So--after a 2.5 yr frame of resto of my 65 cutlass convertible all is well until i notice a drip under the dash from the heater box-- I know what that means--heater core leaking. I changed it about 10 yrs ago and it still looked fresh so it was NOT replaced during the resto. The question is what type of sealant will not react with the metal on the core? It looks to me like the caulk I used 10 rys ago reacted with the metal and caused the leak. The core looked perfect except around the edge where it was seated in the sealant. This is inside the heater box on the back of the core--not around the box against the firewall under the hood. The chassis manual says to use caulk or body sealant.

 

What particular sealer did you use on it?? Seems like it was corrosive or something.
The factory used a tarry-like rope sealer, kinda like 3M Strip Calk. This is what I used last year and hope this is the right stuff!

 

I don't know of any sealant that would cause corrosion.

Methinks you're barking up the wrong tree.

- Eric

 

I used Phenoseal and it corroded the core at the edge--i believe I am awake and it is definitely leaking. I googled sealants that will not corrode metals and it looks like I need an Alkoxy based silicone--any other silicone sealant can cause corrosion to metals. The 3m tape sounds good, however I am going to do my homework this time--antifreeze is on my new carpet!! Original core-lasted 35 yrs--replacement 10.

 

If you say so, but in over forty years of working on various sorts of cars, I never saw any modern sealant corrode metal.

I'd still consider other sources, or just the fact that modern replacement heater cores are junk.

- Eric

 

The Phenosealph is stated to be between 7 and 12. If close to 12, that is pretty strong. Strip Calk is pretty neutral.
And yes, the new cores will not last as long as the originals. An original is 3lbs, a new one is 2, which means thinner metal.

 

A couple of pics--

 

Of course it can be just spent. I am assuming it was related to the sealant as the car is not driven much so not that many cycles of pressure. It looks to be perfect except where the sealant is. I do not remember the brand core I purchased, but I usually will buy a quality part if given a choice such as Rockauto does. I purchased a Spectra Premuim to replace this one. There is info out there related to caulk and sealants reacting with different metals but sometimes I probably read too much. It does look really good- as seen in the pics-and I believe it was leaking in the rusty corner of the box. I found a cut out rubber like gasket in my Cutlass drawer that was in the old heater seal kit--I am going to use it this time and ignore the manual. This will keep the core off the box.

 

FWIW, last time I replaced my heater box - I used roofing sealer in a tube.

Lasted a few years+

 

The Spectra core is made in china. It is not the original shape and although it fits in the box, it does not fasten in correctly with the clips--ordered one from Napa that looks more like the removed unit. It says Spectra also but looks like the copper tanks--the ng one is aluminum.

 

That is why I had an original Harrison heater core redone.

The aftermarket stuff is pure chineseum junk.

 

I ended up having my non original but still copper tank re-cored with a new copper core. It is amazing how heavy it is--over 5 lbs. It looks like he used a lot of solder so that accounts for a little. I am hoping this is the last time i visit this problem. Work was done at Perraults Radiator in Meriden CT--nice people. A couple picks.