Insulation under the car (to reduce heat gain from pavement)

[Piwoslaw]

Would insulating the underside of the chassis help reduce heat gain from the hot pavement? And heat loss in coldest of winter?

Or is this negligible?

[Ecky]

My guess is that most heat gain/loss will be through the windows, so probably not significant. There's already a layer of sound insulation and carpet over the floor pan.

[elhigh]

Adding a belly pan is already a good idea; if you have a belly pan down there then carefully applying a layer of foil for a radiant heat reflector could provide the kind of results you're looking for.

Just be careful you don't accidentally insulate the heat of your exhaust system inside the belly pan space.

There are clear or nearly clear window films that are supposed to be really good at reflecting heat back out of the window - clear enough that you can legally apply them to the windshield, which you certainly can't do with tinted films. You can't get them on the consumer market, they have to be applied by certified installers.

[Baltothewolf]

Originally Posted by Ecky

My guess is that most heat gain/loss will be through the windows, so probably not significant. There's already a layer of sound insulation and carpet over the floor pan.

As a Miata owner, I disagree.

OK but really though, if it's not a modern car then some lightweight heat reflecting tape can do wonders. On a miata it can lower transmission tunnel temps by 30-50F and the floorboard right above the exhaust by a significant amount. When I'm cruising on the freeway in my Miata I can feel the radiant heat coming through the carpet.

[Daschicken]

What, you can't put up with the heat? I use my A/C more in the winter than in the summer, thanks to windshield defrosting. Okay, I don't know how hot it gets where you live, and I drive a white car with white interior, so my car doesn't get too hot.

Originally Posted by Baltothewolf

As a Miata owner, I disagree.

OK but really though, if it's not a modern car then some lightweight heat reflecting tape can do wonders. On a miata it can lower transmission tunnel temps by 30-50F and the floorboard right above the exhaust by a significant amount. When I'm cruising on the freeway in my Miata I can feel the radiant heat coming through the carpet.

The miata lets in a ridiculous amount of heat through the transmission tunnel. Great in the winter, terrible all other times. I have never driven any other RWD car that radiates as much heat from that tunnel than the miata. Balto, you going to FWA 2018? I have been converted.

[cRiPpLe_rOoStEr]

This thread reminds me the day an Opel Corsa that my dad used to have when I was a teen had an ignition coil failure, and the catalyst overheated. I could feel the excessive heat irradiating through the floor.

Anyway, I'm totally favorable to adding some insulation to the floorpan of your car. I usually see some folks using those aluminium-faced reflective foils under the floorpan, even though some actually do it in order to patch rusty spots (or the holes drilled to bolt CNG tank subframes when they're not desired anymore)

[oil pan 4]

Put the insulation on the inside.

[Baltothewolf]

Originally Posted by Daschicken

The miata lets in a ridiculous amount of heat through the transmission tunnel. Great in the winter, terrible all other times. I have never driven any other RWD car that radiates as much heat from that tunnel than the miata. Balto, you going to FWA 2018? I have been converted.

Nah I'm only doing FC and BLFC this year (already did FC, was a blast).

You got telegram?

[ASV]

thermal mas is better off inside the insulation wether your dealing with exes heat or insufficient heat. So put the insulation on the outside
R-Tech foam boards seem to hold up to weather well if not exposed to UV
and can be gotten with a reflective aluminum skin

[mattrod]

I heard good things about dynaliner. A cheap alternative is Frost King duct insulation.