descaling DS cooling system
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  1. #1
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    Default descaling DS cooling system

    Having spent considerable time and $ over the past few months trying to get my 1974 DS23 (carby, BW auto) into shape such that it could be driven in moderately warm weather, I find, having just had the radiator recored that it still doesn't like trips to the Adelaide Hills, or cruising at much more than 50 mph - other than down hill - even when it's only 20 deg C. Cruising around town at 35 mph it's fine, but under more arduous conditions, the temperature keeps climbing to 212 deg F - or more - on my Smiths mechanical temp / oil pressure gauge; likewise, into the lower red section of the instrument panel gauge (new sender recently fitted). (I have checked the mechanical gauge with another thermometer and they're within a couple of degrees of each other.)

    Prior to having the radiator recored, I fitted a Baldwin coolant filter in the heater radiator circuit. Although it's a bypass setup, it didn't take many miles to clog the filter (hot hose on the filter inlet side, cool on the outlet).

    In researching Baldwin's coolant filters, I discovered information about descaling wet sleeve truck engines to keep their cooling systems in good order, but I'm not sure how applicable the techniques (and products) would be for a D motor. I emailed Baldwin's "Help" centre in the US a couple of times, but got no reply.

    Of course, all of this assumes that a D motor which has been run for many years with "proper" coolant might have scale build-up, which could cause cooling system issues. Does anyone have a view on this?

    Before responding, I draw readers' attention to the attached photo of the two sides of my old radiator core ("shiny" side of core - inlet from engine; "cruddy" side - outlet to water pump).

    The radiator specialist who did my recore has apparently done quite a few Ds and rather than the typical "why don't you just get rid of it [the car] mate" he went into the whys and wherefores of the cores he uses for the cross-flow Ds, which apparently come from Western Australia. They are 28 x 3 row, but of larger tube section than the original (43 x 3 row - see photo) and have more air space, which he claims gives better cooling efficiency, due to better air flow through the fins.

    The car is definitely running cooler with the new radiator, but I wouldn't risk a drive to the Adelaide Hills today (forecast max, 30 deg C) let alone on a 40 deg day.

    By the way, I've checked the following: water pump - excellent condition; (123 ignition) timing - slightly retarded from 'pinging under load' (BW trans Ds don't have the convenient static timing mark of the manuals); carby well tuned; correct (new) spark plugs; 16" high performance Davies, Craig electric fan in place of mechanical fan (switches on at 88 deg C); Davies Craig Electric Water Pump (switches on at 85 deg C; boosts coolant flow via separate circuit, as follows: suction, T'd from water pump suction (near radiator lower outlet) - through non-return valve - to EWP - delivery to base of housing between water pump and head); no thermostat.

    Steve (California) provided some useful tips on cooling Ds some months ago - which I've largely followed - but he DID NOT recommend doing away with the thermostat. I'd like to understand why (apart from the fact that having no thermostat does extend the warming up time). Even when fully open, the thermostat creates a significant restriction to coolant flow and I don't understand how keeping the coolant in the engine helps heat transfer (and thereby assists cooling) in hot weather.

    I would also like to better understand the theory behind the operation of the 'shark's mouth' air intake of the D. It strikes me as a most inefficient way to get air into a radiator. Also, on my car, the lower part of the front number plate extends nearly 2" below its mounting panel, which would also seem to deflect air away from the radiator air intake.

    There are a lot of variables in play here and I apologise for creating such a complex scenario for discussion. Although this topic has been tackled before, have the key ingredients for keeping a D cool actually been identified? Do we have THE SOLUTION?

    Chris

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  2. #2
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    May i suggest that yoy place a stocking in the hose from radiator to pump and change frequently until that rubbish disappears, Check that your thermostat does in fact fully open and that your electric fan is working,Andy.

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    Is the electric fan actually coming on?

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    1000+ Posts daffyduck's Avatar
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    Is the water pump belt slipping?

  5. #5
    Real cars have hydraulics DoubleChevron's Avatar
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    Dumb suggestion, but the fan isn't hooked up backwards is it ?? ie: it gets warm and the fan switches on .............. backwards clobbering all airflow through the radiator.

    seeya,
    Shane L.
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    When I first got my car D Special with 23 motor and crossflow radiator, it used to overheat in traffic.

    Without changing anything other than replacing the vinyl chute for a re-manufactured one my problem was cured and remains so, IMO the system works without any modifications.

    Make sure the vinyl chute has no rips or tears, I think it is one of the critical components in the cooling of a D, it has as much to do with it's ram effect when the car is in motion as it's ability to make full use of the fans(s) when the car is stationary.

    My

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    Fellow Frogger! mberry's Avatar
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    Your car should be able to tear through the Adelaide hills on a 30º day without problem.

    1. Is the fan turning in the right direction, pretty easy to have swaped the wires over?
    A friend had a fully rebuilt DS auto here in Melbourne last summer by the premier DS Citroen workshop...... car kept overheating in traffic, fan was spinning in wrong direction.

    2. Did you replace the bottom radiator hose when you recored the radiator, did you get the steel spring re-enforced hose?

    I have heard the WA theory on more air flow, I understand they get hot over there and they say they have been successful. But, there is another theory about airflow to surface area ratio. the solution contradicts this.
    Having more water flow through the radiator faster, does not make sense to me, if you're trying to cool the water down. Surely you would want slower flow with more exposure to cooling air flow, so the water can get a chance to cool down before returning to the engine?

    P.S. I swear by the stocking in the top radiator hose.

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    Have you replaced the thermostat it can cause many problem even opening very slow getting rid of the scale from the motor is a slow job I have worked with radiators for some time High pressure flush of the motor will help but it may need to be done many times to get rid of it
    I hope this help you out

  9. #9
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    If you do not have a thermostat or it is not closing properly you will get carby freezing like I did recently. If you do have one and it does not open you will of course get overheating.

    Is the electric fan in front or behind the radiator. IIRC others have found better success with the fan behind pulling cool air through rather than trying to push it through. I think a vacuum cools air?

    I have driven my D Special in hot Adelaide weather and traffic and it only just got above 90c on the added gauge and that was while sitting or crawling in traffic.

    Having a fan come on when the engine is already considerably warm could be a challenge to the system as it is behind the 8 ball to begin with. Surely a lower turn on temp would help keep the cool better than trying to play catch up.

    I also agree with the stocking in the top pipe idea and have used it before. I would be reluctant to put something into an otherwise functioning engine that may just be enough to push the engine over the edge as crud starts to loosed and move around. If you were planning to do a full rebuild then of course it may assist.
    Craig K
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    Chris

    Just make sure the vinys shute is properly screwed onto the radiator, 2 screws fell out on my ds and sufficient ventilation didn't pass through the radiator and my engine ran considerably warmer, just something to check again.

    The stocking is the best idea, it is unbelieveable how quickly a new core can get clogged with old crap, you said that the special filter you had got blocked quickly, so, just put in that stocking on the top hose

    Goodluck!!
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  11. #11
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    Default descaling DS cooling system

    Thanks everyone for your prompt replies.


    I respond as follows:
    • Several people don't recommend descaling - and I gather no-one (to date) is in favour.
    • The stocking seems to be in favour as a rubbish filter.
    • Electric fan: it's a 14" DC, not 16" - only just fits on the inside of the radiator and
      • yes it is turning the right way (sucks cloth onto the front of the radiator with great gusto - e.g. if the shroud is removed); and
      • yes it is turning on (it's a lot quieter than the mechanical fan, but you can hear it cycling - and see the temp gauge move in concert with the fan noise - especially with the driver's window down).
    • Vinyl radiator chute - mine is in good condition (not perfect) and is well attached to the radiator surround.
    • Water pump belt(s) slipping - I've got them reasonably tight (can't turn the water pump by hand and I can't hear any belt squeal).
    • Bottom radiator hose - mine has the curved steel pipe joining two short hoses - one at the radiator end and one at the water pump end and neither has a steel spring insert to stop hose collapse. I don't think there's sufficient hose length for that to occur.
    • Thermostat - I currently don't have one installed, but mine is OK (recently tested on the stove). See further below.
    • Electric fan 2 - see below.
    In addition to your responses to this thread, this afternoon I've had an interesting an enjoyable discussion about this case with Richo.

    He is adamant I should not be running the engine without a thermostat and I don't disagree with his logic. There are two reasons why I don't have a thermostat fitted at the moment (while I try to sort this out). The first is that my first trial was with the Davies Craig 14" electric fan and the EWP, which comes in a kit with an electronic controller which has three EWP trigger temperatures: 75, 85 and 95 deg C. They suggest you select the one nearest the thermostat opening temp, hence my choice of 85 deg. The electric fan then cuts in 3 deg above the EWP. The EWP cycles every 30 sec or so when the engine is cool, thereby theoretically avoiding hot spots and speeding warm-up. Given this arrangement, they recommend not fitting a thermostat (as long as you have the full electronic control unit). During this trial I disconnected the mechanical water pump.

    When I found the coolant was still getting hot, I re-plumbed the system with both the EWP and the factory water pump (without mechanical fan) and still left the thermostat out - all in the interests of maximum flow for a short trial period (50 miles max). I found that re-activating the factory water pump improved cooling, but was still unsatisfactory.

    Richo pointed out that the mechanical fan not only draws air through the radiator to help cool the coolant, but it also causes a continuous gale to blow through the engine bay, thereby removing the hot air built up around the engine. With the electric fan only coming on once the coolant reaches 88 deg C, there would be minimal airflow when the fan isn't running, which would exacerbate the heat build-up (which, I think, is also UFO's point).

    Being an auto, my car has an ATF cooler which used to be fitted in front of the radiator. I've moved it to the front left valance where one air conditioning condenser used to be and I've made up a frame which also supports the original factory auxiliary electric fan and is switched by an adjustable Davies Craig thermo switch whose sensor is mounted in the top radiator hose (yes, where the stocking would go!).

    As a trial I could try swapping the two electric fan switching devices and thereby set the main fan to come on at a very low temp (I think the minimum setting is 40 deg C coolant temperature). In that way, I could run the main cooling fan continuosly from when the engine is relatively cool.

    If that works, it may be a case of removing the Davies Craig fan and replacing the orginal mechanical fan - or even reverting to the original set-up completely!

    And a lot of people will say why did you frig around with it in the first place!!

    By the way, Richo also mentioned the possibility of an air lock in the coolant, but I don't think that's an issue. He suggested that I get hold of a pyrometer and check for hot spots - a good idea.

    Thanks again for all your responses.

    Chris

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    1000+ Posts daffyduck's Avatar
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    It has been mentioned to me, that some of those replacement radiator cores are not up to the task, regardless of what the guy at the shop says. Something about the placement/array of the core tubes and fins.

    Any chance you could have a look see at a buddy's car that isn't running hot and do a visual comparison?

    I have one car that comes around that runs cool as a cucumber, even on 105f days, even with the A/C on.. I think that one has a very dense 4 row core in it.

  13. #13
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    Default 3 v 4 row radiator cores

    Daffyduck,

    There seem to be some divergent opinions about 3 row versus 4 row. I recently spoke to someone with a 4 row core who said they felt it was only marginally, if any better than a decent 3 row core. I think others on this Forum have also reported "cool running" with 3 row cores - but I suspect there are 3 row cores and 3 row cores.

    What's a "decent 3 row core" - or 4 row for that matter? My new core has 28 x 3 rows, whereas the old one (see photo above) has 43 x 3 rows. The radiator specialist who fitted my new core said that the virtues of the new core are that the tubes, being of larger cross-section, are less likely to blockage and because of the wider spacing between the tubes - and the structure of the fins - there is better airflow and therefore, better heat exchange.

    I understood from our discussion before he did the job that he had access to two makes / construction of core suitable for the D, but the one fitted was considered superior.

    I based my choice of repairer on recommendation and his deemed experience with the D. Of course he is unlikely to divulge whether his recommendation is based on other factors, such as his credit rating with suppliers, other terms of trade, such as margin, etc. At the end of the day, there's a reasonable element of good faith involved in the transaction.

    Chris

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    Default lost post

    Last night I thought I spotted a posting on this thread by Jo. As I recall he queried how I had set up the Electric Water Pump in relation to the original belt driven pump.

    I started to draft a response and decided that a picture was worth a thousand words, so I then created the attachment to this posting. In between, I had to use the Internet for something else and when I came back I couldn't find Jo's posting or my part-written response. And I still can't find it. I hope I haven't parked it in cyberspace somewhere! If so, I apologise.

    As to the set-up, hopefully the attachment explains it reasonably well. Bear in mind that there's a 14" Davies Craig Hi Performance electric fan bolted to the engine side of the radiator and there is no mechanical fan on the water pump.

    The EWP suction runs parallel to the radiator above the steering rack and the EWP is mounted on its side (to avoid air locks) just left of the high pressure hydraulic pump and between it and the electric fan. The EWP delivery line (radiator hose) runs between the upper and lower runs of the hydraulic pump belt drive in a sweeping 90 degree arc up to the underside of the water pump manifold, into which I've tapped a 1" brass pipe fitting (in the flattish area on the underside of the housing, near the temp gauge sender point).

    I hope this makes it clearer. I could attempt to take some photos if anyone is interested.

    Chris
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    From reading what you posted, is it possible that the water is circulating too fast?

    The thermostat places a constant restriction on the coolant flow, but that restriction is designed into the rest of the system.

    I noticed you said that when the mechanical pump was reconnected, that the cooling improved a little. Is it possible that it was adding a resistance of some sort, effectively slowing down the water supply of the EWP?

    The hot water needs to spend some time flowing through the radiator for it to transfer it's temperature to the ambient air.

    With the bigger freer flowing core openings and the EWP combined with no thermostat, the water may be passing through the radiator so fast that it doesn't have the chance to dump it's heat.

    You could check the temperature differential on both sides of the radiator.

    Also, is there any chance that the water pump housing has corroded internally, allowing some of the water to bypass the engine?

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    P.S - The way that air is flowed into the radiator on a DS is actually the most aerodynamically efficient way to do so and is similar to many WW2 planes such as the Mustang.

    The air opening should generally be 1/4-1/3 the size of the radiator and mounted in a high pressure spot (ie the front of the car) The radiator should be some distance back from the intake to reduce the ability of the air to spill back out of the opening.

    Below is a picture of a P51 mustang, a design so efficient that it was supposedly 'zero loss' in some cases (ie the thrust created from the hot air exiting the system was equal to the drag induced).

    It should be noted that without air flow, the system would struggle more than a radiator just hanging out the front...


  17. #17
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Citquery View Post
    Last night I thought I spotted a posting on this thread by Jo. As I recall he queried how I had set up the Electric Water Pump in relation to the original belt driven pump.

    I started to draft a response and decided that a picture was worth a thousand words, so I then created the attachment to this posting. In between, I had to use the Internet for something else and when I came back I couldn't find Jo's posting or my part-written response. And I still can't find it. I hope I haven't parked it in cyberspace somewhere! If so, I apologise.

    As to the set-up, hopefully the attachment explains it reasonably well. Bear in mind that there's a 14" Davies Craig Hi Performance electric fan bolted to the engine side of the radiator and there is no mechanical fan on the water pump.

    The EWP suction runs parallel to the radiator above the steering rack and the EWP is mounted on its side (to avoid air locks) just left of the high pressure hydraulic pump and between it and the electric fan. The EWP delivery line (radiator hose) runs between the upper and lower runs of the hydraulic pump belt drive in a sweeping 90 degree arc up to the underside of the water pump manifold, into which I've tapped a 1" brass pipe fitting (in the flattish area on the underside of the housing, near the temp gauge sender point).

    I hope this makes it clearer. I could attempt to take some photos if anyone is interested.

    Chris
    Sorry, deleted post as I got the impression I was being ignored, and thought, why bother..
    I must have been a bit oversensitive yesterday.
    Thanks for the reply, back on the case with a new layer of thick skin.
    Jo
    Last edited by jo proffi; 7th December 2011 at 12:28 PM.

  18. #18
    Real cars have hydraulics DoubleChevron's Avatar
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    Hang on ..... Have you removed the engine driven fan ?? I have never heard of anyone being successful in doing this. It moves far more air than any electric fan can. By electric fan I was thinking the one that works at the same time as the engine driven fan.

    If you have removed the engine driven fan ........ You need to put it back!

    seeya,
    Shane L.
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  19. #19
    1000+ Posts jo proffi's Avatar
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    I'm still slightly confused about if you are aiming to run it with or without the mechanical water pump.
    If you run this system without the mechanical water pump connected, what stops the coolant flowing back through the water pump the wrong way and completely bypassing the engine and radiator??


    Jo

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    Default DS23 with Davies Craig EWP and electric fan

    Thanks for your further responses.

    I reply as follows:

    mistareno - re "over-pumping", I quote from Davies Craig website (EWP FAQs)


    Is the idea that coolant can pass too quickly through a radiator true?

    The "pump too fast lose less heat” notion is very popular and many experienced mechanics are very attached to it but – it is a fallacy. Davies Craig has been carrying out research and development for over a decade on a number of projects and has never been able to pump genuine liquid coolant faster and lose less heat. In all car engines, when the mechanical pump reaches cavitation speed, coolant turns into a gaseous state which is compressible,(liquid is not) and the real flow rate of liquid coolant drops even though the mechanical pump has a higher rpm, and so heat loss drops. The engine temp then rises. And it only seems like the flow rate is too fast, and the coolant is spending too little time in the radiator to lose its heat etc. etc..





    re the water pump housing possibly being corroded - it's all new, so no leakage directly to the thermostat chamber. What's going on inside the cylinder head and block? I don't know, but it has been running good quality coolant for the 15 years I've owned it.



    mistareno - re aerodynamics; Richo also explained the aerodynamics of the air movement from in front of the car, under the valance and into the radiator intake / radiator and through the engine bay. Whilst I sort of got it, I wonder if anyone can point to a good written and diagrammatic explanation of the specific Citroen D series scenario. I appreciate that it's important. It would be useful to completely understand the theory and practice.



    Shane - yes, message understood! Again, it would be nice to have a quantitative comparison of air flow via the factory set-up v the elctric fan (whose performance is readily accessible on the Davies Craig website).



    Jo - I've trialled both with the two pumps in series (i.e. EWP in the suction line to the mechanical pump); EWP on its own (dedicated large bore suction from radiator direct to EWP, mechanical pump suction blocked off and belts off - the 800mm? hydraulic pump belts also drive the alternator direct from the cam-pulley, by-passing the mechanical water pump); and the EWP and mechanical water pump in tandem (parallel) as shown in the diagram above.



    In the last case, the mechanical pump is pumping the whole time, so it "stops" the EWP pressurised coolant flowing back to the radiator and bypassing the engine and when the EWP isn't running, the non-return valve stops coolant pressurised by the mechanical pump from returning direct to the lower radiator outlet.



    Re earlier queries about not runnuing a thermostat - again, I quote from the Davies Craig website (EWP FAQs), noting, (minor detail) that the available temperature settings are now 75-95:



    What do I do with the engine’s existing thermostat?

    If you choose to use the Davies Craig Digital Controller you should remove the engine’s thermostat – the Controller is the new “thermostat”. The Digital Controller allows you to electronically set the engine target temperature and it adjusts the rate of coolant flow, hunting for, and then locking onto the temperature you set. You have five (5) options; 70c, 75c, 80c, 85c and 90c for either economy or performance, unlike your thermostat, which is set at one temperature by the engine manufacturer.



    I think the key to all this might be Citroen's mechanical fan - and maybe there's some doubt about the actual cooling ability of the radiator core newly fitted.



    Thanks again, everyone.



    Chris

  21. #21
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    Chris,
    Thanks for an excellent thread and your methodical work though, still a way to go but interesting reading.

    This is a similar thread by member Pottsy
    DS Cooling

    ...and a reply by Brett R,
    DS Cooling

    On page 32 Reynolds discusses the redesign of the original DS front end which was introduced in September 1962 (not, I stress, the later twin light front). Reynolds says:

    'A plasticised fabric tube linking the duct to the main air intake to the radiator completely enclosed the airflow, so that ram effect was eliminated; air flow through the radiator now depended entirely on the action of the fan.'

    Also page 83 of the above mentioned text features an underbonnet photograph of a 1969 ID19B (with the last nose, of course). The caption to the photograph reads:

    'With the spare wheel removed, the ducting to the radiator can be clearly seen. Note the zip in the fabric shroud which is normally kept closed to maintain fan suction, normal ram effect from the nose being virtually nil. The battery has changed sides'


    Both the thread and the 'bold' comments from Reynolds may give you some assistance? (I made the comments bold).

    BTW, if you read Pottsy's thread through you will see that he gave up on modifications and returned to original for his best result.

    Cheers
    Chris
    74 D(very Special) >>Rejuvenation Thread<<
    08 C5 X7 HDi very Noir



    "Déesse" Roland Barthes, 'Mythologies', 1957

    The Déesse has all the characteristics of one of those objects fallen from another universe that fed the mania for novelty in the eighteenth century and a similar mania expressed by modern science fiction: the Déesse is first and foremost the new Nautilus.

    (Umberto Eco [Ed], The History of Beauty, Rizzoli, NY, 2004)

  22. #22
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Citquery View Post
    I think the key to all this might be Citroen's mechanical fan - and maybe there's some doubt about the actual cooling ability of the radiator core newly fitted.



    Thanks again, everyone.



    Chris
    Sounds logical

    Oh, and put your thermostat back in.

    just to add a little more info, your mechanical pumps a decent volume at a decent pressure.
    I dont know the exact specs, but I'll suggest 20psi would not be unrealistic at high revs.
    The thermostat restrictions helps the head achieve this type of pressure, which stops localised hotspots from boiling the coolant.
    The CD ewp in contrast is a high flow low pressure pump.According to their website graph, at around 8psi of back pressure, it stops flowing.
    This is not a subtle detail and is probably one of the reasons they dont want an obstructions like a thermostat in line.
    You'd want to make damn sure any system driven by the EWP had flow, because it wont have (pump produced) pressure, that is a given.
    I'd be removing it from the system, and going back to OE which obviously works on other peoples cars.

    I think you have nailed it with airflow being your problem.

    Jo

  23. #23
    1000+ Posts michaelr's Avatar
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    Quote Originally Posted by GreenBlood View Post
    Chris,
    Thanks for an excellent thread and your methodical work though, still a way to go but interesting reading.

    On page 32 Reynolds discusses the redesign of the original DS front end which was introduced in September 1962 (not, I stress, the later twin light front). Reynolds says:

    'A plasticised fabric tube linking the duct to the main air intake to the radiator completely enclosed the airflow, so that ram effect was eliminated; air flow through the radiator now depended entirely on the action of the fan.'

    Also page 83 of the above mentioned text features an underbonnet photograph of a 1969 ID19B (with the last nose, of course). The caption to the photograph reads:

    'With the spare wheel removed, the ducting to the radiator can be clearly seen. Note the zip in the fabric shroud which is normally kept closed to maintain fan suction, normal ram effect from the nose being virtually nil. The battery has changed sides'


    Cheers
    Chris
    My DS23 has both engine driven fan and the standard Citroen auxiliary electric fan. As I have fitted an electronic digital temp gauge I can see that the ram air effect does in fact produce a significant change to engine temperature even at quite low traffic speed.

    I would suggest that the ducted system was quite well designed as it takes air from a high pressure zone under the nose of the car.
    Michael
    Member, Citroen Car Club NSW

    DS23 Pallas 5 sp. "Francoise" , BX19TRi Auto "Jacques Dutronc" , Teardrop Trailer "The Toad", BMW R65 "Rosamund"
    In the past: Renault 750, Dauphine, R4, R8, R10, Peugeot 504 Familiale, ID 19 (x2), Safari (x2)

  24. #24
    Tadpole
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    Hi Michael,

    I also have a DS23 (auto efi) with factory standard cooling system and it copes with the hotest of days quite adequately.

    Same as you I have fitted a digital temp gauge for peace of mind and also notice that engine temp drops as speed picks up.

    I actually put this down to the increased efficiency of the engine driven fan as engine revs increase.

    With sustained idling on hot (38C+) days the engine temp will slowly creep up to 100C at which time the auxillary electric fan cuts in and pulls the temp back down to 85C or so. quite quickly.

    High speed driving and hill climbing even on the hottest of days see a stable temp of around 85C.

    In summary it appears that the faster the engine driven fan rotates the better the cooling ,looks like it is all based on suck rather than ram.

    Cheers,

    Mal

  25. #25
    1000+ Posts michaelr's Avatar
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    Quote Originally Posted by mcook View Post
    Hi Michael,

    I also have a DS23 (auto efi) with factory standard cooling system and it copes with the hotest of days quite adequately......

    In summary it appears that the faster the engine driven fan rotates the better the cooling ,looks like it is all based on suck rather than ram.

    Cheers,
    Mal
    I am still inclined to believe that the ram effect is a substantial contribution to the cooling. Sydney traffic is a great test location! Like you I have seen the temperature escalate to near 100 whist stopped on hot days in heavy traffic. When my electric fan was not functional I would raise the idle speed (By use of the pedal) to around 1500rpm with little effect. However, once the car was rolling again, even at low speed and often at less than 1500rpm, I could see a distinct temp drop.

    One day I will get a remote reading barometer (from a cheap weather station) and check the relative air pressures at play. I am particularly interested in finding a low pressure zone for exhausting hot air from the engine compartment. Australian dealers used to make vents in the lower part of the front guards behind the wheel. Maybe they would have done better venting from the lower rear section of the guard on that horizontal surface underneath or into the wheel arch?
    Michael
    Member, Citroen Car Club NSW

    DS23 Pallas 5 sp. "Francoise" , BX19TRi Auto "Jacques Dutronc" , Teardrop Trailer "The Toad", BMW R65 "Rosamund"
    In the past: Renault 750, Dauphine, R4, R8, R10, Peugeot 504 Familiale, ID 19 (x2), Safari (x2)

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