‘74 DS Resto

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If you had significant louvres, at standstill normal convective flow would be adequate.
I don't think there is any need to add fans, which add energy into the air, just let the hot air that is there, out.
Hmmm, but is there anywhere for convective airflow that isn't drawing past or through a significant source of heat? At standstill air is really only filtering up past a hot engine or getting drawn through a hot radiator. The DS has one of the most "sealed in" engine bays I've encountered in an older water cooled car. The amount of heat generated by one or two 90W thermo fan motors isn't much considering (depending on the DS model) it is sharing the engine compartment with a heat source generating up to 100,000W of energy. If this source of heat (the fan motor/s) is/are located at the very top of the engine bay on the underside of the bonnet, wouldn't that positioning therefore aid convection?
I believe one of Citroen's last mods to "improve" the cooling system of the DS was to add a supplementary electric radiator fan?

How about using the aluminium bonnet as a heat sink, strip the underside of padding/paint and give it a very thin coat of primerless flat black, weld fins lengthways down the bonnet on the topside and polish the whole upper surface so it doesn't absorb heat from the sun. Look the ducks guts on a silver car! I was going to say weld the fins on like chevrons, but I don't think these would flow as well as straiģht ones.😁

I had a slightly modified P6 Rover many, many years ago, these cars also suffer from a tightly packed engine bay. It was the later series with the "power bulges" pressed into the aluminium bonnet. As I already had the bonnet stripped I thought I would polish the bulges and mask them off before I painted it, just for something different. Interestingly when the car was hot, the polished parts of the bonnet were relatively cool to touch, whereas the adjacent black paint got bloody hot. The entire underside of the bonnet was painted satin black. You can see the polished bulges in the photo, either side of the "hood ornament".😉
Sorry about the quality, it is a digital photo of a old "real" photograph.
Rob.
 

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Ramaling

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Yes, the cendrier was an attempt to reduce hydraulic fluid temp....... by improving general air flow.
However, they then made two discoveries.
The radiator air was recirculating when the car was standing still, so cooling was greatly impaired.
And a large part of the hydraulic fluid heating was coming from the combined engine coolant pump/ hydraulic low pressure pump (used to regulate the gearshift speed)
The heat was transmitted from the coolant to the hydraulic fluid via the aluminum body housing the 2 pumps.

So...... with the second front cars, the radiator got an inlet duct to stop air recirculation.
And the speed regulation of the BVH was replaced by the centrifugal regulator system.

So the experiment of the cendrier was only used for one year of production.
I suggest it was probably a very good way to improve the general air circulation.

From many years of building and flying model aircraft, I learned that engine cowls need to be designed carefully so engine cooling was not reduced.
The rule of thumb, was that air exit area needed to be 2 x times the inlet area.
As the cool incoming air is heated it expands, and the exit space needs to be more. Also a continuously reducing pressure gradient is needed to maintain flow through. The exit must not restrict the flow.
In a Dee I believe there is plenty of inlet area, it's the exit that is lacking.
While it may have been found that a significant amount of the air moves forward again to exit, I'm sure this is not how it should be. The best flow through would be achieved with BIG vents in the rear parts of either the bonnet or wings.

Cendriers are the only genuine original factory accessory to achieve it.
I've "googled" the cendriers and have found them in the first iteration of the ID/DS front but not in the later versions with the closed in headlights. I agree they look good. "Cendrier" means ashtray and they all have parallel grills and strongly chromed surrounds. About 30 years ago I knew a guy out back in Queensland who retrofitted a DS23 fuel injected car with cendriers made of expanded mesh. Didn't quite have the same strong appearance as the originals.
 

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They only fitted those vents to the top of the wings for a couple of years, never on the 3rd front cars. I have a plan to cut out the bottom of the wings in this area as another path for air to leave the engine bay

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Ramaling

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Cendrier 1a.png
Cendrier 1a.png
Cendrier 2a.png
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I found these images of the cendriers. It seems there was a significant internal panel difference in the wings. They would work very well with the more open wing construction of the later cars. Maybe they could be constructed from scratch using highly polished stainless steel or maybe chromed mild steel
 

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They only fitted those vents to the top of the wings for a couple of years, never on the 3rd front cars. I have a plan to cut out the bottom of the wings in this area as another path for air to leave the engine bay

View attachment 133656
Not sure if that area will allow air out or not. I believe the area behind a rotating wheel enclosed in a wheel well is high pressure? Depending on the difference between the under bonnet pressure and wheel well pressure the air may flow either way or possibly stagnate?
There was an earlier post that showed external vents fitted in the the outer skins (roughly behind the area you have circled). These would be fed from the engine bay via the cavity in the guard behind the wheel tub. This is pretty much where the gills are on a HQ Monaro (although positioned a bit higher on the Monaro) I know these work as when the engine in my Monaro was getting really tired (with lots of blowby) the gills had long trails of oil vapour coming out of them leaving dirty black streaks down both sides of the car.
Rob.
 

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They only fitted those vents to the top of the wings for a couple of years, never on the 3rd front cars. I have a plan to cut out the bottom of the wings in this area as another path for air to leave the engine bay

View attachment 133656
That is where my DS23 had the additional holes. ... with I suspect minimal benefit. The hot air would be at the top not the bottom.
 

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Hmmm, but is there anywhere for convective airflow that isn't drawing past or through a significant source of heat? At standstill air is really only filtering up past a hot engine or getting drawn through a hot radiator.
Rob.
Uhhh?
That's what we want.... isn't it?
Convective flow works by introducing cool air, allowing it to flow past a heat source, expand, become less dense, rise and escape.
The convection flow is caused by the rising less dense air.
You want it to take heat from the hot bits in the engine bay.
The inlet vents should be low. The outlet vents should be high.
That's why you would not need fans.
 

Greenpeace

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Uhhh?
That's what we want.... isn't it?
Convective flow works by introducing cool air, allowing it to flow past a heat source, expand, become less dense, rise and escape.
The convection flow is caused by the rising less dense air.
You want it to take heat from the hot bits in the engine bay.
The inlet vents should be low. The outlet vents should be high.
That's why you would not need fans.
I realise how convection works, what I am saying is at standstill the air under the car is already contamintated by the radiant heat off the exhaust, engine sump etc so is unlikely to want to go upwards past the sides of the engine in a hurry unless the hot air above is being rapidly removed. Flow through the radiator again is only introducing heated air (80 - 90C) into the engine compartment. If I was to cut a hole somewhere leading into the engine compartment and stick a heat gun in it set at 90C would that aid convection? Surely introducing an untainted source of cool outside air low down in the engine compartment would chase hot air out better that these other two sources? Sans these hypothetical cool air vents I don't believe hot air is going to be fighting to get out of any bonnet louvres/vents while the car is standing still. Yes there would be flow, but would it be from convection or from the volume of air introduced via the engine fan?
Porsche and Lotus have both produced models with fan forced engine bay ventilation systems to reduce/prevent heat soak at stationary/low speeds. If they could have addressed their respective engine bay's excess heat problems with just additional vents or louvres to promote convection, I'm sure they would have.
If relying on stand alone convection was always the answer for heat dispersion, (modern) cars wouldn't need water pumps and radiator fans.
 

Ramaling

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I realise how convection works, what I am saying is at standstill the air under the car is already contamintated by the radiant heat off the exhaust, engine sump etc so is unlikely to want to go upwards past the sides of the engine in a hurry unless the hot air above is being rapidly removed. Flow through the radiator again is only introducing heated air (80 - 90C) into the engine compartment. If I was to cut a hole somewhere leading into the engine compartment and stick a heat gun in it set at 90C would that aid convection? Surely introducing an untainted source of cool outside air low down in the engine compartment would chase hot air out better that these other two sources? Sans these hypothetical cool air vents I don't believe hot air is going to be fighting to get out of any bonnet louvres/vents while the car is standing still. Yes there would be flow, but would it be from convection or from the volume of air introduced via the engine fan?
Porsche and Lotus have both produced models with fan forced engine bay ventilation systems to reduce/prevent heat soak at stationary/low speeds. If they could have addressed their respective engine bay's excess heat problems with just additional vents or louvres to promote convection, I'm sure they would have.
If relying on stand alone convection was always the answer for heat dispersion, (modern) cars wouldn't need water pumps and radiator fans.
Don't underestimate the massive benefit of thermo-syphoning compared to pumps. Modern nuclear power plants rely on it as their ultimate safety pathway for heat elimination in the event of power failure to the primary cooling pumps. Even nuclear powered submarines use it in stealth mode by turning off their cooling pumps, dramatically slowing the reactor and powering the sub on nuclear decay heat convected to the generators via thermo-syphoning.

I like the concept of the cendriers because they follow the KISS principle. Their addition would make the existing engine driven fan vastly more efficient and pull air up from the sides of the engine provided its hotter than the road region. If its not then they would enable the air to flow the other way again via thermo-syphoning. Either way, the car no longer suffers from a heat loss disadvantage compared to other vehicles.

Now for the angle grinder, fly wire and duct tape!
 

DoubleChevron

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View attachment 133657 View attachment 133657 View attachment 133658 View attachment 133659 View attachment 133660

I found these images of the cendriers. It seems there was a significant internal panel difference in the wings. They would work very well with the more open wing construction of the later cars. Maybe they could be constructed from scratch using highly polished stainless steel or maybe chromed mild steel

They probably work well in traffic .... but may possibly comprise the cooling at speed (if its a high pressure spot, they'll be fighting the radiator pushing air into the engine compartment....... If you could close them when the car is moving at speed automatically ................. :)
 

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Don't underestimate the massive benefit of thermo-syphoning compared to pumps. Modern nuclear power plants rely on it as their ultimate safety pathway for heat elimination in the event of power failure to the primary cooling pumps. Even nuclear powered submarines use it in stealth mode by turning off their cooling pumps, dramatically slowing the reactor and powering the sub on nuclear decay heat convected to the generators via thermo-syphoning.

I like the concept of the cendriers because they follow the KISS principle. Their addition would make the existing engine driven fan vastly more efficient and pull air up from the sides of the engine provided its hotter than the road region. If its not then they would enable the air to flow the other way again via thermo-syphoning. Either way, the car no longer suffers from a heat loss disadvantage compared to other vehicles.

Now for the angle grinder, fly wire and duct tape!
Horses for courses, as you stated rely on thermosiphoning for "emergency cooling". The systems that assist basic thermosiphoning to provide consistent reliable cooling to a nuclear reactor are quite complex.
Nuclear submarines that rely on pumps for "long term" reactor cooling generally have a backup pump system (for the core) in case the main pumps fail.
A modern car engine will do the same (thermosiphon) with the water pump and fans disconnected, but for how long?
I believe at one point during the 7 Mile Island incident the plant engineers thought "natural water movement" would provide cooling to the core, the rest is history.
 

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I realise how convection works, what I am saying is at standstill the air under the car is already contamintated by the radiant heat off the exhaust, engine sump etc so is unlikely to want to go upwards past the sides of the engine in a hurry unless the hot air above is being rapidly removed. Flow through the radiator again is only introducing heated air (80 - 90C) into the engine compartment. If I was to cut a hole somewhere leading into the engine compartment and stick a heat gun in it set at 90C would that aid convection? Surely introducing an untainted source of cool outside air low down in the engine compartment would chase hot air out better that these other two sources? Sans these hypothetical cool air vents I don't believe hot air is going to be fighting to get out of any bonnet louvres/vents while the car is standing still. Yes there would be flow, but would it be from convection or from the volume of air introduced via the engine fan?
You've answered it yourself....

Drawing air through the radiator (by fan) is cooling the engine.

Allowing that air to then escape outside the car carries that energy away.

If you add to that a general air flow through the engine bay, introduced by the forward movement of the car, while driving, or by convection, while at standstill...... the excess energy is removed.
The issue is not finding a source of relatively cool air, the issue is allowing the heated air to escape.

Your analogy of putting a 90 degree heater at the inlet is in no way comparable with the system.
You are describing the introduction of more energy from outside.
Heating of the air from the radiator or from contact with the surface of the engine/ gearbox/ exhaust, and then having it flow out through vents is removing energy from the system..... the complete opposite!
 

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We are now discussing three different subjects, one is heat transfer, one is air pressure, the other is convection. The heat removed from the engine via the radiator is blown straiģht back into the engine compartment by the fan and/or incoming air pressure, so unless I'm mistaken the energy hasn't really gone anywhere. We may as well run the exhaust pipe back in there too.
Of course the addition of vents will allow hot air to escape, but there's no other kind of air in the DS engine bay anyway. But what percentage would be from convection alone? I believe the displacement from incoming air would be the greatest contributor to any flow out of these hypothetical vents, any effects from convection would be merely ancillary.
 

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When I took Buttercup to Paris for the Jubilee, on the Sunday was a parade of 2,000 Dees through the streets from the triumphant arch to the tower of Eiffel, via here and there. The organisers had grossly underestimated the time and road space needed by such a convoy, and about 2/3 of the way through it became a giant traffic jam, but with party atmosphere. The most surreal day of my life.
Many many Dees had to lift their bonnets whenever stopped, BUT it was only the 3rd front cars.
I didn't see any with single headlights with the bonnet up.
 

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Ancillary, but enough!
We just need someone with a standard car and some carefully positioned thermal probes (and perhaps a differential pressure manometer) to collect some data, start chopping and repeat the checks. This will need to be conducted in a controlled environment to ensure the results are not tainted in any way.
I'm busy, any takers.😉
 

Buttercup

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I just reread your latest post.
Is your idea of convection, just air trying to circulate only within the engine bay confines?
My idea of convection is cool air coming in from under the car or through the front apertures, then being heated by the various sources within the engine bay, then exitting through a high up aperture.
Obviously late cars with rear edge bonnet seals don't have an exit aperture high up.
So........ I'm suggesting we provide one.

At no time did I suggest that a convective flow within the closed space was going to contribute much.
 

Greenpeace

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When I took Buttercup to Paris for the Jubilee, on the Sunday was a parade of 2,000 Dees through the streets from the triumphant arch to the tower of Eiffel, via here and there. The organisers had grossly underestimated the time and road space needed by such a convoy, and about 2/3 of the way through it became a giant traffic jam, but with party atmosphere. The most surreal day of my life.
Many many Dees had to lift their bonnets whenever stopped, BUT it was only the 3rd front cars.
I didn't see any with single headlights with the bonnet up.
More HP.😉
I just reread your latest post.
Is your idea of convection, just air trying to circulate only within the engine bay confines?
My idea of convection is cool air coming in from under the car or through the front apertures, then being heated by the various sources within the engine bay, then exitting through a high up aperture.
Obviously late cars with rear edge bonnet seals don't have an exit aperture high up.
So........ I'm suggesting we provide one.

At no time did I suggest that a convective flow within the closed space was going to contribute much.
 

Buttercup

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We just need someone with a standard car and some carefully positioned thermal probes (and perhaps a differential pressure manometer) to collect some data, start chopping and repeat the checks. This will need to be conducted in a controlled environment to ensure the results are not tainted in any way.
I'm busy, any takers.😉
And.... just what is a standard car?
 

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No I am familiar with hot air rising. But if the pressure existing in the engine bay exceeds the ability of heated air to rise up past the sides of the engine "It ain't happening". Hence I suggested sourcing cooler air from somewhere further forward. As to the bonnet seal who knows, traditionally this area at the base of the windscreen was utilised to force air in. Scuttle venting, reverse bonnet scoops, cowel induction etc. Open the under dash vent in an old Valiant at 60mph (these are connected directly to the plenum at the base of the windscreen) and you'll soon be rid of any loose paper laying round on the floor. Perhaps when idling in Paris the seal's presence may be a hindrance but I think at speed the air flow in this area would actually be trying to push in. Whether it can or not would depend on the pressure present in the engine bay.
And.... just what is a standard car?
One that doesn't have holes cut in it already????
 
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