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Old 11-19-2008, 11:11 PM   #16 (permalink)
trebuchet03
MechE
 
Join Date: Dec 2007
Location: Bay Area
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The Miata - '01 Mazda MX-5 Miata
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Quote:
Originally Posted by Christ View Post
That blanket is primarily to keep heat from escaping during the rising expansion of air volume.
An external one, yes... I don't see that happening for placement between the hood webbing/structure - it's not sealing any holes open to the environment.

Quote:
Originally Posted by Christ View Post
Underhood areas aren't necessarily "drafty", though they're obviously not sealed. The blanky holds more than one core purpose, based on those facts.

We could find it safe to say that while the blanky is somewhat effective in holding heat into the engine bay, it's more effective at reflecting the rising heat, and thus is used to protect the paint on the hood of the car from damage due to heat soak. (Talk to carbon fiber hood guy... he can tell you)
The connotation behind the word draft might lead you to believe that I'm saying there's a large air velocity. I'm not saying that - I'm saying that natural convection is likely the largest cause of heat loss. Warm air will move upwards, hence uninsulated CF hood finish damage. If it has a place to escape, it will - all the while drawing up cool air from under the car.

Anecdote: I can feel warm air escaping from the hood gaps on my car - and from the cowling, etc. This is why my front windshield doesn't dew up as fast as my rear one does - there's a slow trickle of warm air escaping from the engine bay It's also why my sister's outside temperature sensor gets way hot if the car is stationary with a hot engine - 115F in winter? I think not

Slowing conduction through the hood will prevent the hood from warming - but it's not going to stop a fluid from finding an exit. At least, this is what intuition tells me. At the same time, intuition says that a radiation reflector would be beneficial - metal hoods are already OK in terms of emissivity (unless you've got a dull black hood in there ) - but improvements are to be had.

What I'm getting at is.... Insulation between the webbing is worthy of testing If not the optimal solution, a cheap, low/no maintenance, and "invisible" one
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