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Firewall pics/advice wanted

Craig Artzner

Craig Artzner

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Hey. I put a new heater core and hoses in my K5 back in '06 and need to know how to seal the firewall openings where the two hoses go through to the core (I've had duct tape there since I did the repair). I don't remember what was there before (some kind of caulk maybe?). I looked everywhere for grommets of some kind but came up empty. The holes aren't completely round, sort of elongated. Anyone know what I should use?
 
I just used 100% black or whatever color silicone you want in a caulk gun from the hardware store. 100% silicone won't eb effected by the heat and will last almost forever. And you can peal it off someday if you need to remove it.

I wouldn't use caulk, get's dried out and hard to remove over time.
 
Don't use silicone. Silicone will cause rust rapidly. It's a huge no no in the auto glass industry. Go get a tube of urathane from your local auto glass place. You can also use any sealant that is butyl based. Both of these when dry, stay plyable. Both of these will adhere nicely to anything that is clean of dirt. If you tool it after applying it, you can make it look really nice.

I have always used this to seal any wires or tubes, that I have ran from inside out or outside in. Stays nice and weather tight.
 
rockink5 said:
Don't use silicone. Silicone will cause rust rapidly.
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What? :confused:

I guess you'll have to tell my other car that has had silicone around the entire heater box opening and fittings for 14 years that it was supposed to be all rusty along time ago, because I don't still see a spec of rust around the silicone. Silicone is pretty inert, paint won't even stick to it or too a surface that it's been on without fish eye remover, I guess if you used it wrong before painting it could cause a problem but that's not silicones fault.
 
folkenheath said:
What? :confused:

I guess you'll have to tell my other car that has had silicone around the entire heater box opening and fittings for 14 years that it was supposed to be all rusty along time ago, because I don't still see a spec of rust around the silicone. Silicone is pretty inert, paint won't even stick to it or too a surface that it's been on without fish eye remover, I guess if you used it wrong before painting it could cause a problem but that's not silicones fault.
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Well, then you must have done something right. But being that I have had to be recertified every year for the last 15 years in auto sealants, I still hold to no silicone. Yes it is the silicones fault. The acetate in the silicone will eat away automotive paint. If there is ANY moisture under the silicone when applied, it will be trapped and cause rust quickly. Urathane dries with help from humidity. It will absorb a bit of moisture while drying.

Don't use silicone on a vehicle. Leave the silicone for use around your bath tub.
 
I use a form of "rope dope". I get it at a local A/C automotive place. Thats what they use. I comes in rope form so you can mold it to any shape you like plus it stay pliable. I look n see if I can find the name of it.
 
Craig,

My 1986 (with A/C) may be different, but IIRC the inlet and outlet tubes (which are pretty close together) had an oval foam gasket that was installed over those tubes before the heater core was installed from inside the Blazer.

So when everything was done, that foam gasket was pressed tightly against the firewall (from the inside) by the heater core.

My memory is failing me, but I think I got a new one from my local Chevy dealer.
 
British Slave said:
Go to a heating/ airconditioning shop and gets some "duct seal" comes in one pound blocks.
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Yeah thats the stuff. Come to find out when the shop is slow the guys take the block and roll it into rope so its ready when they need it. Then they just coil it onto cardboard and suran wrap it. I always thought it was weird that there was never any labels on the packaging lol.
 
another vote for windshield urethane, of course once you use it you will realize with it and Duct tape you can not only fix your truck but they are both so handy you will wonder how you lived so long with out
 
don't get windshield urethane on your hootus... :haha:

you could just run 3M 5200, same stuff...

black "dum dum" for windshields is a "not as permanent" solution.... comes in waxpaper backed rolls...
 
rockink5 said:
The acetate in the silicone will eat away automotive paint. If there is ANY moisture under the silicone when applied, it will be trapped and cause rust quickly.
Click to expand...

OK, so this makes sense to me and I'll look into that urethane for future use. What you siad before kind of shocked me with no reasoning but this is more logical. I wonder if the type of paint matters then, maybe that's why I've had good luck in that application.
 
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