Hood blanket... literally? (engine compartment thermal insulation)

[Sean T.]

I know that most hoods have a "blanket" under them to insulate the engine compartment... I plan on getting a second one just to beef up the insulation.

I have been thinking... would it be worth it to get a large blanket or quilt and bungee it to the hood of the car when I run into the store or something, to keep the car warm if I am going to be more than 10 minutes? Or even to leave on my car while I am in class...

The theory seems to be good, but practicality might be difficult because if it snows, then I am stuck with a snow covered blanket to clean off and fold back into the trunk...

Anybody have any comments or thoughts???

[Christ]

Not worth it, honestly.

But, in lieu of cleaning off the blanky, just leave it strapped on there lol.

Cool thing about lots of snow buildup on your car - opportunity to see how your cars shape affects airflow, and what shapes you should attempt to achieve when going for aero mods. Don't do this on the highway... FTA says its' illegal now. So does NHTSA.

But honestly, you don't actually lose enough heat through your hood while sitting to worry about anything, it will become more hassle than it's worth. If you're really worried about it, try a one time thing: Aluminum foil and roofing felt.

Remove the "blanky" from under the hood of your car, apply roofing felt en gappe (in the gaps) between the webbing. Make sure to cut the pieces to fit perfectly, and put them in place with some temp-resistant adhesive. Then, take alum foil, or if you're feeling really expensive, get some of that stuff they make balloons from...

Use thin contact adhesive (heat resistant) and glue it to the hood's blanky before pinning it back up in place.

Principle: We all know heat rises. The roofing felt further insulates the hood, the foil is reflective, so it will reflect the heat back toward the engine.

[Christ]

Balloon material == MYLAR.

Heat suits are made from it, as well as solar blankys.

[Daox]

Underhood 'insulation' is more so there for sound deadening reasons than heat reasons.

[Funny]

mmm...I could have used a nice warm blanky this morning...it was 17 degrees F where I was this morning at 6am... BRRR

[Christ]

Originally Posted by Daox

Underhood 'insulation' is more so there for sound deadening reasons than heat reasons.

Why does it matter what it's there for, when we all know what it actually accomplishes?

Sure, they put it there so people wouldn't be offended by engine noise... but insulation of any kind will retain heat, and you don't think they designed part of the engine management system around that extra heat?

[trebuchet03]

Originally Posted by Christ

Why does it matter what it's there for, when we all know what it actually accomplishes?

Sure, they put it there so people wouldn't be offended by engine noise... but insulation of any kind will retain heat, and you don't think they designed part of the engine management system around that extra heat?

I'm not convinced that it will be beneficial enough to be measurable.... My house has a fair bit of insulation - but it will get cold quickly with the windows open. Unless the engine bay is fairly sealed, it's going to be drafty in there :/

I think you're fighting natural convection more so than conduction through the hood. Maybe the reflective barrier will be useful for radiation losses.....

It's worth testing methinks Throw a temperature probe in there and log the temperature every 15 minutes or so.... Add the blanket, then do the same If everything is right, you should get two logarithmic plots. I used to have a $15 meat probe thermometer used for such testing, alas, it broke :/

[dichotomous]

the 10-30mi you are in a store will not cool an engine enough to where it would need to heat back up to be efficient. engine blocks stay warm for hours. heck, my open to the world aluminum Vtwin in my bike doesnt use fast idle at lunch after sitting half a day at work! and like I said, thats an all aluminum deal with no hood or blanket, just literally sitting out in the wind naked.
I also have a carbon fiber hood on my car, with no heat blanket (and thus has cracked the top coat, but thats besides the point), and it used to have a ceramic coated header, and it would take hours to get "cold". now with bare stainless steel race pipes it would take longer.

[trebuchet03]

Originally Posted by dichotomous

the 10-30mi you are in a store will not cool an engine enough to where it would need to heat back up to be efficient.

Can you provide some empirical evidence for your claim?

[dichotomous]

yes, fast idle does not happen