Greetings,

Been lurking for awhile but this is my first post.

A bit of back story: Bought a 95 Corvette from out of state and on the way to get it smogged here in Aurora, CO, fourth gear blew out. My son had checked it out before I bought it, so it was running fine up until the time it wasn't. Bad luck, huh? Anyway, I pulled the trans and shipped it to ZFDoc down in Arizona. While under the car attempting to remove the flywheel I noticed some drips coming from the frame under the passenger side close to the fuel filter. It wasn't fuel, so decided to look closer at the coolant. The car has been up on blocks for months so it hasn't run. Long story short, it looks like coolant is dripping from the bottom of the AC evaporator housing, as the hoses running to the heater core and the serge tank appear dry and in good shape. I felt the carpet and kick panel on the passenger side and could find no obvious moisture there, so I'm a bit perplexed. Thus this post.

So, is it possible that a leak from the heater core could make its way to the bottom of the AC evaporator housing? Naturally I'm dreading replacing the heater core if I don't have to, but that seems to be the likely culprit. I've searched the threads but was never able to get an answer to this particular question.

(In the photo there is evidence of dripping down the side of the serge tank. While a leaking cap is a known issue my car hasn't run under pressure in a while and the coolant level in the tank is now well below where a leaking cap could account for it.)

Many thanks to all who reply!


Bottom of AC evaporator housing where drips of coolant appear.


Heater hoses behind serge tank. No obvious signs of moisture.

 

I’m certainly no expert. But I have recently replaced both the A/C evaporator and the heater core in my 95. The heater core is completely inside the car. Unless the car is nose down 30 degrees I don’t think it would be the heater core leaking into the evaporator housing.

 

Hey, thanks for that. I'm no expert either; that's why I'm here. LOL

Well, if it's not the heater core I'd really like to find out where it's coming from because short of tearing into the dash, I can't really see how coolant could be finding its way inside the AC evaporator case. Been busy with work so I haven't been able to delve into it further, but will soon. My car is currently up on blocks with the wheels removed as I'm having the six speed transmission worked on, but it is level and there was no coolant leak for a long time; then one day it just started dripping. This is a case for Sherlock Holmes.

 

Might have been someone careless filling the surge tank. Spilled on the blower housing and leaked down. The blower housing is split in half near the mount of the surge tank on my 95. There isn’t a seal between them. The factory used a soft tar like substance called butyl or some I think call it dum dum.

If there was a gap or excess amount of antifreeze, I could see it entering the housing and later coming out of the condensation drain.

 

That is an interesting theory, and could account for what I'm seeing except that the coolant level in the serge tank has actually gone down, so I do have a leak from somewhere. (The tank itself shows no signs of leaking.) I haven't drained the system yet hoping that that would help me better determine the source. So this isn't just some excess spillage working it's way to ground, as much as I wish this were the case.

I did watch a YouTuber taking off the AC evaporator housing and the bottom where the cases meet is definitely the low point of the entire affair, so if coolant were somehow making its way from the heater core side, it would definitely show up dripping from exactly where I'm seeing it. I just don't know if such a path for a coolant leak is possible, but it would explain everything.

 

You can remove the fan resistors from the blower housing. They are located on the top of the blower housing next to the mount for the surge tank. You will be able to see inside the blower assembly housing to see if there is any antifreeze.

Looking at photos from mine. The heater core pipes go through the firewall directly. They do not enter the blower assembly. The heater core in the car is actually slightly lower than the opening in the firewall.


You could try pressurizing the radiator with a hand pump. I’m sure you know this already.

There are tools to pressurize the coolant system to find pressure leaks.

Changing the heater core is not bad at all. I would definitely pull the top dash. Makes it much easier and there is not that much work involved.

Good luck

 

I'd hadn't thought to look into the housing by removing the blower motor resistors. I'll look into that. Thanks for the tip.

Winter and work are keeping me from doing too much sleuthing but when and if I find something concrete I'll post it for the next poor soul who reads this hoping to find some answers.

Glad to hear changing the heater core is "not bad at all," which must rank as an all-time minority opinion. I'll have to see what I think when the time comes.

 

So I removed the fan resisters and it looks to me like the coolant is coming from the heater core. You can see moisture at the bottom along the firewall, and it appears at the bottom of the evaporator casing. I know PatrickBowersJr stated that there is no way a heater core leak could make its way to the bottom of the casing but I can't account for any other source of the leak than the core.

My next step will be to remove the passenger kick panel and see if there is any sign of leaking from that direction. I'll keep everyone posted as to what I find.

 

That looks like quite a leak. It does look like the heater core.

The passenger footwell would be wet too with that much fluid.

 

Back side of the passenger kick panel showing that leaking coolant is possible to present itself both inside and outside the firewall. Who knew?


Behind the kick panel and metal cover, this is what I need to remove to get to the heater core housing, which is that black shiny thing behind the black box in about the middle of the photo. So far it's been nothing but loosening bolts and screws, and the electrical connectors to the seat. Nothing too mind bending.

 

And that is why mine's simply bypassed.

Until I feel like screwing around with it anyway. It's been four years. So far I just ain't feeling it. Not looking like a go any time soon either...

 

I hear you. I can't exactly say I'm looking forward to this, but another part of me tends to be fascinated by what's under the skin of an automobile, and while I'm taking things apart I can't help but imagine the assembly workers putting all this stuff together thirty years ago.

Maybe changing the clutch and pilot bearing on an old 944 I used to own makes jobs like this not seem so daunting. After all, everything's right there.

 

In my opinion, the heater core on my 95 Corvette was not difficult at all. Go slow. Keep track of the bolts and nuts. It can be done in a weekend. Really no special tools needed. I think I did the whole job with a 1/4 in socket set, pliers, screw driver and a torx driver set.
While you are at it, you can flush the coolant and replace it. I could not believe the amount of sealant GM used in the pressurized tank with radiator cap. I used a hose to wash it all out.

 

Great advice. So far, I have to agree with you regarding how easy this job is (knock on wood). Yes, lots of steps, but nothing in and of itself seems all that difficult. And yes, I do intend on replacing the coolant, hoses, thermostat, and even those knock sensors in the lower block since the coolant has to be drained anyway.

Any advice on a preferred mfg of heater core? I see Rock Auto has one that's popular by Four Seasons that goes for $31.79. Whatever one I put in, it needs to be reliable, for obvious reasons.

I'll be posting more photos of my progress for those who follow after.

 

I will probably be in the minority here, but I prefer the aluminum core 4 Seasons. Mine had the factory copper. I was concerned about dissimilar materials increasing the chance of electrolysis.

I replaced all my hoses, thermostat and water pump. I blew out the system with my shop vac and then refilled with Zerex G05. On refill it was close to 4 gallons 50/50 mix.

 

With dash panel removed, more tidbits are revealed; the airbag on my '95 taking the place of the non-explosive glove box.



Close up of the airbag. Removing the four silver nuts (only two visible in picture) allows it to lift out. It was a lot heavier than I thought it would be. At the upper left is one of the silver brackets that hold the two screws securing the central defroster cover. You can disconnect the sensor by twisting it 90 degrees until the tangs line up so it slides out of the plastic grill piece. Once a seemingly endless amount of 7mm screws are removed, the dash panel cover comes up and out with a modest yank or two. If you're doing this job solo, have something ready (like a cardboard box) for the side you're not on to support the cover when you remove it (my seat had already been removed on the passenger side, so there was nothing there for support). The cover is a bit bulky and it's 30 year plastic old; you don't want it flopping around any more than necessary.

 

Remove the airbag by removing the 4 bolts and then disconnect the electrical cable directly behind the unit.