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

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???

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.

Balloon material == MYLAR.

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

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

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

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 :thumbup: Throw a temperature probe in there and log the temperature every 15 minutes or so.... Add the blanket, then do the same :thumbup: 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 :/

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.

Can you provide some empirical evidence for your claim?

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 :thumbup:

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.

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.

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).

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.

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.

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 :thumbup: 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 :p

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 :p) - but improvements are to be had.

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

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.

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.

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.

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?

You should do a bit more reading. It is accepted as a very good indicator of powertrain efficiency. It have been increasing steadily 1.2% each year for the last 22 years.

How exactly does it say that powertrains are more efficient? I just got done debunking it by showing that MPG has not gone up while weight has gone down... it's quite easy to make a comparison rise while not actually having any good effect.

I can say that I have 5 apples and 5 oranges, and I want more oranges...

I now have 50% apples and 50% oranges.

Now, I remove one apple.. Now I have 4 apples and 5 oranges... I can say it this way now: I've taken away 20% of my apples, which shows irrefutably (sp) (read: without a way to challenge) that I have more than 50% oranges, and less than 50% apples... thus, I must have more oranges now... b/c I have more than 50%.

To quantify:
Remember, 5 minutes ago, I had 50% oranges, and 50% apples.
I didn't add any oranges (MPG), but I DID remove apples (weight).
My ratio went from 1:1 (even), to 5:4... skew that result over 22 years, and you have something that looks alot better than it is.

Think what youre saying... if it's gone up steadily by 1.2% each year, that means that over 22 years, MPG/Ton would have gone up more than 22% (rule of compounding percentages suggests closer to 40%)

That said, I don't remember ANY car in history losing 40% of it's original weight, nor getting the like in additional efficiency... in fact, if this WERE the case, we'd hardly be in the predicament we're in.

For the sake of your own sanity, please don't read so far into a single subject, and begin thinking further than the first search result. No offense intended.

You may read into my answers as far as you want, fact is, MPG has stayed the same, or even varied slightly, while weight has gone down, which still says that overall efficiency has also gone down, for the reasons I've stated previously.

How many "experts" here have tried underhood insulation?

I've only done it to the extent of relieving underhood noise and vibration... never to keep heat in.. I was always against that, actually. Being a racer, I determined that it's a bad idea to rev an engine to 9k constantly and keep all that heat in.. something will melt.

I've done it and it does indeed help.

Help with what? FE or noise/vibration? If it helps with FE, I'm a douche, and I'll be engineering something to put back on my hood... roffle.

It does make things noticeably more quiet.

It does retain engine compartment heat noticeably better, allowing for quicker warm-ups. Getting into closed loop is much quicker thus FE and emissions are better.

Do I have temp probe test results? No. Do I have FE charts before/after? No. Still, I know it works.

Works even better with a grille block.

Material choice doesn't even need to be hi-tech. I think a large component of it working is simply in reducing compartment drafts (convection losses). On my car there is no room for anything more than a single thickness of corrugated cardboard to span the entire engine compartment. On my pickup I have the luxury of using foil faced 1" thick foam board.

P.S. I started fooling with this stuff about 14 years ago cuz I hadta commute through crap conditions kinda like this:

http://i146.photobucket.com/albums/r.../Blizzard1.jpg

I wanted to be kinder to my engine, and I wanted more instantaneous defroster function at the end of the workday.

Not exactly scientific, but at least a positive basis for which to start testing.. good input.

BTW, you say your tempo needs a 5 speed swap? Get one from an escort. The pedals and all fit, the shift linkage has to be made to fit.

My dad used to have an 89 Topaz... we took the pedals from his 86 Escort and the 1.9 engine's tranny... put everything in the Topaz, and it worked perfect. The 1.9 will actually bolt into your car, if you can get it... I'm not sure about the mounts tho... as in which ones to use.

Sorry for the OT.

Jah- Tempo/Escort front ends shared just about everything. I kinda hate to do it as the a/t has low miles and functions perfectly- if it ain't broke don't fix it right?... but on the other hand, it's old-school inefficient. 28-31 just doesn't cut it in a car that size.

That's the thing, if you're not happy with it, it's broke. Get fixin'!

In fact, if you're anywhere close to Bradford County, Pa, my dad has that same transmission that we used before... he'd probably let it go for $50. He doesn't have the pedals, but he has a 1.9 carb'd engine that has sat in the barn for god knows how long... he hates to get rid of stuff.

I'm pretty sure if you're close enough to him, you could get some great stuff to play with at some really good prices.

Message me or something if you want more info, so we don't jack this thread.

I'm too far away.

I think it's worth testing ;)

But - I'm not concerned of convection off a warm hood.... It the heated air in the engine bay - if it's not heating the hood, it's going to try and go elsewhere unless something stops it from physically moving out of seams, cracks etc.

Obviously... it's still going to expand and cool and it would be very difficult to physically contain all that heat... but thermal diffusion from the hood (IMO, anyway) is one of the major places that the heat goes when it's not properly insulated.

As was stated previously, adding a grille block and largely limiting dynamic flow through the engine bay may be a pre-requisite for a reflective blanky to actually do something, but most of us have that already anyway. Maybe it's that extra 1 or 2 mpg that keeps us able to drive when gas prices go back up?

Won't know until it's tested. I mentioned roofing felt and aluminum foil or mylar the other day simply because they're both alot cheaper than dynamat... stuff is wayyy too expensive for what it does. (poorly, at best)

Christ, MPG/ton is miles per gallon per ton.

A 30 mpg vehicle weighting a ton have the same ratio as a 15 mpg vehicle weighting 2 tons. It's useful to measure how efficiently you are moving stuff around. It allow for comparison between cars, light trucks, big rigs, freight trains, planes, etc. For passenger cars this ratio has been steadily increasing.

I've got an SAE paper on it I read not to long ago. I'll dig it out.

So here's where I'm confused... you say that a 30mpg vehicle that weights one 1 ton... (that would be 30/1=30 which makes it 30:1)

will have the same MPG/Ton ratio as a 15MPG vehicle weighing 2 ton... (once again - 15/2 = 7.5 so it's 7.5:1)

How do they have the same MPG/ton ratio? To make them the same (mythbusters addict) we'll do a little experiment.. let's swap some numbers.

30mpg vehicle weighs 2ton, therefore: 30/2 = 15 so 15:1
15mpg vehicle weighs 1ton, therefore: 15/1 = 15 so 15:1

NOW they have the same ratio. This still proves exactly what I said earlier... even if that 30mpg, two ton vehicle weighed only 1 ton (for a reduction of 1 ton of weight over 22 years) The change would appear considerable, in that the ratio would change from 15:1 to 30:1 (30mpg / 1ton = 30, so 30:1)

THE ENGINE is still not any more efficient. It's still only able to net 30mpg, even though there is less work to be done.

HOW, I ask, does that make those numbers anything more than garbled BS that the industry came up with to prove they're making a difference, when in reality they're pocketing the extra money from NOT making a difference?

You need to control work (F*s) - otherwise, we're not comparing the same thing ;) We want to compare FE to the amount of work done. Because that's what cars do - turn chemical energy into {hopefully} useful work :)

I'm going to cheat with my units a little by using something other than conventional :p
To move 1 ton * 1 mile = 1 ton*mile
To move 2 tons * 1 mile = 2 ton*mile

To do the same amount of work, the 1 ton vehicle needs to move 2 miles....

1 ton * 2 miles = 2 ton*miles

So,
2 miles/ 30mpg = .0667 gallons
1 mile/15mpg = .0667 gallons

This is why loaded semi trucks, trains, ships, etc. are VERY efficient methods of moving "stuff"


Consumption wise, sure - the train eats more than the 30mpg car.... But the car can't move that sort of tonnage :thumbup: Per pound, the train consumes much much less :) It's not the engine that's more efficient - it's the system.


:thumbup:

Ok, I understand that. Or at least it makes more sense now, although I still think it's mostly a fallacy.

My point was that car makers are spouting off that engine efficiency has gone up considerably over the last 20 years.

Looking at the statements I've made in the last few posts, that is obviously not true.

To some degree, it has.... Which is how less aerodynamic cars than mine produce more power with better FE number (grrrr).... There's room for improvement - for a CR ratio of 10, the theoretical max is circa 60% for an otto cycle... Realistically, we're falling around 25/30% or so. Otto Cycle -- from Eric Weisstein's World of Physics

MetroMPG has a picture posted somewhere showing weight dependent mpg versus year.

It's important not to confuse mpg with thermal efficiency ;)

Getting back on topic, check this out

http://www.99mpg.com/Projectcars/ran...imgp2017.jpg,0
Engine Blanket Installed


http://www.99mpg.com/Projectcars/randallsinsight/

Thanks for the link!

This is the one I saw before. http://www.99mpg.com/Projectcars/ran...0/top_side.jpg