Grotesquified

Hello all!

I recently encountered an issue with my '78 Corvette. When I was driving it, I noticed that there was steam exiting the air vents of the car while I was driving. The main thing that perplexed me about this issue is that neither the A/C or heater was running (because I'm currently replacing the climate control panel, I have no way to activate these features) and unfortunately I haven't been able to rewire the dashboard currently to make my temp, fuel, battery or other gauges functional for now. I was just curious if any C3 veterans knew of any possibilities!

Thanks!

929nitro

Check coolant level and passengers side floor to see if it is damp. One possibility is a leak in the heater core.

Easy Mike

Do you smell antifreeze? The "steam" is likely to be coming from a leaking heater core.

Grotesquified

Thanks for the quick responses, guys! The floorboard doesn't seem to be collecting any moisture from what I can tell from driving it around for about half an hour. I was thinking it would likely be the heater core as well, but I'm a rookie DIY'er and wanted to know for certain before I open up the wallet to fix the issue.

Cooter Tech

You should be smelling anti freeze too, distinctive smell. If you are not sure if it is heater core, temporarily bypass heater core, see if problem persists. No leaks under car? Heater hoses are 5/8 and 3/4 inch in diameter. There are videos on changing out core, be careful with dash as it is fragile, and there are a lot of parts to remove to get to core. Hardest part is getting that large center air duct out. Take lots of pictures to help putting everything else back together.

Mr D.

My money is on a bad heater core

Alan 71

Hi G,
Your 78 has a vacuum operated valve, (small white striped hose), that shuts off the flow of hot water to the heater core when the a/c is operating.
If you could activate that valve and the steaming stopped you'd know it's the heater core.
Look at the upper left corner of this nice diagram. Notice the valve is in the engine compartment but the switch that controls it is in the interior.
Maybe?
Regards,
Alan

hunt4cleanair

hunt4cleanair

Yep! Heater core. Sounds like you caught it early enough that it has not leaked onto your floorboard. I replaced the heater core in my 78 a number of years and had the same symptoms...fog from the vents that eventually produced a film on the inside of the windshield.

Not a bad job as I remember. Pull out the passenger side seat so you have space to work. As Cooter states, take pictures to remind you how to reassemble the ductwork. The 78 design with glove box makes this relatively straight forward. But you'll also have to loosen the center console and remove the console side panels...those carpeted sections. Then pull the carpet back in the event when you remove the heater box, coolant that may have collected in the box, won't spill on the carpet.

By all means, pressure test the service replacement core before installing...as suggested, YouTube videos will show how to do this. The quality of new stuff is marginal compared to the original. Seems like these are now made in Mexico whether under the Delco name or otherwise. In fact, I would use the vendors that support the forum.

Rescue Rogers

turn on your defrosters and drive until you get the steam or fog. when it hits the windshield swipe a finger through it to see if its oily. its antifreeze if it is. if it isnt then its the AC creating a climate.Which would be a cloud

Cooter Tech

Because of all the different size and type of fasteners, I reinstalled them in the proper holes whenever possible or taped them together with a note as to where they go. Helps to prevent a lot of bad words. I pulled the center console and replaced all the bulbs with LEDS. Not to hijack thread, but it was while I am there issue.

Tampa Jerry

I would bypass the heater core and see if the steam goes away. If it does, you have your answer without the mess that will surely follow on your carpet. Jerry

gguillot

If you are in the humid south, steam from the A/C vents on humid days is not uncommon. I don't know about Oklahoma, but I'm sure you guys are getting your fair share of 96% humidity and 90+ degrees temp these days....