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-   -   Hood Vents - Do they work in lowering temperature? (https://www.team-bhp.com/forum/4x4-technical/133711-hood-vents-do-they-work-lowering-temperature.html)

There have been many threads about our jeeps overheating all over the forum.

A few of them:

http://www.team-bhp.com/forum/techni...blem-jeep.html

http://www.team-bhp.com/forum/4x4-te...r-heating.html

http://www.team-bhp.com/forum/4x4-ve...eam-bhp-7.html

http://www.team-bhp.com/forum/4x4-ve...w-mm540xd.html

http://www.team-bhp.com/forum/4x4-ve...y-mm540-6.html

http://www.team-bhp.com/forum/4x4-ve...offing-13.html

The usual suggestions to counter the problem are:

- flush radiator

- clean radiator

- check for leakages

- check radiator cap seal

- check water pump

- check gaskets

- radiator upgrade

- install electric auxiliary fan

- fan shroud

- get a fan with more leaves

- remove bug screen for getting more airflow

- don't over stress engine by AC/speeding on ghats/overloading/towing/etc

- remove thermostat (?)


What else?

While researching more for my new jeep build, i chanced upon hood vents.

I've seen earlier diesel cars had vents like this old merc:



Or performance cars:



Ofcourse not all newer diesels sport vents.

But, i'd never seen on our jeeps till now. And with older engine that they had, it made sense theoretically to have them.

The staggering amount of results that a simple google search on this topic gives you, made me delve a bit deeper into the subject.

A little more research led me to many forums. I became a member there and started interacting with people who've done it on their rides.

Here are some pics off these forums:

Rationale:

Let hot air escape rather than allow cold air to enter or both?

Rather than physically cool the engine, it allows the engine to work more efficiently thereby preventing overheating.

Advantages:

- lowering temperatures

- Its a cumulative benefit on top of other mods IMO. Getting rid of that trapped hot air preserves parts, wiring and in general, eliminates some of the heat sink into the tub. (Robert J. yates - jeepforum.com)

- power gain (?)


Testimonials

30° Fahrenheit is ~ 16.6° Celsius using a formula from Wiki.

180° F ~ 100° C & 150°F ~ 83.3° C

Possible Cons to Hood Vents:

- Heat damaging paint as told by a member of jeep forum.com

- weaken the strength of the panel (?)

- Rain getting in. Solution: install a rain gutter

- water getting in while pressure wash. Solution: keep vent position away from fuse boxes, battery, etc


Points to ponder:

- For good circulation, louvres would work better than vents

- if water running through an engine can't cool it, how will cooler air over it do it?

The opponents of vents say that it just prevents fading of the paint over the bonnet rather than lowering temperatures.

Another option to reduce temperature:

50° F ~ 27.7° C


Here's a pic of a wrapped intake of member TJeeper from jeep forum.com:

A few DIY threads:

http://jeepsunlimited.com/forums/sho...d.php?t=507801

http://www.jeepforum.com/forum/f9/ge...05/index2.html

http://www.jeepforum.com/forum/f46/d...-hood-1182548/

http://www.stu-offroad.com/body/hood...odlouver-1.htm

Can i use a hood scoop like the ones used to feed air to the intercooler?

NO, unless mounted in reverse direction.

Experiments and good reads:

http://jeepsunlimited.com/forums/sho...ght=hood+vents

http://www.oman4x4.com/hoodvents.htm (has part of above text quoted, but with pics)

Going through the pros and cons, i'm still not 100% convinced, but having said that, i'm still going to experiment with the wrap and hood vents (holes on the side of the hood) in my jeep.

Why aren't you convinced? They will definitely work provided the vents are placed facing the cabin like shown in the one of the photos with the vehicle having multiple louvers on the hood.

As far as weakening of the hood is concerned, I'm sure welding a few small strengthening bits near the vents will solve the problem.

A friend of mine had found a very simple solution for his over heating turbo esteem. On the esteem below the hood there is a rubber beading which prevents rain water rolling off the wind shield from entering the engine bay. His solution was to simply remove that beading and create a small air gap along the width of the hood for hot gases to escape. While the car was moving, the hot air would escape through this gap and flow over the wind shield. Simple, ingenious and super effective. This air gap was only about 4 - 5 mm but still it worked wonders.

Well, let me rephrase. I'm not convinced that they would lower the temperature, rather they would prevent or delay the rise in temperature IMO.

I'm going to make 2 holes on either side of my jeep bonnet. Was advised against slits for the structural integrity issue since many times, we do stand on the bonnet of the jeep.

They will lower the overall temperature inside the engine bay as there will be constant air flowing through it. The effect of this air flow would be that the existing cooling system would be super efficient as it does not have to work very hard to keep the engine at optimum operating temperature and also less chances of engine overheating.

Edit: You have also mentioned that if water cannot cool the engine, how can air? Well, water also needs air to cool and hence we have the radiators and cooling fans. Air cools water cools engine. :)

Yes removing hot air from inside the cabin should cool the engine. Further in many cars there is a carpeted mold attached to the underside. During summers if one was to remove it and let the heat dissipate through the metal sheet itself, would it help or increase the temperature even more due to the heating effect of the sun onto the metal hood? I think during movements it would cool but fry up the insides of a parked vehicle.

Hi,

I am no expert in this, but was told that the reason the CJ3B has vertical vents below the mudguard was to dissipate the head from with the engine bay. The way it works is simple, when the vehicle is in motion ambient air flows over the vents creating a vaccum over the vents therby ensuring the air gets sucked out from within the engine bay. If you look at any CJ3B you will notice air vents behind the front tyres. The guy who told me this could be pulling the wool over my eyes.

Vijay

Wow what a informative thread !! especially in the jeep case the vents is a must. Because the the air flow will be very high on a performance Diesel Jeep in off road ( air flow will be high in 4L:Frustrati).

What is the root reason of over heating of a Jeep Engine ? Mainly DP & XD3P ? why Di/MDi is not over heating as XD3P ? its should have been too easy to add a air vent to prevent a Engine rebuild :uncontrol.

Interesting compilation, btw, this query is related to Jeeps in general or a particular vehicle + engine combo ?

Sreejesh, Jeeps overheat due to various reasons. The easiest workaround we see these days is to add a bigger radiator, which treats the symptom and not the cause.

Air circulation using scoops is definitely a good idea, what if it does not cool the engine, it would still look cool right ?;)

Spike:D

Tejas, hood vents, as long as they are properly designed, ie, they dont hinder the normal flow of air, but only add to it, definitely make a difference, and there is no doubt about it. However my take on these is:

• Hood Vents are helpful as long as there is Ram Air. And for Ram Air to be helpful, the speeds should atleast be 40+ kmph (?).

Now, considering the fact that most of our Jeeps overheat while off-roading/load carrying and not(mostly) on-roads, I doubt the practicality of this mod in reducing the engine temperature.

However:

• Hood Vents only help, and do not do any harm (if properly placed and designed).
• They look good.
• There is a small fraction of jeeps(like mine) which overheat when you travel @100kmph for more than 10-15 minutes. These would definitely help them.

Yes, I think they might have an impact on the structural integrity. However, like vikram mentioned, you should be able to find a way around.

My Take: Yes, Hood Vents are worth a try.

This a interesting topic, i would say that its simple science on convection ,hot air rises high and needs to escape through the vents you should have vents or holes on the bonnet or check the air flow in a wind tunnel and come out with the correct position of those vents . I remember seeing Diesel locomotive have big fans and radiators on the top , this looks like is already being put in use by Railways.