Heater box sealant

[Dave K.]

I used a thin black srtip caulk as a sealant around the heater box to firewall on my 66 roadster and was docked a point for being non typical. The sealant is to be more runny and liquid as opposed to the strip caulk. I've investigated the previous threads and see the strip caulk referenced and the black gooey sealant but no mention as to what could be used to replicate the gooey sealant. I was thinking of rubber based undercoat but wanter other opinions. I've removed all of the strip caulk around the heater box.

Thanks,
Dave K.

[Gary Schisler]

Re: Heater box sealant

Dave, a number of years ago, someone suggested using the stuff they use when the "mop" the tar-like substance on roofs. You have probably seen these things - large heated vats where asphalt based products are heated up and then mopped onto the matt to seal the roof.

Gary

[Dave K.]

Re: Heater box sealant

Gary,

Stuff was sprayed on not brushed.

Dave K.

[John D.]

Re: Heater box sealant

Dave, You should have left the strip caulk on. I heard tell that guys are using a heat gun after they put the strip caulk on and it looks like real deal. Hair dryer won't work. Get a heat gun or borrow mine. Then massage it some and it will fly. Saw it done one time. Better than roof cement. Wouldn't know though!! Ask BH about it. John

[Dave K.]

Re: Heater box sealant

John,

Thanks,

I have a heat gun -- but I'll call to discuss.

Dave K.

[Gary Schisler]

Re: Heater box sealant

Dave, I understand that this was sprayed on. However, I have read where others heated this stuff up and then dribbled it on. It sounds like John's method may be easier.

Gary

[Terry F.]

Re: Heater box sealant

It was poured on on my 68....or maybe it was just starting to warm up and could barely run out the spray gun??? Terry

[John H.]

Re: Heater box sealant

The gooey, runny black stuff was a water-test repair sealant that was used in repair and intermittently on the main line; it wasn't part of the normal heater blower case installation.

[Chuck S.]

Re: Heater box sealant

That stuff used to seal the firewall grommets and the heater box looks like (as Gary says) a hot molten tar, but I doubt GM would have messed with that. It appears to have been "dribbled" on the top of firewall grommets and heater box joint rather than sprayed...it does have runs.

John Hinckley has the best description of the product. I doubt you can find anything close to that today unless it's the black, asphalt-based waterproofing sold in the Southwest for evaporative coolers. Once that product cures hard, it looks pretty close. The front plenum on C3s is completely painted with the stuff...you find a good substitute or you don't mess with it.

[John D.]

Re: Heater box sealant

Dave, Dave Cardina did a nice job of putting a sealant on my '63 heater core cover. Has his own invention He did not use a heat gun on my car. That's another friends invention. But I saw the results at Marlborough and it looked good. My 63 looks ok also. Judges did not ding me on it at Marlborough. Maybe they were too beat from having to judge a ton of cars though. Felt sorry for them. Glad I was sitting on easy chair for a change. Although wasn't easy as two big wigs kept picking on car a lot. Well knows guys too. Can't mention their names as want Duntov for little white car. Course have to PV first. Never owned a Vet that could PV though. Brand news ones. Nothing ever worked. Dealer fixed long list of complaints and utter crap broke on way home. Way of life back then. But we loved it. Today the boys want the cars to run like new. DOn't think so as when they were brand new they didn't run. Have proof of that. Ask Clem. John

[Joe L.]

Re: Heater box sealant

Dave-----

For C2 era cars, the AIM says that the sealer used for the blower box to firewall interface was neoprene solvent adhesive. This is the same type of cement used for gaskets, weatherstripping, etc. It's what we know today as 3M Weatherstrip Cement aka GM #12345097. I don't know if the original cement was the "yellow" or the "black" variety. However, I strongly suspect that it was the yellow which ages to dark brown.

For C3 era cars, things changed. For those, the AIM specifies "black pumpable sealer". This product was never available from GM and I don't know of an aftermarket source for it. However, I would think that something like black RTV silicone sealer would provide a similar appearance, if not the same "feel to the touch".