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Old 18th March 2013, 11:37   #31
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Default Re: Hood Vents - Do they work in lowering temperature?

Very correct and logical thinking sir.

I'm talking about the red band here. I guess every engine will have it's own ambient running temperature and would also be affected by outside atmospheric pressures (?).
This data i presume would only be available with the manufacturer.
Therefore, i guess matching the OE meter to the engine is important and as well as selecting the right thermostat for the engine.

Older cars atleast had a meter which we could keep an eye on as the temperature rose. Never petrol and diesel vehicles just have a light that comes on indicating overheating.

Having said that, if we did know the ideal temperatures, we could be better informed.

EDIT:
An example: in my classic i would be happy when the jeep was running ~80C. When the temp rose between 80~85, alarm bells would go off in my mind and i would keep one eye on the meter and slow down and as soon as it climbed above 85C, i'd probably pull over to access the situation.

Last edited by Tejas@perioimpl : 18th March 2013 at 11:41. Reason: see edit
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Old 18th March 2013, 11:45   #32
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Tejas@perioimpl View Post

Having said that, if we did know the ideal temperatures, we could be better informed.
Lets ask experts on board ( BHP ) , I know few people will certainly know & help , Arka ,Sutripta Da , SS Da , Ken , DB Sir ??

for a start I remember seeing the xdp thermostat embossed with '68' . Is that the ambient temperature or the full open one for the unit ?


Sudarshan

* Edit : I have run the xdp at around 100 for many times in all these yrs -- never cracked head or lost a gasket . my current Landy overheats & has forced me to run at & around 100 regularly ( on local gaskets ) no Issues ; sometimes I think the mechs are not using torque wrenches & figures to support while doing the job ( I do that without fail )

Last edited by Sudarshan : 18th March 2013 at 11:50.
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Old 19th March 2013, 21:43   #33
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Default Re: Hood Vents - Do they work in lowering temperature?

Another thing to consider, with using a petrol engined jeep as an example.

A good reason to keep the engine bay cooler and air intake insulated on a petrol jeep, is to lower the temperature of the intake charge.The reason for this is if you can keep the ambient temp of the intake charge lower you can effectively have a larger volume of air(hot air expands) in the manifold to mix and atomize the fuel thus adding more hp.this is probably why lower under hood temperatures might add a few hp on a big 3litre V6 petrol engine.

A Naturally aspirated diesel engined jeep(mm540/550) might benefit from this but to a lesser degree as the fuel is directly injected into the cylinder and does not have to mix with the incoming air in the manifold like a carb or port injected petrol engine to be stoichiometrically correct.If you use a snorkel the engine is ingesting cooler air anyway.There are better ways to reduce engine temperature and improve performance.

I feel the louvres or vents on most vehicles are more for the asthetics.unless it is feeding a intercooler as mentioned earlier or a really high performance engine where it makes sense to use every trick you can to increase efficiency.
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Old 19th March 2013, 22:19   #34
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Default Re: Hood Vents - Do they work in lowering temperature?

In order to quantify the effects of colder air entering the engine there are a few rules of thumb:


Considering only the relationship of intake air temperature to HP, the power varies essentially as the square root of the change in ABSOLUTE temperature. So you need to convert your degrees centigrade of Fahrenheit to Kelvin

For instance a 2 liter engine develops 130 HP at 59 deg F which = 15 deg C, this represents 288.15 deg K on the Celsius absolute temperature scale. To calculate change in HP, take the square root of the quotient of the standard temperature (288.15 deg K) divided by the proposed temperature in deg K and multiply that by130.

For example:
What is the HP output at 30 deg F (-1.11deg C) where the absolute temperature is 272.04 deg K?
1. Divide 288.15 by 272.04= 1.059
2. Take the square root of 1.059=1.029
3. Multiply 130(1.029)=133.8 HP


In the same manner some other representative temperatures are:
100 deg F=37.78 deg C=310.93 deg K=125.1 HP
140 deg F=60 deg C=333.15 deg K=120.9 HP

You could also just plug in some numbers in this little handy convertor:

http://wahiduddin.net/calc/calc_hp_dp.htm

So you can see that roughly a 20 - 30 degree centigrade drop in temperature might give you a 3-4% gain in Horse power. Unless you're a F1 driver you wouldn't notice!

So, yes these hoods and other methods do work. But the math clearly shows that the expected gain is really very little for us ordinary drivers to notice. if you're drag racing, a NASCAR driver or rally driver these small advantages become very useful, if not critical. But for us run of the mill drivers I don't believe it does anything useful. Maybe a nice Saturday afternoon tinkering with your car, very enjoyable and you should absolutely do it! And after having spent the time and money on parts I'm sure you'll be convinced there is a noticeable improvement. Sadly, its probably more wishful thinking then reality.

Keep tinkering with those engines! It's a great way to spent your weekend. I know I do. And I keep telling me wife that I'm improving the performance. She doesn't believe me either, but she loves me still, so it doesn't matter. As long as I'm happy she's happy for me too. Nothing factual, just perception, wishful thinking and a 30+ year marriage.

Jeroen
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Old 19th March 2013, 22:34   #35
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Tejas@perioimpl View Post
Very correct and logical thinking sir.

I'm talking about the red band here. I guess every engine will have it's own ambient running temperature and would also be affected by outside atmospheric pressures (?).
This data i presume would only be available with the manufacturer.
Therefore, i guess matching the OE meter to the engine is important and as well as selecting the right thermostat for the engine.

Older cars atleast had a meter which we could keep an eye on as the temperature rose. Never petrol and diesel vehicles just have a light that comes on indicating overheating.

Having said that, if we did know the ideal temperatures, we could be better informed.

EDIT:
An example: in my classic i would be happy when the jeep was running ~80C. When the temp rose between 80~85, alarm bells would go off in my mind and i would keep one eye on the meter and slow down and as soon as it climbed above 85C, i'd probably pull over to access the situation.
Hood vents work in principle, but it may not be the culprit/biggest offender...which is what you need to identify and treat first.

I take it your jeep has an engine driven fan?? does it have a fan shroud? Has the block been flushed? What is the state of the water pump? Has it been overheating from day1 ?

Last edited by Mpower : 22nd March 2013 at 20:45.
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Old 19th March 2013, 22:40   #36
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Default Re: Hood Vents - Do they work in lowering temperature?

My new jeep is still in the works and i've not had any overheating issues during testing.
I'm trying to pull out all tricks to prevent it from happening.

My old classic had overheating issues and that issue was discussed over multiple pages in my thread and finally was solved by replacing a faulty radiator cap (as diagnosed by Mr Behram Dhabhar)
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Old 19th March 2013, 22:50   #37
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Tejas@perioimpl View Post
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.
Tejas, in that case, my answer would be NO DIFFERENCE.

Because:
  1. The snorkel would anyhow pull in cold air, so, no point in having the vents to pull in a 'lil bit of colder air intake.
  2. Our ol' Jeeps generally have enough space in the engine bay, and huge 'openings' near the firewall to let the hot air flow out. So, the ambient temperature drop of the engine bay, by having vents would not be much, considering their effect in reducing the overall engine coolant temperature.
  3. The radiator fan, in OE form (without the insect mesh) has enough space/opening to pull in air. Hence there too, we don't need a vent.

On a lighter note: I might remove the 4 + 4 nut/bolts holding the bonnet, and have a particularly harsh ride with the bonnet less Jeep. Will solve the questions once and for all!
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Old 19th March 2013, 23:45   #38
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Quote:
Originally Posted by dhanushs View Post
[*]and huge 'openings' near the firewall to let the hot air flow out.
Why does it have openings at the firewall? My jeeps are sealed as tight as possible at the firewall. Why let warm engine air invade the cabin?


Quote:
Originally Posted by dhanushs View Post
[*]The radiator fan, in OE form (without the insect mesh) has enough space/opening to pull in air. Hence there too, we don't need a vent.
Again, we are discussing letting hot air out and not about air coming in.


Quote:
Originally Posted by dhanushs View Post
On a lighter note: I might remove the 4 + 4 nut/bolts holding the bonnet, and have a particularly harsh ride with the bonnet less Jeep. Will solve the questions once and for all!
Lol. But never do that even as a joke. The bonnet provides a lot of protection to the engine bay from rain, debris, etc.

OT: Btw, how will removing the bonnet make the ride harsh?


Edit: everyone, please don't get me wrong, I'm not arguing here for or against vents.

I do not understand the advanced mechanics of engines etc very well and I try my best to research the matter as I did in this case but still couldn't find any conclusive data and thus I formed this thread. I'm not afraid to ask if I don't know but am looking for scientific and / or proven feedback along the lines that motocamp, or jeroen just provided.

Last edited by Tejas@perioimpl : 20th March 2013 at 00:06.
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Old 20th March 2013, 00:25   #39
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Tejas@perioimpl View Post
Query is for jeeps in general.
Ok.

Quote:
What is your opinion as an engineer? Is it an overkill? Looks though is just a byproduct and i'm not complaining!
In my opinion not worth the effort, concentrate more on the mechanicals rather than such things, will yield you more benefits.

Quote:
Originally Posted by Sudarshan View Post

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 ? we are talking in very general ( hot / cold ) language here IMO
Very well said, some temperature values will help. Thermocouples anyone?

Quote:
Originally Posted by Tejas@perioimpl View Post
Very correct and logical thinking sir.

I'm talking about the red band here. I guess every engine will have it's own ambient running temperature
Having said that, if we did know the ideal temperatures, we could be better informed.
Exactly, well said !

Quote:
Originally Posted by Jeroen View Post
In order to quantify the effects of colder air entering the engine there are a few rules of thumb:


Considering only the relationship of intake air temperature to HP, the power varies essentially as the square root of the change in ABSOLUTE temperature.
Sir, could you explain more about this relation?

Spike
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Old 20th March 2013, 07:04   #40
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Default Re: Hood Vents - Do they work in lowering temperature?

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Originally Posted by SPIKE ARRESTOR View Post
Sir, could you explain more about this relation?

Spike
Spike,
See my earlier post where I made that statement. I gave a few calculation examples:

Shows for instance for a given motor rated at 130HP at 15oC, when the temperature drops to -1oC the HP increase to about 134HP.

So it's really about how much does a hood vent lower the temperature. A 20oC drop is probably already on the optimistic side. Never the less, it does work, only a bit.

There are a few other things to consider which are also beneficial and have been mentioned by other members already. Such as having somewhat cooler air circulating around the engine and its components. Some cars have a tendency to overheat and this might help a bit. And of course, on some cars these hood vents can look pretty cool!

Here in India with all the dust I would think that cleaning your air filter very regularly, maybe investing in a free flow filter, gives you more benefits (read power) than the hood vents. And is probably cheaper and much easier to install. But then again, we love tinkering with our cars!

Jeroen
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Old 20th March 2013, 08:18   #41
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Default Re: Hood Vents - Do they work in lowering temperature?

Quote:
Originally Posted by Jeroen View Post
I gave a few calculation examples:

Shows for instance for a given motor rated at 130HP at 15oC, when the temperature drops to -1oC the HP increase to about 134HP.

Jeroen
Hi there.

Do the above rule of thumb calculations work for both Petrol and Diesel engines?

In a NA Diesel engine,which most of the Jeeps here are, is air intake temperature as critical to overall engine operating temperature and /or Power output, as compared to fuel injection?

Wouldn't a lean running diesel run hot irrespective of air intake temperature?

Cheers
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Old 20th March 2013, 08:50   #42
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Default Re: Hood Vents - Do they work in lowering temperature?

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Originally Posted by gthang View Post
Hi there.

Do the above rule of thumb calculations work for both Petrol and Diesel engines?

In a NA Diesel engine,which most of the Jeeps here are, is air intake temperature as critical to overall engine operating temperature and /or Power output, as compared to fuel injection?

Wouldn't a lean running diesel run hot irrespective of air intake temperature?

Cheers
Very good question. I'm still pondering this question. The "rule of thumb" works for NA petrol engines. As soon as you add a turbo or supercharger it all become very different of course.

I'm pretty sure that the basic effect of cooler air will have a similar effect on NA diesels. However, I would think that the effect is much less and that it will only work in more 'narrow' band of temperature. Especially lower ambient temperatures when you go below 0oC will introduce other effects.

At extreme low temperatures diesels might have difficulty, for at least two reasons. Diesel are very efficient and they tend to lose heat under very low temperature conditions. (e.g. my VW TDI engine could take 20 -25 minutes to heat up properly in winter conditions in the Netherlands)

Also there is a noticeable effect of inlet air temperature on how well diesel self ignites. The lower the poorer basicly. If you google for some information you will find very little. There are a number of articles out theres explaining the effect of air inlet temperature on marine diesels. They are nearly always supercharged.

So I don't have an exact answer. Gut feeling is that you're probably correct. In practice it's very likely to be a very small effect.

Not mentioned in this thread I believe, but the lower (ambient) temperatures create other effects as well. For all the reasons it creates a few more HP on NA Fuel engine it also increase drag. Colder air has higher density. If you're offroading stuck in a jungle that aerodynamic drag isn't a factor, but a few additional HP is nice to have.

So really to quantify the effects is pretty complex.

My statement that cleaning your air filter regularly and/or replacing it with a free flow filter is likely to give you more benefits here in dusty India holds true for NA fuel and diesel and turbo/supercarged fuel and diesel alike!


Jeroen

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Old 20th March 2013, 09:43   #43
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Default Re: Hood Vents - Do they work in lowering temperature?

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Originally Posted by Jeroen View Post
I'm pretty sure that the basic effect of cooler air will have a similar effect on NA diesels. However, I would think that the effect is much less and that it will only work in more 'narrow' band of temperature. Especially lower ambient temperatures when you go below 0oC will introduce other effects.

Yeah, I feel the same as well. And less of an effect here in India where ambient temperatures are usually quite high.

Have a feeling the habit of setting fuel pumps for "Maximum Mileage" is one of the major contributing factors to overheating here in India.

Would like to know if any have altered settings and noticed any difference.

Cheers.
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Old 20th March 2013, 10:56   #44
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Default Re: Hood Vents - Do they work in lowering temperature?

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My new jeep is still in the works and i've not had any overheating issues during testing.
I'm trying to pull out all tricks to prevent it from happening.
From what little experience I've had with the 14B, overheating isn't an issue as long as the radiator fins aren't packed with mud and the rest of the cooling system is working!

I must've done about 4000 kms on the 14B so far and have not had the temperature exceed 85-90. The one exception though was at night driving back non-stop from Mcube that the temperature went up to 100+ but then I realized that if I switch off the headlights the temp needle would fall back to the 85-90 range . Unfortunately, this thread won't solve that problem!

In any case, DI engines are less prone to overheating, at least my mechanic says so...

Unfortunately, most of us have dealt with a Peugeot engine in the past and hence we suffer from this. Maybe we should just call it Jeep-Induced Thermophobia

Cheers,
Adi
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Old 20th March 2013, 11:37   #45
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Default Re: Hood Vents - Do they work in lowering temperature?

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The one exception though was at night driving back non-stop from Mcube that the temperature went up to 100+ but then I realized that if I switch off the headlights the temp needle would fall back to the 85-90 range .
Hey Adi,
Strange, but that is exactly the problem i've faced with my Gypsy too.
I initially thought that it is some grounding issue. But it isn't.
Does this mean that, due to the lights on, the load from the alternator leads to the temp increase?
Cheers,
Deepak
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