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Discussion Starter · #1 ·
So I'm driving my '66 130 a fair bit and the rebuilt B18 is performing really well. It's end of summer here in Charlotte NC and it's been a hot one. I don't have A/C and may not ever; windows down, front and back vents open moves a lot of air. Still I seem to be getting a fair amount of heat coming through the firewall.

Is this normal/expected? I have done some insulation above the carpeting but could probably do a bit more. I reached up under there tonight and all the metal is pretty warm. Even the metal dash was warm.

It seems as though this heat pockets up under the dash and is felt as radiant heat on legs. There doesn't seem to be any airflow mechanism to move it out as I sealed up the firewall really well (grommets and then polyurethane caulk to seal the grommets). Maybe too well.

I know there is a firewall insulation kit (original was jute I think). Does anyone have experience with that?

I've been thinking of some sort of radiant barrier on the engine side of the firewall; one directly behind the head (tight fit) and down to the bellhousing and then something to block the radiant heat from the exhaust manifold.

Anybody else experience this and have any thoughts/solutions.
 

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Check the padding around the tunnel, and especially the hole for the shifter. There should be a layer of padding, then the air duct tightly stuck down to it, then the shifter boot, and finally the rubber mat. If the sandwich has any gaps, a lot of hot air will make it in.

Do you have a laser thermometer? Poke around under the hood, and up under the dash, and see if you find any hot spots. Take them one at a time, the car isn't really known for heating up like this. Maybe it's just a single issue.
 

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Its been a while (well into the previous century) since my first year physics class covering heat transfer and my second year engineering thermodynamics course; but, here goes! If you are thinking about a radiant barrier, keep in mind that in order to be effective, the radiant barrier needs a thermal break behind it (typically an air gap). A lot of the viscoelastic dampers sold for noise control have a foil covering and some people have touted this as radiant insulation. Not so! The viscoelastic pads are pretty solid and pretty effective at transferring heat!. What you want is a foil faced material with a moderately thick foam backing (thicker the better). To be effective, the foam backing should be closed cell. Slightly larger cells probably provide a higher R value per inch of thickness. At the risk of stating the obvious, the radiant barrier must be on the outside of the passenger cabin and the foil surface should not be touching anything. Anyplace where the radiant barrier is in contact with a hot surface, the reflective properties go done the toilet and heat transfer is limited by the thermal conductivity of the backing material.

A big item to consider with a radiant barrier is that its emissivity (ability to reflect heat) will be affected by surface contamination. If your foil surface gets dirty, its effectiveness as a radiant barrier once again goes down the toilet. You want to make sure that your B18 is a clean running engine.

On my 142, on the interior of the fire wall and extending down onto the floor pan and the transmission tunnel I applied mass loaded vinyl (MLV) with an attached foam backing that was about 1/4 " thick. I do not use any radiant barriers, although I am thinking about one for the bottom of my hood (noise and heat control). With the carpet and its attached underpad on top of the MLV I have no noticeable heat transfer through the lower fire wall and transmission tunnel. The heating problems I do have are due to a new, persistently sticky heater control valve and the solar heating associated with an all black leather interior and lots of glass. I think the solution to the latter problem involves wrapping the outside of the windows with aluminum foil :) .
 

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Wow Phil... those prices aren't bad at all. Sure beats the useless hay bail that comes apart in my eyes every time I need to look at anything under the dash.

Do you use these?

Mike
 

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I put one in an Amazon I was restoring for a customer in Arizona, and it was an excellent fit. Where I live, it rarely gets to 80F, so I can't really speak to its effectiveness first hand, but a lot of people I communicate with have used it and say it's great.
 

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Discussion Starter · #8 ·
Some great input and advice. I appreciate that. Looks like all the responders are from "up north" and some way north. Anybody with an Amazon down South experience this firewall heat transfer described in lead post?
 

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I've got a poorly sealed firewall, and the heat is (was? it's in pieces right now) brutal during the summer months, even up here in MN. My fiber mat is pretty disintegrated at this point, and my shift boot doesn't fit. Most of the heat comes from the tranny tunnel, but the bad grommet holes don't help.

I'm hopeful that better sealing (in progress), a new shift boot (in the mail from VP) and a new mat (see above) will solve my problems.
Mike
 

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Discussion Starter · #10 ·
Anyone have any normal operating temperatures on the head, side of block, etc from an infrared temperature gun? I'm curious what those results might be.
 
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