Engine insulation for hybrids to improve fuel economy

[hayden55]

Make a bag out of reflective insulation and tape it up with aluminum tape and toss your ceramic fiber in. Also underhood temps on my black ls400 only ever got to 160 degrees when i measured this summer. Don't go touching your headers or heat shield though.
I agree i hope my fiberglass insulation doesn't get wet. Its doing great for now as it doesn't get wet.

[Phase]

so the wool or ceramic fibers?

[Isaac Zachary]

Mineral wool. Super wool. I'm not too sure about ceramic fibers.

[hayden55]

https://www.homedepot.com/p/UniTherm...50in/309949108

The factory just uses yellow fiberglass insulation on the fire wall with a good cover over it. The ceramic stuff is fire proof and has a higher insulation value. You can throw it in a fire to test it before you use it if you are nervous.

[Isaac Zachary]

But is there a difference between Mineral Wool and Ceramic Fiber?

[freebeard]

Mineral wool
Mineral wool is any fibrous material formed by spinning or drawing molten mineral or rock materials such as slag and ceramics. Applications of mineral wool include thermal insulation, filtration, soundproofing, and hydroponic growth medium.
More at Wikipedia

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[Phase]

Ideally it seems like I should avoid fiberglass since I need something thinner and more stable with better insulation. My hood to engine area is pretty tight on the Ioniq. I haven’t measure the distance but it’s pretty small

[Isaac Zachary]

Originally Posted by Phase

Ideally it seems like I should avoid fiberglass since I need something thinner and more stable with better insulation. My hood to engine area is pretty tight on the Ioniq. I haven’t measure the distance but it’s pretty small

That's why I recommend Mineral Wool (or Rock Wool, etc.) It stays fluffed up on it's own, unlike fiberglass insulation.

[Talos Woten]

Originally Posted by Phase

Asked my car buddy who works on cars this. Excuse his language. But it got me a bit worried and concerned.

I’m just looking for the safest, most stable and least messy way to insulate the top

If we just flat out ignore prices, what’s the best solution possible? What would an OEM automaker put who specializes in winter vehicles in Alaska do?

What material is not flammable? Apparently fiberglass, mineral wool, and ceramic are all bad now?

I agree with your buddy that just laying down insulation on top of the engine is questionable. Aside from moving parts there are also bumps and vibration that might abrade the envelope. Attaching to the hood with a gap seems safer in my mind.

The current insulation reigning champion are aerogels:
https://www.aerogel.com/about-aerogel/
but that is hideously overpriced and better suited to other applications (like space flight where every ounce costs money to launch).

There are at least four factors that we want to consider for an insulation in the engine compartment.
1) Temperature. Since most compartments won't be above 200F, virtually all insulations mentioned will be fine temp-wise. The only potential issue is failure cases like an engine overheating, in which case you'd want something rated past 300F just to be safe.
2) Flammability. Engine fires happen, and we have to account for them. This rules out any kind of paper, cellulose, etc. and makes us favor mineral wools, which are already known for their non-flammability. Ceramic fiber is a kind of mineral wool.
3) Longevity. Many kinds of insulation are hydrophilic, which long-term degrades their insulation capacity and/or structure. This is a notorious weakness of fiberglass bats. However, in this application, moisture will likely be regularly baked out of the material, so it's less of a factor.
4) Cohesion. We want the material to retain its shape and to not flake into the engine compartment. This rules out all fills, grains, etc. It also makes us favor pre-made insulation that is faced or sided.

So after the whole analysis, mineral wools come out on top because of flammability. If you dropped that constraint, then a whole range of insulations (including foam et al) would then be viable. Oh, mineral wool is also generally hydrophobic with good cohesion, which is why I chose it in my own case.

If you are just looking to buy something, the product Isaac Zachary linked is great. Any faced mineral wool would work... the only thing I would do is try to find something in a larger single piece, and cheaper. That makes it easier to install, and easier on your wallet.

Good luck!

[cRiPpLe_rOoStEr]

Originally Posted by Talos Woten

Many kinds of insulation are hydrophilic, which long-term degrades their insulation capacity and/or structure. This is a notorious weakness of fiberglass bats. However, in this application, moisture will likely be regularly baked out of the material, so it's less of a factor.

I remember seeing fiberglass taken out of old fridges looking as if it was rotten, most likely due to moisture and mold growing on it.