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Old 14th March 2013, 22:07   #16
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Default Re: Hood Vents - Do they work in lowering temperature?

But as explained earlier in the thread it seems that the temperatures rise towards the firewall more than the other areas but that must be due to the drag effect of the hot air hitting the firewall and getting accumulated. One simple way without compromising on the structural integrity would be to install some vents or small grills along the front rain gutter to let the hot air escape up over the windshield.
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Old 15th March 2013, 00:50   #17
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Default Re: Hood Vents - Do they work in lowering temperature?

An internal combustion engine does lose heat from its outer walls, which is metal. metal is a good conductor of heat. in a jeep, the heat loss wont be as much as, say an air cooled engine with fins on it, but still, heat transfer would take place. the Under hood shape of a jeep would trap hot air , as it is less dense and accumulate it there. a vent would provide that hot air a way out and cooler air from beneath the engine bay would be able to circulate. whatever air enters the engine bay is hot anyways as it passes through the radiator. so technically, you are giving the engine some of its own heat back.

Also, heat transfer takes place faster if the difference in temperature between heat carrier and heat emmiter is large- the case with a hot engine and fresh cool air.

Some practical examples ive seen are-
1. Many buses operate with their hoods open in summer to beat the heat.
2. Ive seen extra fans being installed behind the engine of a CNG tour bus to direct the hot air away from the engine bay.
3. Tractors! they are slow, but work hard. i'm yet to see one getting over heated- and their is plenty of ventilation around the engine!
4. Super bikes- Tiny radiators, and stories of how the engine roasts the legs in slow moving traffic even if the radiator is equipped with a fan (engine is letting off heat through its body). hit the highway, the air circulates around the engine as well and the temperatures are controlled.
5. I remember reading an article in the magazine Bike India (April 2006) where a guy made a bike around a BMW 740i's V8 engine. the bike did not have enough space for the original radiator so he had to install a smaller one off a volvo. he installed two fans behind the radiator wired to the ECM, but they were never put to action as the engine was open to air instead of being shrouded by car body work.

Hood vents are worth a try i guess. nothing to lose, at least some to gain.

Last edited by dhawcash : 15th March 2013 at 00:58.
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Old 15th March 2013, 08:50   #18
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by SPIKE ARRESTOR View Post
==
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.
Plus 1 to that , perfectly tuned healthy engines ,with all systems working properly ( unblocked exhaust particularly ) should & would not overheat .

Quote:
Originally Posted by Nanometer View Post
== I remember seeing Diesel locomotive have big fans and radiators on the top , this looks like is already being put in use by Railways.
Perhaps a fan be placed under the hood vent to push the air out ? Collapsible shutters can be made above such fans when its raining hard .
Sounds good for me .

But again these are just killing symptoms , would be better to check for, if some Unscientific mods in systems are causing it ( for example non standard radiators , modified exhausts , bad timing , badly modified fuel supply lines &/or external fuel supply pumps etc )

This is a vast subject ( Air circulation around engines ) IMO , a scientific study / opinion needed .

Sudarshan

P.S. I have recently aquired a DG set & observing/ studying its shroud ( sound proof box/ canopy ) . But one thing I have observed there is , though the engine is some 3 liters , the volume of air displaced by the radiator fan is enormous ( compared to any Auto engine of similar capacity ) & it pushes hot air in reverse direction ,out of the canopy/box .

Edit : & this gives me an Idea ; what about redirecting the hot air coming in from the radiator out of the bonnet compartment & then introduce / route / force by a fan , cold ( normal atmosphere ) air in to the engine compartment from somewhere else ( via specially designed ducts ) .

Last edited by Sudarshan : 15th March 2013 at 09:00.
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Old 15th March 2013, 14:08   #19
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Originally Posted by vikram_d View Post

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.
Turbo esteems are fast. Jeeps are slow. More so when in low rrange and off roading when they heat up.
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Old 15th March 2013, 16:03   #20
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Default Re: Hood Vents - Do they work in lowering temperature?

When seeing the motorbikes and the old scooters on the road , i see there are fins all around the engine casing , why not have this done for bigger engines as well , to support the water or oil cooling systems , cooler engines give better performance or heated engines ? I remember a bus driver telling me that the AL Hino engines used to work very smooth after reaching an ambient temperature , is this the case with all diesel engines ?
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Old 15th March 2013, 16:24   #21
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Default Re: Hood Vents - Do they work in lowering temperature?

Toyota FJ-40s had louvre-like vents on the hood.

I don't think you need to be going fast for the vents to be useful. The radiator fan works hard sucking air into the engine-bay which is kind of a dead-end. The vent will allow some of the hot air to escape thereby aiding air-flow and cooling.
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Old 15th March 2013, 16:30   #22
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Nanometer View Post
When seeing the motorbikes and the old scooters on the road , i see there are fins all around the engine casing , why not have this done for bigger engines as well , to support the water or oil cooling systems , cooler engines give better performance or heated engines ? I remember a bus driver telling me that the AL Hino engines used to work very smooth after reaching an ambient temperature , is this the case with all diesel engines ?
Yes, running too cool is not a good thing. All engines have an optimum running-temperature (hence the use of thermostats in water-cooled systems).

Scooters/bikes & other air-cooled engines in general have fins to aid cooling by increasing surface area. This is not required in water-cooled engines as you out-source this function to the radiator with the water/coolant acting as a medium. There is not much point having both systems as it is better to just optimise one. Other disadvantages I can see is the fact that fins are easily broken, require a lot of airflow and are not as effective(uniform as well as outright cooling-power) as water-cooling. Water-cooling also helps reduce engine noise and vibrations due to the water-jacket.
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Old 15th March 2013, 16:57   #23
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Tejas@perioimpl View Post

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

Attachment 1061994
That vent on the W124 is an air-intake vent. The engine breathes through this. It does not throw/ excel hot air from here. This vent can only be seen on the diesel W124s

The earlier (pre-facelift) model W124s had intake from the side of the radiator. This vent came only later.

I am pretty sure that taking cool air enhances the performance of the diesel motor, but I am not too sure how much they can reduce your engine heat.
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Old 15th March 2013, 20:04   #24
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Default Re: Hood Vents - Do they work in lowering temperature?

Our Jeeps, particularly, 540/50's have large engine bays in ratio to the engines that sit in it, resulting in a 'not so packed layout'. There is plenty of room for hot air to dispel from the sides and under, since the fan and motion pressure combined flushes out the heat generated by the engine, thus 'hot air rises' principle is minimal.

There is no need for vents, since their opening would be miniscule compared to the other hot air escape routes. But, if one should go for the rear facing ones on top of the hood, rather than on the sides, it will only help in opening another route (though small) for the hot air to escape. Plus, aesthetically, something different.

It will not weaken the hood structural strength if done properly.

In my case:
An XD3P heating on long runs at speeds exceeding 80kmph, with continuous acceleration is due to the absence of a 5 forward GB

Due to the SWB dimensions of my Jeep and longer BA10, NGT520/30, Isuzu Trooper GB's which are long, rendering the propeller shaft to be reduced to under 12" and reducing articulation, not on my agenda.

Running on a smaller radiator (due to the front grill width) on a 2.5L engine translates again into a set back which had to be compensated by adding a fully functional degassing tank that helps in air cooling of the coolant and also compensating the reduced liquid capacity

Wrapping the air intake hose by a 3 layer aluminum adhesive tape, allowing cool air into the manifold.

It works, temp never crosses 70 in peak summer traffic. On long runs decelerate time to time instead of continuous and temp remains around 70. On OTR's no problem.
Regards,

Hood Vents - Do they work in lowering temperature?-jeep-003.jpg

Last edited by fazalaliadil : 15th March 2013 at 20:23.
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Old 16th March 2013, 09:23   #25
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Default Re: Hood Vents - Do they work in lowering temperature?

Extra vents in any case would permit better air flow and larger volume of air, so it is quite obvious that though the engine may not be getting cooled per se, but definitely it gives chance for a lesser ambient temperature within the engine bay and if it can add style to the bonnet and overall look of the vehicle, why not.
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Old 16th March 2013, 09:38   #26
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Default Re: Hood Vents - Do they work in lowering temperature?

Basic logic and physics says that provided the vents are not leading into ducts, the ambient temperature is lower than that of the engine and hence it must cool the engine by both sucking in cooler air and expelling warmer air. It may not necessarily cool the engine a great deal if badly designed and located, but at worst will prevent a rise in temperature.

I suggest being a bit careful with the location of the vents though. Water can enter the engine compartment through those, especially during monsoons and serious off roaring involving water bodies.
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Old 17th March 2013, 14:23   #27
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by fazalaliadil View Post
... . . .Wrapping the air intake hose by a 3 layer aluminum adhesive tape, allowing cool air into the manifold.....
WHere can I get this, and what is it called in the parts shops? Any online sellers? Want to try it on my Sx4 intake hose
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Old 18th March 2013, 07:30   #28
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Default Re: Hood Vents - Do they work in lowering temperature?

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Originally Posted by filcord View Post
WHere can I get this, and what is it called in the parts shops? Any online sellers? Want to try it on my Sx4 intake hose
Try any air conditioning and refrigeration shop, where they sell insulation material or spare parts. This is an insulation material used by them.
Regards,
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Old 18th March 2013, 10:39   #29
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Interesting compilation, btw, this query is related to Jeeps in general or a particular vehicle + engine combo ?
Query is for jeeps in general.

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Air circulation using scoops is definitely a good idea, what if it does not cool the engine, it would still look cool right ?

Spike
What is your opinion as an engineer? Is it an overkill? Looks though is just a byproduct and i'm not complaining!


Quote:
Originally Posted by dhanushs View Post
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.
Hi Dhanush, I'm not talking about the RAM air effect at higher speed. I'm asking will this work when there is no RAM air effect at lower speeds.


Quote:
Originally Posted by laxmanrk View Post
That vent on the W124 is an air-intake vent. The engine breathes through this. It does not throw/ excel hot air from here. This vent can only be seen on the diesel W124s

The earlier (pre-facelift) model W124s had intake from the side of the radiator. This vent came only later.

I am pretty sure that taking cool air enhances the performance of the diesel motor, but I am not too sure how much they can reduce your engine heat.
Thanks for that info. I never knew that. I always thought that since the petrol ones didn't have the vent, this was to dissipate heat in diesels.

Quote:
Originally Posted by fazalaliadil View Post
Our Jeeps, particularly, 540/50's have large engine bays in ratio to the engines that sit in it, resulting in a 'not so packed layout'. There is plenty of room for hot air to dispel from the sides and under, since the fan and motion pressure combined flushes out the heat generated by the engine, thus 'hot air rises' principle is minimal.

There is no need for vents, since their opening would be miniscule compared to the other hot air escape routes. But, if one should go for the rear facing ones on top of the hood, rather than on the sides, it will only help in opening another route (though small) for the hot air to escape. Plus, aesthetically, something different.

It will not weaken the hood structural strength if done properly.

In my case:
Your jeep sir is one tight machine! Hat's off.

Quote:
Originally Posted by pganapathy View Post
I suggest being a bit careful with the location of the vents though. Water can enter the engine compartment through those, especially during monsoons and serious off roaring involving water bodies.
Water i don't think sir will be an issue since the lower part of the engine bay is open anyways and there is lot of space between the front grill and radiator for water to enter during offroading and fording.

______________________

As many have mentioned that in most of the issues of overheating, we are only treating the symptoms and not the cause. Behram has been advocating the degassing tank since a long time. Have to get that done also.

What i have noticed is that (atleast in my old jeep) the engine and cooling system works flawlessly in the stock jeep. It's when we start overloading the engine by bigger tyres, power steering, AC, etc is when the overheating issue crops up.

I am trying to find a way to prevent that.

Another nice experiment and good read here:

http://www.go.jeep-xj.info/HowtoBonnetVents.htm
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Old 18th March 2013, 11:19   #30
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Question Re: Hood Vents - Do they work in lowering temperature?

Basic Questions in my mind

1) what is the Ambient temperature of an engine

a) Petrol Jeeps / Gypsy

b) All Diesel Jeeps M&M

c) All other engines ( on this forum )

2) what will be the exact overheating temperature band for each ( Petrol / Diesel ) & how to determine it ? Particularly the danger area . Do we follow the commonsense line ? ( the red band on meter ) or need to check with real figures . Whats the exact temperature ,above which certain engine will get damaged ?

No offence to anyone , but do we know the facts ? we are talking in very general ( hot / cold ) language here IMO

Sudarshan
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