Under Hood Heat

Wabujitsu

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Yep, 6 years in the Army National Guard as an MP.
Thanks for your service! 30 years FLARNG, AGR, in seven MOSs, finished my career in ADA.
 
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Bad Scott

Bad Scott

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So I decided to get sciency this morning and taped a bunch of yarn to the hood a la NASA style:
198558AB-6D4E-49C2-92AC-9B43022A921C.jpeg


Then took it for a spin down a backroad to see what happened:



It appears the center yarns are going directly at the windshield, the edge most ones are at a bit of an angle to the direction of travel, and the vent ones are even more so at an angle. My thoughts on that is there IS air coming up and out and the lowest pressure direction for it to escape is out to the sides.

Interestingly, ALL of the yarns nearest the windshield pushed down into the engine compartment which might be an indication that elevating the rear of the hood is allowing higher pressure air from the windshield to push into the engine compartment rather than allowing hot air to escape. Edit: the one that isn’t going down I pulled out to “restart the test” before I registered it was all of them like that.
94618B1F-8C1C-4405-8F11-3E60F36C9D84.jpeg


After we got the fan spinning at takeoff speeds, the yarn stayed laying down on the vents. I could feel air coming out though and wanted a better idea of how much. Jarhead mentality, if you can’t break it, light it on fire:


There is noticeably more airflow on the passenger side and I suspect (on a 2.0T at least) this is because it is alot more cramped on that side than the driver side.

My theory is the fan brings air in, and it rides along the underside of the hood and out the vent because it can’t escape down as easily. This may also be why our batteries have such a short life expectancy. If you want to cook hot dogs on your motor, on top of the battery is probably a good place.
You have a great mind!
 

J McK

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Sorry, you are incorrect. I do not want to school you on thermodynamics (Heat, Radiation, Conduction).

But, I will give you some clues; the difference between the paint on the hood and underneath the hood, the energy (Heat source) optimal operating temperature and the entropy of the material involved.

You are free to do what you feel is best for you, each to their own, but please do not claim your mod as scientific fact. It is nothing more than a cool non functional modification.
Sorry - I think you're wrong here. An insulator - the liner - will not allow heat to conduct to the hood. Instead it traps heats inside the engine compartment. All other things being equal, this will raise the ambient temperature of the entire engine compartment. Removing the liner will allow (some) heat to be conducted to the hood and dissipate to the outside - convection will probably dominate in both cases - but that doesn't make much difference. More heat will be transmitted to the outside than if the liner is in place. How much of a difference this will make remains to be seen - it requires a careful measurement with a thermocouple - so far as I know, no one has reported results on this so far.

I can't speak to the paint issues. But would argue that repainting the hood every few years beats replacing an engine. Also would argue that I'm not sure that the engine gets the hood much hotter than the AZ sun in July. ;)

FWIW - heat dissipation from the engine bay IS an issue for diesel owners. Overheating is well known to cause automatic de-rating of engine performance during normal highway driving at high temps & altitude (aka summer driving in AZ & UT!) This is especially a problem for Gladiator owners when towing loads (within the spec) as the heat load is even higher. You can read the latest conclusions here:

https://www.jeepgladiatorforum.com/forum/threads/diesel-cooling-options-and-ideas.46298/page-21

Short answer: the best bet seems to be to use the Tazer JL Mini to re-program the radiator fan and flip it on when entering a high heat load situation. Best long term fix will probably be an aftermarket oil cooler - but none is available at the moment.

Note that air scoops don't seem to help much - probably because there isn't much airflow over the surface of the jeep hood - see aerodynamics of a brick. (This could also help explain why removing the hood liner has such a small impact). That said - fender liner vents and the rear facing hood vents discussed above do look promising - but again - not much hard data is available. Oil & radiator temps are good to know - but you really want to see what's happening in the compartment...

I expect to make some or all of these mods over the coming months. My hope is to make the mods systematically so I can see the impact of each change. Will post the data - good, bad or indifferent.
 
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Bad Scott

Bad Scott

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I found these 12V water & dust proof mini fans online (see attached). I wonder if an evacuation duct could be used with these fans and routed through the side vents (see attached) to dissipate heat and relieve pressure under the hood
Fan.JPG
Inner Fender.JPG
?
 

BDinTX

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Those look like cooling fans for a PC, not sure they are intended to operate in an engine compartment but I like where you're going. I think we need to reduce back pressure in the engine compartment. In the gladiator forum thread somebody pointed out there should be a seal between the bottom of the radiator and grill to help direct air through the radiator rather then under it. That also sounds like a reasonable addition.
 

Windshieldfarmer

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Has anyone set up thermometers in various parts of the engine bay to measure before and after results? It goes to reason that high heat could prematurely wear out engine plumbing components though I doubt the impact would affect engine or transmission longevity. If under hood high heat was a big concern Mopar would not offer an extended Max Care warranty.
 

jbcrane

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OK, so I'm the new kid and I just read through (almost) every post in this thread. I have a question: does anyone else regularly open their hood when done driving to allow all that pent-up heat to dissipate more quickly? I started doing it on my last car after it developed cooling issues and the habit has carried over to my new Wrangler. I'm convinced it's a good thing to do. I've noticed that despite the mid-to-high 90's we've regularly seen around here this summer - he runs perfectly cool. That's not the issue. When I pull him in the garage his hood is often cooler to the touch than about 15 minutes after I've parked. All that heat under the hood while he's running down the road is being addressed by the engineering designed to keep him cool. But when he stops, so does the cooling. So opening the hood allows all that heat to escape more quickly, saving wear and tear on the plastics, rubbers, computer chips and everything else over the life of the engine bay. The prop gets pretty hot, so I have an axe handle I keep by the front and open him up to give him some air when done driving. I know I probably don't need to, but it feels like a good thing to do. Not saying every time, everywhere... but.... Don't want my buddy ridden hard and put away wet when there's an easy fix. Anyone...?
Open Hood.jpg
 

Mikester86

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OK, so I'm the new kid and I just read through (almost) every post in this thread. I have a question: does anyone else regularly open their hood when done driving to allow all that pent-up heat to dissipate more quickly? I started doing it on my last car after it developed cooling issues and the habit has carried over to my new Wrangler. I'm convinced it's a good thing to do. I've noticed that despite the mid-to-high 90's we've regularly seen around here this summer - he runs perfectly cool. That's not the issue. When I pull him in the garage his hood is often cooler to the touch than about 15 minutes after I've parked. All that heat under the hood while he's running down the road is being addressed by the engineering designed to keep him cool. But when he stops, so does the cooling. So opening the hood allows all that heat to escape more quickly, saving wear and tear on the plastics, rubbers, computer chips and everything else over the life of the engine bay. The prop gets pretty hot, so I have an axe handle I keep by the front and open him up to give him some air when done driving. I know I probably don't need to, but it feels like a good thing to do. Not saying every time, everywhere... but.... Don't want my buddy ridden hard and put away wet when there's an easy fix. Anyone...?
Open Hood.jpg
I picked up the same habit after seeing my brother in law so this with his Corvette. Jeeps in garage with hood up as I type this.
And yes, a whole lot of heat is released.
 
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Bad Scott

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OK, so I'm the new kid and I just read through (almost) every post in this thread. I have a question: does anyone else regularly open their hood when done driving to allow all that pent-up heat to dissipate more quickly? I started doing it on my last car after it developed cooling issues and the habit has carried over to my new Wrangler. I'm convinced it's a good thing to do. I've noticed that despite the mid-to-high 90's we've regularly seen around here this summer - he runs perfectly cool. That's not the issue. When I pull him in the garage his hood is often cooler to the touch than about 15 minutes after I've parked. All that heat under the hood while he's running down the road is being addressed by the engineering designed to keep him cool. But when he stops, so does the cooling. So opening the hood allows all that heat to escape more quickly, saving wear and tear on the plastics, rubbers, computer chips and everything else over the life of the engine bay. The prop gets pretty hot, so I have an axe handle I keep by the front and open him up to give him some air when done driving. I know I probably don't need to, but it feels like a good thing to do. Not saying every time, everywhere... but.... Don't want my buddy ridden hard and put away wet when there's an easy fix. Anyone...?
Open Hood.jpg
I love people who think out-of-the-box!
 

jbcrane

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I love people who think out-of-the-box!
After the first few times burning my fingers trying to unclip the prop from the (cheap) yellow, plastic retainer I knew there had to be a better way. This ax met an untimely end late last year and after a good shellac and a few beers, we’ll… everyone likes to feel useful.
 

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Haha, pull the liner, the horse shoe engine cover and raise the hood hinges. What's the old saying,
"you can lead a horse to water but you can't make it drink".
 
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