Dash Heater Core Leak

If I was going to use a stop leak, it would be the one which consists of the aluminum flakes. I have used it a few times in the past and it worked every time, without clogging all of the core passages or leaking again after a period of time unlike Barrs leak (black stuff) which clogged up everything, but also stopped the leak. I would check the unit as others have mentioned, and see if it is somewhat accessible. If it is, I would probably just replace the core unit. A lot of the newer vehicles today have them under the dash where you must rip the whole dash out to access it, hours of work to get to and 10 minutes to change it. Some rv's are much easier to access due to placement than cars or pickups.

The problem is sometimes the entire dash needs to be removed, very pricey, labor-wise.
My thought is try the stop leak. If it works, you've saved hundrejds of dollars.
If it doesn't...pay up.

If radiator stop leak can stop up a hole in a heater core or radiator, I wonder what it does to those small passages that the antifreeze travels through? Personally, I wouldn't use it.

Using stop leaks in a radiator is okay, but certainly not a permanent fix. You are only postponing the inevitable, which is replacing the heater core.

Use the stop leak for now, but save your pennies for the replacement down the road.

And no, they are not a scam. They do work.

I had a leak in my old pick up. I suggest fixing it sooner than later, we let it go for about one yr, when I finally discovered I was poisoning myself and my husband was a pinch away from being on 'Forensic Files' for killing me!

Let me guess, you have a Ford F53 V10 with an Acme Air HVAC system. If so, the cause of the leak is expansion from the high flow pressure from the V10. Later versions of the ACME design were better able to with stand the flow dynamics. The heat exchanger is enclosed in a clam shell and changed out from the front of the firewall.

I had a leak in a 1994 Ford Van 12 years ago I put in Barr's stop leak. The heater core was near impossible to remove. It hasn't leaked since. Also used it in my brothers truck 4 years ago and it is not leaking.

If you don't travel when the heater is needed just bypass the core by connecting the two hoses together with a coupling.
If you do need the heater, the Stop Leak additive MAY work long enough for you to make permanent repairs. Perhaps YOU can remove the core and take it to a radiator shop to repair. This is pretty standard work for a shop and shouldn't cost too much, even if you have to get a new core. The high cost is the labor hours to remove and re-installing the heater core.

find the two hoses going into the heaterunder the hood, get a hose coupling and a couple clamps and bypass the heater.

fix it the right way.
rad leak stop is a quick fix (junk)
it could hold a day a year who know how long