This means there should be a vacuum actuated coolant shutoff valve on one of the lines going to the heater ass'y. Might be malfunctioning or has been removed. Cars of this age frequently have leaky air doors inside the assembly also. Simply shutting off the coolant will take care of most of the problem.

 

[Ghilliesuit]

Thanks, i'm going to jump under the hood right now. The previous owner had the AC system replace to run off modern refrigerant. Pretty much a new compressor, and the works. I'll report back if I this takes care of the Issue.

She still to hot for me to root around in, I like my arm hair and prefer the Burt Reynolds look. But i'm in the right area:

 

[Ghilliesuit]

Upon further inspection there is not a manual switch to turn off the heater core; I plan on taking her to the Auto Craft shop here on the installation and putting her on a lift so I can get a better look at the underside.

I did notice that the coolant reservoir was empty, this sparked me to dig a little bit deeper. I topped off the reservoir and noticed that there is corrosion on the outside of the radiator on near the filler cap. I see no obvious signs of a major leak and chalk it up to spillage.

This morning I finished up my interior detailing (getting her ready for when the wife comes back from vacation, she doesn’t know I bought her), and decided to check the radiator fill cap to see if the seal was good which might explain the spillage other than human error. The radiator was empty; I could not see any coolant. I also noticed that there is heavy corrosion inside the radiator. I was under the impression the previous owner changed out the radiator when the engine was upgraded.

Would a simple flush remove all this build up or do I need to go ahead and swap out the radiator? I was told the engine temp gauge was not tuned to the new engine and it would stay pegged out once the engine reached operational temps.

I’m in the process of ordering an AIM, has any one purchased this one Corvette Corvette Assembly Manuals, 1956-1982 - Corvette Parts and Accessories it seems rather inexpensive, but most of the others I have found on the net or that are posted here are $75 plus. I want to make sure I’m getting the right thing.

 

[6880 Mike]

...I’m in the process of ordering an AIM, has any one purchased this one Corvette Corvette Assembly Manuals, 1956-1982 - Corvette Parts and Accessories it seems rather inexpensive, but most of the others I have found on the net or that are posted here are $75 plus. I want to make sure I’m getting the right thing.

You need only the 82 assembly instruction manual (AIM). A compilation of everything from 56 through 82 might make nice reading, but it's over kill. You are likely to find the 82 GM chassis service manual to also be helpful. If you don't have one, order an 82 owner's manual. Lot's of useful information in the owner's manual.

 

[Vettehead Mikey]

Would a simple flush remove all this build up or do I need to go ahead and swap out the radiator? I was told the engine temp gauge was not tuned to the new engine and it would stay pegged out once the engine reached operational temps.

The low coolant level will cause the pegged temp gauge, hopefully you haven't damaged the engine by overheating it. There is no need to tune the temp gauge to a new engine, assuming that this is the stock sensor.

Find the source of the leak and fix it. Flushing a rad will make it a leak worse. Replace it if it's bad.

Be aware that the AIM will only show how to assemble the car, no fix it or tune up info.

 

[Ghilliesuit]

Trackin all, thanks. I'll clean up the spot were the dried coolant is and give it a run to temp and see if there are any signs of leakage. It would be obvious because of the pressure in the radiator would make it seep.

Understand all about the AIM, if I'm able to see something in exploded view i can fix it. Father taught me young, he was a motorcycle mechanic.

 

[Peer81]

Your coolant heater shot off valve should be on top or near the top of the heater box in the engine compartment. It's a vacuum valve and a black vacuum hose with a small white stripe should be connected to it. Try removing the vacuumhose and connect it to a vacuum meter, with the temp switch all the way to cold it should read around 13 to 15 Hg (depending on your cam I think) With lower Hg vacuum the valve will not shut compleetly and hot coolant will continue it's way into the heatercore.

If you have no vacuum, open the glovebox and remove the interior plastic, you should see the top of the heater box and on top is a handle that should press a switch when it is set to full cold. On my 81 the handle didn't tough the switch so no vacuum was send to the valve vacuum hose. Of course an easier way is to put in a manual valve.

But first check your coolant problem, is more important then the interior temperature.

Greetings Peter

 

[Ghilliesuit]

Thanks peter i know just what you are talking about, i changed the picture above to reflect. This afternoon i will follow your advice. I plan on driving around for a bit, stopping to check the radiator, then ending at the auto craft shop. I want to put her up in the air and check out the under body. I'm going to have to upgrade the front and rear supension (little squeak drives me nuts), but that can wait till I return from Korea.

 

[Elliott]

I had the exact same problem with my '79. We were going to need to get behind the dash to resolve the problem with either a valve, damper or both. So instead we installed a manual shut-off valve in the heater hose going to the heater core. Problem solved completely! Elliott

 

[Ghilliesuit]

@ Elliott Do you happen to have the part number for the manual shut off you installed or is it a common part from the local auto parts store?

 

[Peer81]

I see you found the valve looking at the above picture!
I fixed everyting with the original parts and now I feel a big difference between the temp switch being at full cold or 1/8" right from full cold.

And if it would still be to hot with everything working properly. The floorpan on top of the transmission doesn't have any isolation. Makes a big difference isolating it.

Btw. Fully fill the radiator and the coolant tank between cold and hot. With the engine hot always check the coolant tank and never open the radiator to check the coolant level. Under pressure hot coolant goes up when opening the radiatorcap!...

Greetings Peter

 

[Ghilliesuit]

Engine running at normal temps now, no signs of leaks yet. Most likely just Pi$$ poor maintance. I checked the vacuum line, and it's not pulling any Hg's, i'll check inside the glove box tomorrow loosing day light and the nats are about to eat me alive.

On a side note i got her up in the air and boy do i have a big shopping list now. Front and rear supension need to be replaced (bushings bad). Trany oil leak needs a new seal and might as well clean out the filter inside. Lots of dangling wires, and the power antenna isn't hooked up.

Thanks for all the help guys, i should be able to close this issue out before the end of the weekend.

 

[Elliott]

We bought our '79 last summer and it was a cool evening when I bought the car; didn't notice the heat problem. Later in the summer it felt like I had the heater on high and we nearly baked! I actually heard of this solution from someone on this site. I believe my mechanic actually got the shut-off valve from a plumbing shop. Nothing special or unique about it. It's a small lever valve; turn it 90 degrees to open or close. We live in Iowa so during the summer I close it and when it gets cool in the fall I open it up. If you want a photo of what I put in, send me a private message with your email and I will send one. Not sure how to load photos on this site. Elliott

 

[Ghilliesuit]

lol its funny you say that, the tech at our auto craft shop told me just go to the hardware store and get a metal ball valve and that would do it.