Heater core vacuum test

[Kansan]

My car has a heater core bypass when I bought it and the guy I bought it from said it hadn't been hooked up since he bought it in 2008. That worried me a bit, thinking there may be a bad heater core, Well this little feat of garage engineering has held a steady 15" of vacuum for the last 20 minutes. Would you say it is safe to say it likely won't leak when I run the system with coolant or is there a possibility of a leak once the core heats up?

Kansan

 

[mrmopar340]

My car has a heater core bypass when I bought it and the guy I bought it from said it hadn't been hooked up since he bought it in 2008. That worried me a bit, thinking there may be a bad heater core, Well this little feat of garage engineering has held a steady 15" of vacuum for the last 20 minutes. Would you say it is safe to say it likely won't leak when I run the system with coolant or is there a possibility of a leak once the core heats up?

Kansan

View attachment 143585

If you dont have A/C it's an easy swap if it fails.

 

[Kansan]

Actually, I do have A/C which is why I'm hoping this core is good. I'm pretty confident at this point it is good.

Kansan

If you dont have A/C it's an easy swap if it fails.

What would be the pass/fail criteria?

Thanks

Kansan

 

[terrywalker]

Hmm, when mine failed recently, I thought of it as an easy swap since there's no A/C. Well, here I am a month later after I pulled the heater box out to change the core. I removed the bucket seat, shifter and cassette player so nothing would be in the way. I had a rebuild gasket set from DMT seeing as the foam gaskets were all shot. I decided to clean up all the heater doors inside before applying new foam material to the doors. I then thought I may as well replace the carpet since I had a new one on the shelf. I pulled out the other seat, the back seat, the interior panels, and noticed the floor pans looked terrible. So, I cleaned up the floor pans and repainted. The carpet was placed out in the sun on a 100 degree day. It's now placed in the car waiting for trimming once the folds relax, etc. etc. This just kept snow balling on me. The new core was okay but I massaged it for a better fit. Cleaned up all fasteners. The heater box looks great. I just need to finish carpet install, trim it and put heater box back in and install the entire interior. So much for my easy swap...
By the way, I did a easy core swap in my Charger with A/C. It snow balled into a new interior just like the Challenger. BTW, if there's any doubt in your mind if the heater core is good, change it out. If it suddenly gets a leak while driving at normal temperature/pressure, that's going to be a tough mess to clean up.
Terry W.

 

[moparleo]

Now try the same thing with 16 lbs of pressure.

 

[Kansan]

Now try the same thing with 16 lbs of pressure.

Will do. I know my pump will eventually start leaking down about a pound after an hour, How long should a measure for a steady value? 30 minutes?

Kansan

 

[terrywalker]

Something to consider. If the heater core was bypassed because of a leak, the sediments in the core can be acting as a temporary seal with your vacuum test. It could be the person changed the core and decided they weren't going to use the heater anymore, but... If in doubt, I'd change it out. Just be aware the heater box may need a rebuild to replace all the foam seals. Just my opinion.
Terry W.

 

[mrmopar340]

Hmm, when mine failed recently, I thought of it as an easy swap since there's no A/C. Well, here I am a month later after I pulled the heater box out to change the core. I removed the bucket seat, shifter and cassette player so nothing would be in the way. I had a rebuild gasket set from DMT seeing as the foam gaskets were all shot. I decided to clean up all the heater doors inside before applying new foam material to the doors. I then thought I may as well replace the carpet since I had a new one on the shelf. I pulled out the other seat, the back seat, the interior panels, and noticed the floor pans looked terrible. So, I cleaned up the floor pans and repainted. The carpet was placed out in the sun on a 100 degree day. It's now placed in the car waiting for trimming once the folds relax, etc. etc. This just kept snow balling on me. The new core was okay but I massaged it for a better fit. Cleaned up all fasteners. The heater box looks great. I just need to finish carpet install, trim it and put heater box back in and install the entire interior. So much for my easy swap...
By the way, I did a easy core swap in my Charger with A/C. It snow balled into a new interior just like the Challenger. BTW, if there's any doubt in your mind if the heater core is good, change it out. If it suddenly gets a leak while driving at normal temperature/pressure, that's going to be a tough mess to clean up.
Terry W.

That swap made a lot of work for you. They aren't hard to change but then you say "I'm going to fix this while I have it out" and then you see all the other things....

 

[terrywalker]

Exactly. We have all been there... I'll just fix this. Then I may as well fix this while I'm at this point. Snowballing...
T walker

 

[Steve340]

If it held the vacuum you should be OK - or it is blocked.
Run it with just water in the cooling system and a few old bath towels in the footwell for a few days.

But they are old and do fail - so maybe just replace the core with a new/tested one as a previous poster suggested.
This should eliminate a failure anytime in the near future.

 

[Kansan]

Run it with just water in the cooling system and a few old bath towels in the footwell for a few days.

Excellent idea! Thanks for the tip. There are a few things I'm doing over the winter, but just getting it together for the fall.

Kansan

 

[MOPARMITCH]

My non-air conditioning heater box was out of the car since I'm doing a full restoration on my '70 Cuda. Before I went to Carlisle I took the heater core out of it to ask Bob at Glen Ray radiators to test it. Took it to him and he said, oh we don't test them.. I'm like WTF. He says we just recore them. Mine is an original numbers matching date coded. Not that anyone will see it. Anyhow. He says $200 to recore it. Ummm no I will take it home and test it myself. Blocked off the big hose with a cap and used a hose with the tire valve on the other one. Filled my slop sink up with water and put it under water with 35 PSI on it. I saw no bubbles. I'm calling it good.