I've replaced the heater core and cleaned the heater box on my '68 Cutlass with A/C and I am ready to re-install on the car.

What is the correct sealant to use to attach the heater box on the engine bay side to the firewall to ensure no leaks?

Rope caulk? Black silicone?

Thanks
Dave

 

Anyone ??

 

If you are thinking about the stuff that goes in that channel where the surfaces meet, the original material is a mastic-y caulking type material that that has a string in the center. I used the 3M strip caulking on mine.

 

I used 3M strip caulk, 3M#08578, about $20 a box. More than enough to do it.

 

I used Eastwoods stip caulk on my 54. I hope I never have to take it back out but it will be a lot easier than that tar like stuff they used in 1954.