Why put insulation under the hood?
10-14-2021, 03:08 AM
#1
Member
Thread Starter
Why put insulation under the hood?
I was surprised to see a black sheet of insulation under the engine hood. I thought these i6 engines were notorious for overheating in the cherokees?
My insulation is looking pretty ratty and was gonna remove it or replace it, any advice? I live in new york so it gets down to the 40s or so a lot during the winter. Thanks!
My insulation is looking pretty ratty and was gonna remove it or replace it, any advice? I live in new york so it gets down to the 40s or so a lot during the winter. Thanks!
10-14-2021, 06:19 AM
#2
Senior Member
The insulation is there to protect the paint on the hood; you absolutely need it to keep the paint from failing...
The cooling system on a XJ works perfectly fine in Phoenix level heat on a stock XJ. Once you lift it, install things in front of the grill, take it off-roading and want to run A/C, then it's marginal. Not saying there's a lot of margin built in, the radiator is quite small, but it works just fine for a vast majority of applications. Heat generated in the transmission towing up long grades is the only heat issue in most in most XJs, and even then, it's only an issue if you OCD about things that generally were fine before. Nothing like putting a temp gauge on a setup that has been running fine and is generally recommended for hotter climates. There's more bad info on the internet than there is good...
The cooling system on a XJ works perfectly fine in Phoenix level heat on a stock XJ. Once you lift it, install things in front of the grill, take it off-roading and want to run A/C, then it's marginal. Not saying there's a lot of margin built in, the radiator is quite small, but it works just fine for a vast majority of applications. Heat generated in the transmission towing up long grades is the only heat issue in most in most XJs, and even then, it's only an issue if you OCD about things that generally were fine before. Nothing like putting a temp gauge on a setup that has been running fine and is generally recommended for hotter climates. There's more bad info on the internet than there is good...
10-14-2021, 06:40 AM
#3
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Year: 2000
Model: Cherokee (XJ)
Pretty sure my '96 had one.
My '00 did not.
And pretty sure I have yet to see a '97 and up with one.
But it is listed in the parts catalogs for those years so....
Since you have one I think if it were me I would replace.
I toy with putting one in my '00.
The paint on my hood was messed up when I purchased it and I always wonder if part of the reason was cause there isn't one.
Like Jim said.
When I had the hood redone I had the louvers done at the same time.
One reason that I have not done this yet is cause I have to hack it up cause of the louvers.
Be a shame to hack up a brand new one.
Figure would be better in the winter but during the warmer months maybe not so much.
Maybe one of these days.
I will say one thing though. Does a nice job of cleaning up the engine bay. LOL.
My '00 did not.
And pretty sure I have yet to see a '97 and up with one.
But it is listed in the parts catalogs for those years so....
Since you have one I think if it were me I would replace.
I toy with putting one in my '00.
The paint on my hood was messed up when I purchased it and I always wonder if part of the reason was cause there isn't one.
Like Jim said.
When I had the hood redone I had the louvers done at the same time.
One reason that I have not done this yet is cause I have to hack it up cause of the louvers.
Be a shame to hack up a brand new one.
Figure would be better in the winter but during the warmer months maybe not so much.
Maybe one of these days.
I will say one thing though. Does a nice job of cleaning up the engine bay. LOL.
10-14-2021, 06:54 AM
#4
Senior Member
Quite a few self-adhesive, "Dynamat" type products out there that would work in place of the OEM insulation. I suspect they removed the insulation (97+?) when they went to the return-less fuel system (96?) and started seeing heat-soak issues... DIdn't get so bad that we would notice until they put the Cats in the downpipe later on.
10-14-2021, 07:23 AM
#5
Member
Thread Starter
yeah id love to see some less fiberglassy nasty looking mat thing and instead see some kind of carbon fiber based product...
Man if I could start all over, I might just wanna be a Cherokee expert and trick em way out for a profit... that doesnt sound so bad a life.
Man if I could start all over, I might just wanna be a Cherokee expert and trick em way out for a profit... that doesnt sound so bad a life.
10-14-2021, 10:15 AM
#6
CF Veteran
To answer this question, Originally I think it was a matter of trim level for noise purposes, as is on other models of cars. For instance I have two Crown Victorias, one with and one without and they are different trim levels. As to the hood heat, yes it helps there too and helps save the paint
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10-14-2021, 10:48 AM
#7
CF Veteran
it helps keep hood cooler, but probably does little in so far as harming engine cooling. The heat will still exit the engine bay just fine, the heat will exit out the front, rear, sides, even down, but less heat will be transmitted out into the hood and its paint. But it is not if that heat will be trapped and cant get out via other means to the front sides, and bottom. The insulation redirects the heat flow to other paths to exit, thus keeping your hood cooler.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
The heat shielding above the exhaust manifold doesnt really make your exhaust manifold all that much hotter, trapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simple find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
The heat shielding above the exhaust manifold doesnt really make your exhaust manifold all that much hotter, trapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simple find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
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10-14-2021, 10:57 AM
#8
CF Veteran
it helps keep hood cooler, but probably does little in so far as harming engine cooling. The heat will still exit the engine bay just fine, the heat will exit out the front, rear, sides, even down, but less heat will be transmitted out into the hood and its paint. But it is not if that heat will be trapped and cant get out via other means to the front sides, and bottom. The insulation redirects the heat flow to other paths to exit, thus keeping your hood cooler.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
Take the metallic heat shielding above the exhaust manifold for instance, it doesnt really make your exhaust manifold all that much hotter bytrapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simply find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
think of a house in the winter. If you heat the home heat will escape into the attic, so you insulate the ceiling below the attic, now the attic will be cooler, and your home warmer, however if you open the windows in the home, the insulation on the ceiling wont make much difference in home temp if the windows are left open, but the attic will still be cooler than with out.
the engine bay is like a home with open windows, the hood padding will keep the hood cooler, so now more heat will flow out via other paths, thru the the other openings around the engine bay. It wont cause your engine bay to get much if any hotter to be any concern.
Could be the padding was stopped being used simply as a cost reduction.
I like cool hoods.
i got the padding, and wheel in the desert, drive highspeed on hiway in desert with heavy loads, I run cool. some say I am cool, other say my coolness as a person is debatable.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
Take the metallic heat shielding above the exhaust manifold for instance, it doesnt really make your exhaust manifold all that much hotter bytrapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simply find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
think of a house in the winter. If you heat the home heat will escape into the attic, so you insulate the ceiling below the attic, now the attic will be cooler, and your home warmer, however if you open the windows in the home, the insulation on the ceiling wont make much difference in home temp if the windows are left open, but the attic will still be cooler than with out.
the engine bay is like a home with open windows, the hood padding will keep the hood cooler, so now more heat will flow out via other paths, thru the the other openings around the engine bay. It wont cause your engine bay to get much if any hotter to be any concern.
Could be the padding was stopped being used simply as a cost reduction.
I like cool hoods.
i got the padding, and wheel in the desert, drive highspeed on hiway in desert with heavy loads, I run cool. some say I am cool, other say my coolness as a person is debatable.
Last edited by robsjeep; 10-14-2021 at 10:59 AM.
10-14-2021, 07:18 PM
#10
Senior Member
it helps keep hood cooler, but probably does little in so far as harming engine cooling. The heat will still exit the engine bay just fine, the heat will exit out the front, rear, sides, even down, but less heat will be transmitted out into the hood and its paint. But it is not if that heat will be trapped and cant get out via other means to the front sides, and bottom. The insulation redirects the heat flow to other paths to exit, thus keeping your hood cooler.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
Take the metallic heat shielding above the exhaust manifold for instance, it doesnt really make your exhaust manifold all that much hotter bytrapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simply find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
think of a house in the winter. If you heat the home heat will escape into the attic, so you insulate the ceiling below the attic, now the attic will be cooler, and your home warmer, however if you open the windows in the home, the insulation on the ceiling wont make much difference in home temp if the windows are left open, but the attic will still be cooler than with out.
the engine bay is like a home with open windows, the hood padding will keep the hood cooler, so now more heat will flow out via other paths, thru the the other openings around the engine bay. It wont cause your engine bay to get much if any hotter to be any concern.
Could be the padding was stopped being used simply as a cost reduction.
I like cool hoods.
i got the padding, and wheel in the desert, drive highspeed on hiway in desert with heavy loads, I run cool. some say I am cool, other say my coolness as a person is debatable.
Without, you can get hot spots on the hood, specially when stopped with a hot engine. I notice a big difference in hood temps with and without the insulation. However the insulation does little if any difference for over all engine temp. Remember its job is to redirect the heat away from the hood, it is not some sort of heat trap that will cause bad under hood temps, rather it redirects the heat away from the hood so it will exit elsewhere.
Take the metallic heat shielding above the exhaust manifold for instance, it doesnt really make your exhaust manifold all that much hotter bytrapping heat, rather it serves to protect the intake and parts around it from getting too hot, the heat simply find a different less damaging path to get out with this type of shielding
there is also likely some sound deadening involved too, but I have not been able to detect that verses jeeps with and without it. but the hood is certainly cooler with it.
now when they added the two catalysts inside the engine bay, and as pointed out removed the fuel return, yeah heat is more still a problem. My buddy has a 2001 and his lacks the hood padding, but his is a lower trim level than mine, maybe high trim levels still had it with twin cats? His hood cooks however, specially right over the cat area.
I dont think the pad on the hood increases engine bay temps much if any at all, but it does keep the hood a bit cooler.
think of a house in the winter. If you heat the home heat will escape into the attic, so you insulate the ceiling below the attic, now the attic will be cooler, and your home warmer, however if you open the windows in the home, the insulation on the ceiling wont make much difference in home temp if the windows are left open, but the attic will still be cooler than with out.
the engine bay is like a home with open windows, the hood padding will keep the hood cooler, so now more heat will flow out via other paths, thru the the other openings around the engine bay. It wont cause your engine bay to get much if any hotter to be any concern.
Could be the padding was stopped being used simply as a cost reduction.
I like cool hoods.
i got the padding, and wheel in the desert, drive highspeed on hiway in desert with heavy loads, I run cool. some say I am cool, other say my coolness as a person is debatable.
10-15-2021, 01:18 AM
#11
CF Veteran
The 1st and 2nd Laws of Thermodynamics combined dictate that heat transfer is already occurring by those other means you reference at the maximum possible rate for the conditions. There's no spare capacity, it's all being used, 100%, all the time, rule of physics. When you reduce heat transfer in one part of the SYSTEM, the only way the system comes back into balance is by the temperature increasing, thereby increase the heat transfer occurring through those other means. You're example of the heat shield isn't valid because you're adding a component to the system. Sure, the temperature of the intake is reduced and the temperature of the exhaust doesn't got up much, but the temperature of the heat shield sure as heck did. The total amount of heat within the system did not change however. Regarding your house analogy, sure, if you cut a hole through your inner fender, air now has another avenue to escape, but that's a bit extreme. I wouldn't doubt for one second that it was eliminated for cost reduction purposes. My bet is still heat-soak issues related to the return-less fuel system came up and when tasked with coming up with a solution, it was a two-for-one deal to eliminate the insulation. Also consider that heat-soak occurs while the engine is not running, providing even less avenues for the heat to escape.
10-15-2021, 05:17 AM
#12
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Year: 2001 / 1999
Model: Cherokee (XJ)
Engine: Fire breathing 4 point Oh!!!
I always assumed it was part of the "Limited" trim, to have a hood liner. My Orvis XJ has the hood liner & the Orvis is higher trim than the Limited. I also assumed the hood liner helped with noise reduction.
Also, somewhere I thought I heard / read the Limited had a different carpet (thicker) than the lesser models. If that is true, I would think the thicker carpet would cut down on road noise.
Also, somewhere I thought I heard / read the Limited had a different carpet (thicker) than the lesser models. If that is true, I would think the thicker carpet would cut down on road noise.
10-15-2021, 05:30 AM
#14
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Year: 2000
Model: Cherokee (XJ)
XJ's came in a bunch of different trim levels over the years.
Go to this Wikipedia page and scroll down some.
https://en.wikipedia.org/wiki/Jeep_Cherokee_(XJ)
I can't vouch for the accuracy but figure it is close and will give you an idea of them.
Edit: I don't know why the link is not working just click on Did you mean: Jeep Cherokee (XJ)? and it will bring you there.
Go to this Wikipedia page and scroll down some.
https://en.wikipedia.org/wiki/Jeep_Cherokee_(XJ)
I can't vouch for the accuracy but figure it is close and will give you an idea of them.
Edit: I don't know why the link is not working just click on Did you mean: Jeep Cherokee (XJ)? and it will bring you there.
10-15-2021, 07:49 AM
#15
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Year: 2001 / 1999
Model: Cherokee (XJ)
Engine: Fire breathing 4 point Oh!!!
This is an example of the 1997-2001 XJ. Least optioned to most options.
- SE (example & not 100% sure, no roof rack, crank windows, etc...)
- Sport (front seats & body color coding are quick indicators of a Sport)
- Classic (front seats & body color coding are quick indicators of a Classic / Limited)
- Limited (example & not 100% sure, leather interior, little bit of wood trim, power windows & locks)
- Orvis (spoiler & fake hood vents, nicer leather trim & more wood trim)
There were also "Special Edition / Special Optioned" XJs
- 60th Anniversary
- UpCountry
- Freedom
- SE (example & not 100% sure, no roof rack, crank windows, etc...)
- Sport (front seats & body color coding are quick indicators of a Sport)
- Classic (front seats & body color coding are quick indicators of a Classic / Limited)
- Limited (example & not 100% sure, leather interior, little bit of wood trim, power windows & locks)
- Orvis (spoiler & fake hood vents, nicer leather trim & more wood trim)
There were also "Special Edition / Special Optioned" XJs
- 60th Anniversary
- UpCountry
- Freedom