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Old 11-19-2008, 05:30 PM   #11 (permalink)
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Quote:
Originally Posted by dichotomous View Post
yes, fast idle does not happen
Purely anecdotal... What were you experiment controls? Methodology? Fuel measuring devices?

Anecdotal evidence is worth next to nothing as far as evidence is concerned

That said, idle speed is not a great metric...
Case and point #1 - fully warmed up, the act of turning on my air conditioner results in no net change in rpm... But, an additional .1 gallons per hour is consumed and my throttle position changes from a 3 to 4 (where 75 is the maximum).

--------
On another note on the subject of toasty motors... Has anyone ever successfully implemented the Prius hot coolant thermos concept into another vehicle? If they spent the time and money to R&D it and then implement it - it's obviously something Toyota felt will bring gains to the part

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Old 11-19-2008, 05:45 PM   #12 (permalink)
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mmm...I could have used a nice warm blanky this morning...it was 17 degrees F where I was this morning at 6am... BRRR
Same here. I had a nice warm blanky until my wife ran me out of bed this morning. I think my digital thermometer read either 17.3 or 17.5 for a low this morning. That's cold even for Jan. & Feb. in the Charlotte, NC area, much less Nov. I'm ready for some normal temperatures, lows in the 30's and 40's and highs in the 50's & 60's. It's not uncommon for us to see 70's during the winter months. I use to work construction and can remember many times working outdoors in short sleeves during Dec. This has been an unusually cold fall for us. I think out high today has been in the low 40's.
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Old 11-19-2008, 10:20 PM   #13 (permalink)
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That blanket is primarily to keep heat from escaping during the rising expansion of air volume.

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)

A second use would be to help deaden noise and dampen vibration of the thin sheet metal of the hood, which causes further noise. Again, not the prime use, but one of the many uses.

So, those things said, and any other uses considered, the original poster's question was "will it be helpful to retain heat by putting a blanket on my hood". And the answer is still "no, it is more trouble than is necessary, and you'll face alot of stupid looks on your way back to the car."

Ford Man - I find it amusing that both of your fuel logs show close to the same mileage per gallon, yet based on your percentages above EPA rating, obviously the older car had a higher efficiency rating...

Is there a reason that auto-makers are allowed to continue saying that efficiency has improved since the 80's, when it so obviously hasn't?

C'mon.. since when is 30-40 MPG a landmark of efficiency? I've never gotten less than that in any small vehicle I've owned, including my trucks.
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Old 11-19-2008, 10:29 PM   #14 (permalink)
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I wouldn't go with the external blanket idea. Too much hassle even in good weather. drimportracing over at CMPG did a nice thread on insulating the hood on his Geo Metro.

Geo Metro Insulated Hood "how to" - CleanMPG Forums

Since you already have a fairly smooth underhood area, try the Al foil or Mylar idea. Al foil is cheap, but a mylar solar blanket is only a couple bucks and would provide one piece large enough for the entire hood as well as being slightly more durable. Mylar loses out to Aluminum by a couple percentage points in efficiency, but it's still over 90%. Since it's a radiant barrier and works by reflecting radiant energy, it's critical to keep it clean to maintain effectiveness.

I've been considering the mylar solar blanket approach as well. This idea could extend to any area where you're trying to reflect heat (undertray, AC lines, etc).
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Old 11-19-2008, 10:33 PM   #15 (permalink)
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Since you're questing to keep more heat under the hood, it may be a good idea to either:

Place the battery in a plastic box to reflect heat,

or

Consider relocating it to an area that is outside the oven that will become your underhood area.

Heat is detrimental to batteries just as much as cold is... there is a mean temperature at which they operate most efficiently.
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Old 11-19-2008, 11:11 PM   #16 (permalink)
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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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Old 11-19-2008, 11:23 PM   #17 (permalink)
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The underhood insulation is there for a sound deterrent. Any heat retention is incidental. If it was important to keep it warm under the hood, they would seal it up just like the passenger compartment. Rubber seam sealed and all.

A much better way to retain heat would be to pop the hood and put said blanket on top of the motor, avoiding any hot exhaust parts of course (don't want to burn the car down).

To answer the OP question - waste of time to try to add additional hood insulation.
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Old 11-19-2008, 11:56 PM   #18 (permalink)
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What about adding something like DynaMat to the areas of exposed sheet metal between the open areas of the structural webbing?

While DynaMat is normally used as a sound deadening device, it also has large basis in use as a heat-reflective material... lining the bottom of the car with it will help to keep cabin temps down.

That said, it's obviously covered with foil, which is heat-reflective, and might help to keep the heat from being absorbed by the hood and released into the atmosphere.

Cobra - When you say that heat retention is not necessary, you fail to logically understand the concern of the OP.

His concern was the if you warm the engine, it's more efficient than a cold one. Thus, keeping the underhood area warm will obviously keep the engine warmer, and it will run more efficiently from the first minute of the next start. He's not talking about retaining heat for hours, or days, but minutes. maybe an hour.

by the way, if you have read anything on this forum about efficiency, you would know already that heat retention is key in making an engine more efficient.. this "the OEM didn't do it, so it won't work" mentality is BS. It shows a considerable lack of evaluation skills. If that was the mentality of the rest of the world, we would not have most of the things that we have.

Please think twice before poisoning the board with this type of information.
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Old 11-19-2008, 11:58 PM   #19 (permalink)
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Quote:
Originally Posted by Christ View Post
Is there a reason that auto-makers are allowed to continue saying that efficiency has improved since the 80's, when it so obviously hasn't?.
MPG is a very poor efficiency metric. MPG/ton have been almost linearly increasing since the 70s. Even then it does not factor in performance.

Not too long ago I saw a pic of a very well made insulating cover for an Insight ICE. Can't find it again though.
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Old 11-20-2008, 12:10 AM   #20 (permalink)
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Not too long ago I saw a pic of a very well made insulating cover for an Insight ICE. Can't find it again though.
This speaks to another point: OEM's actually DO insulate the heat in the engine compartment.. that engine cover isn't just there for looks. They put them there in an attempt to keep the engine hotter for a longer period of time, and allow for less dissipatory heat loss. Reason? Heated engines both last longer, and run smoother, not to mention they have better net efficiency, and less emissions.

People tend to do the multiple short trip thing, and keeping heat under the hood longer will help with overall efficiency during those short trips.

The fact that MPG/Ton has been increasing says nothing, nor do I believe it.

Consider that my 1989 Civic DX weighs in just over 2000 lbs... and gets 30-40 mpg average. Now consider that cars are typically heavier than that... and get less miles per gallon.

I believe this says that net efficiency and MPG/Ton have BOTH been reduced. Next excuse?

To further debunk this, it doesn't matter if weight has gone down, since we all know that an engine that is pulling less weight is working more efficiently... so if vehicle weight has gone down, so has efficiency... case in point - a 4300 lb cadillac gets 25 MPG in 1981, yet a 3100 lb cadillac from 1991 only gets 21?

1000 lbs less, and still 4mpg LOST? I think something's up here.

Claim is busted.. how about instead of purveying a lie to the public, they waste their time thinking of a way to fix it?

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