Bonnet vents

[TheStig]

Just wondering what everyone's thoughts are on my bonnet scoops.
Cheers

[rangietragic]

Not bad:)

[Tombie]

May I ask why you fitted them?
And what engine you have?

[redrovertdi]

if any hot air comes out it will blow in through open windscreen flaps, i would have them facing the other way and add a vent on the side guard [opposite side to snorkel][thats what i did any way and thermo fans push that air out the side]

[TheStig]

I have a td5 and I did it to release all the hot air as one is located almost ontop of the turbo (and for the looks) .. I didn't have them facing the other way because when it rains the engine bay would get satched.

Thanks for the feedback

[TheStig]

Oh I'm also looking at getting a side vent as well.

[uninformed]

I think they look horrible. I think the negatives outway the positives. I know a simple side guard vent does the job more than enough.

[TheStig]

I think they look horrible. I think the negatives outway the positives. I know a simple side guard vent does the job more than enough.



What are these other negatives besides looks (in your opinion) and the positives ??
Cheers

[mudder110]

hi all quick question probably been asked before, ive all ways let my 300tdi idle for about two or three minutes.before I drive off.
longer in winter its got 355,000ks up uses no oil, am going around Australia next year
is letting it idle to warm a bad idea? was contemplating a rebuild did replace the head gasket at 220,000 advice appreciated cheers

[TheStig]

I think they look horrible. I think the negatives outway the positives. I know a simple side guard vent does the job more than enough.



What are these other negatives besides looks (in your opinion) and the positives ??
Cheers

[AndyG]

Those vents are not my thing, but been tempted by the more subtle fluting.
At high speed nothing due to pressure zone, at low speed, or stationary in the heat, heat goes upward, so it has to help.

[manic]

I don't think it looks bad.

The bonnet is usually sound insulated so cutting holes in the top will send revs through your windscreen. Then there's the rain water dripping into your engine bay when its parked up.

Apart from looks I can't think of any reason why you would put vents in the bonnet instead of the side wings.

[wrinklearthur]

hi all quick question probably been asked before, ive all ways let my 300tdi idle for about two or three minutes.before I drive off.
longer in winter its got 355,000ks up uses no oil, am going around Australia next year
is letting it idle to warm a bad idea? was contemplating a rebuild did replace the head gasket at 220,000 advice appreciated cheers

I always move off steady and let the engine warm up on the road. But I don't load it up too much until the engine reaches it's working temperature.

The only time a engine needs to idle for a while after starting ( that's to warm the oil before moving off ), is when the air temperatures are really cold or below freezing IMHO.
.

[wrinklearthur]

To reduce the heat in a Defender cab that has not any airconditioning, how effective is the side vent in dumping some of the heat?
.

[TheStig]

I don't think it looks bad.

The bonnet is usually sound insulated so cutting holes in the top will send revs through your windscreen. Then there's the rain water dripping into your engine bay when its parked up.

Apart from looks I can't think of any reason why you would put vents in the bonnet instead of the side wings.


Na my bonnet never had insulation, I got it mostly because I like the look of it.
I am putting in a side vent as well.

[Steve Td5 130]

Hi All

Saw a Defender Td5 a few weeks ago
Wearing a standard to small Subaru Wrx bonnet scoop
positioned towards the back of the bonnet just in front of the ridge in the bonnet.

Pulled up and had a quick chat with the gentlemen
He told me he did it to help push cool air down the front of the firewall which helps the air conditioning to work more effectively and push the heat from the engine bay out under the car.
He also said that according to the computer the engine is running between 3 - 6 degrees cooler on the open road due to better air flow.
The other advise he gave me was to put heat shield ( dynamat ) on the floor panels to reduce the heat coming up through the floor.

Cheers

Steve

[joel0407]

I like the idea of side vents but I'm cautious.

Some manufactures go all out to design engine bays and the air flow through them. Small changes can make big differences. Doing it wrong can have a negative effect. I know that the bull bar is probably the biggest negative thing I have done to mine but I don't want to make it worse by adding side vents than might reduce the air being drawn down under the vehicle.

As an example of negative effect. Those full width mud/stone flaps that people often put across the rear of vehicles to stop stones and mud being thrown up over the trailer/caravan are known to increase diff and transmission temps as the the air pressure in increased in front of the flap and air flow reduced.

Vehicle aerodynamics are bloody complicated.

Happy Days.

[Tombie]

Look at the gap between bonnet and guards - no need for vents on there at all - especially on a diesel..

However, if you like the look that's your prerogative.

[dobbo]

I like the idea of side vents but I'm cautious.

Some manufactures go all out to design engine bays and the air flow through them. Small changes can make big differences. Doing it wrong can have a negative effect. I know that the bull bar is probably the biggest negative thing I have done to mine but I don't want to make it worse by adding side vents than might reduce the air being drawn down under the vehicle.

As an example of negative effect. Those full width mud/stone flaps that people often put across the rear of vehicles to stop stones and mud being thrown up over the trailer/caravan are known to increase diff and transmission temps as the the air pressure in increased in front of the flap and air flow reduced.

Vehicle aerodynamics are bloody complicated.

Happy Days.

Its shaped like Lego. A standard 110 has the aerodynamics of a house brick. Besides could a 110 achieve a top speed to benefit from any aero kit?

Sent from my ZTE T809 using AULRO mobile app

[manic]

.... but I don't want to make it worse by adding side vents than might reduce the air being drawn down under the vehicle.


Talking defenders here. Don't think you need to worry about that. Below the bulkhead is pretty much below the bumper - in full wind. Steering guards, diff guards, under body protection would all have more effect on air passing under the vehicle and those go on without warnings.

On a defender vents in side wings will facilitate air through your rad, into your engine bay and out again. All good. Simples.

[Barefoot Dave]

A simple manometer will confirm any thougthts about vent placement.
Manometer；an air pressure reading device.
DIY. Grab a soft drink bottle and half fill it with water and some food colouring
Get 3m of clear plastic tubing about 3-4mm ID.
A bit of stick taped to one end of the tube with cm marked on it then stick the tube/stick into the bottle of water.
Tape the free end of the tube in the location you want to test. Tape it perpindicular to the direction of travel to avoid false readings.
Go for a drive at highway speeds to get a +or-ive reading.
Use a helper to take readings so you can just drive. Be safe.
For heat extraction move it around until you find the lowest reading.

As for water ingress, it is a land rover designed to drive through water isnt it?
If you are really worried about a few drops of water, then place a flat 'S' shaped water trap under the vent.
Even a Defender has had some thougt go into heat transfer. Why is there a heat shield on the turbo?
The hot air is drawn down the back of the engine at road speed into the low pressure zone under the car.

[uninformed]

Wool pile test is another easy way. It has been done by a member here with a 2 inch lifted defender. That and his knowledge helped me with my vent placement. Avoiding bonnet area. Top of guard would be ok for intake, but as has been discussed many many times, air is already damming up in a stock defender engine bay. If you want more flow through your ic and rad you need to get it out first.

I was also able to confirm side guard vent working on another mates defender at speeds from 0-70km/h.

My engine temps on my vdo gauge also confirmed it when I had cut it out.

[AndyG]

By side guard, i assume we are talking into wheel arch area?

and if i was concerned about temps, my first action would be to wrap the exhaust prior to chopping holes in bodywork, IMHO.

[manic]

Exhaust wrap is a good idea.

You do not have to 'chop holes' in the bodywork, over the years defenders have come out the factory with apertures left and right. You can get these panels from scrap, order in new aluminium or even plastic panels. With your air intake redirected to one of the top wing vents or a southdown snorkel you can have a 'factory' side vent on each side, improving the flow of air through your rad and out of your bay. This is the way I'm going ..... eventually..... or maybe never :wheelchair:

[Jeff]

Some manufactures go all out to design engine bays and the air flow through them.
...
Vehicle aerodynamics are bloody complicated.

I don't think the 'a' word has been used on the Defender part of the forum before :p

I don't think Land Rover put much effort in at all designing the Defender, just took existing bits, added a stripe and voila.

Jeff

:rocket:

[PAT303]

hi all quick question probably been asked before, ive all ways let my 300tdi idle for about two or three minutes.before I drive off.
longer in winter its got 355,000ks up uses no oil, am going around Australia next year
is letting it idle to warm a bad idea? was contemplating a rebuild did replace the head gasket at 220,000 advice appreciated cheers

I've been doing that for 16 years and at almost 470,000k's mine doesn't use oil or coolant,the nay sayers have been saying it'll glaze the bore but I think my motor knows best. Pat

[Didge]

hi all quick question probably been asked before, ive all ways let my 300tdi idle for about two or three minutes.before I drive off.
longer in winter its got 355,000ks up uses no oil, am going around Australia next year
is letting it idle to warm a bad idea? was contemplating a rebuild did replace the head gasket at 220,000 advice appreciated cheers
here's a link to a thread discussing the problems with letting diesels idle for too long - apparently it causes the bore to glaze.

http://www.aulro.com/afvb/general-chat/72182-piston-glazing-your-modern-diesel.html

haha - posted this before I saw your answer Pat :)

[rick130]

Look at the gap between bonnet and guards - no need for vents on there at all - especially on a diesel..

However, if you like the look that's your prerogative.


I've wool tuff tested a Defender and the air flows from outside to in at that point.

Pulled the blanking plate from the top of the guard, and again, the air is turbulent and reversion is happening, it's pretty messy.
The underbonnet area of the Defender is IMO really poor for air flow, indicated by the need for a functioning fan at speed !

In most cars the best spot for bonnet vents are just behind the radiator in a place of laminar flow.
The base of the windscreen is a no no, as its a high pressure area and pushes air back into the engine bay.
The best spot for a Deefer, especially with the windscreen vents is where Serg has his on the guards.
It works.

[Didge]

Hey TheStig, if the vents make you happy then that's all that matters. If people are worried about air flow and as Jeff above said, the "a" word (aerodynamics) then they've bought the wrong car and in a really big way. Anything you can do to bling up an older Defender can't be that bad (makes them look less tired, keeps us enthusiastic and that helps us keep the car on the road) - I've wondered about getting some of those late model Disco side vents on my old girl just to tart it up a bit

[AndyG]

I must confess, i have cast an eye over these ............

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[rick130]

Hey TheStig, if the vents make you happy then that's all that matters. If people are worried about air flow and as Jeff above said, the "a" word (aerodynamics) then they've bought the wrong car and in a really big way. Anything you can do to bling up an older Defender can't be that bad (makes them look less tired, keeps us enthusiastic and that helps us keep the car on the road) - I've wondered about getting some of those late model Disco side vents on my old girl just to tart it up a bit

Read the post above yours, it isn't about aero, it's about getting the hot air out of the engine bay.

The Defender engine bay is atrocious, air doesn't flow out fast enough and so becomes a high pressure region so air doesn't flow through the radiator well enough for optimal cooling.

No, I haven't taken pressure readings in the engine bay but I have enough anecdotal evidence (that I don't have time to go into ATM) to suggest this is the case.

[TheStig]

Firstly I would just like to thank everyone for their opinion and secondly I would just like to inform all of you who are concerned about the aerodynamics that I have not lost any fuel economy (so musnt have any effects on the aero) and they are actually prolonging the life of the engine because when you go 4x4ing u don't have a high air flow in the engine so all the heat is trapped, these vents let the hot air escape.