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  • To be honest a few people have had a crack at this without success. But I have never seen ALL the principles that have been discussed implemented.
    I appreciate its down to the packaging and amount of space available. Certaintly some principles are more important than others.
    Lets take shrouding. I have just looked at one manufacturers web site that suggests the difference in effectiveness between a unshrouded and shrouded fan is in the order of 40%. Then there is the fan itself that you are using. Again I expect you chose that one as it has a slim profile rather than maximum airflow. Unfortunate fact of life that the more powerfull the fan, the more current draw, the bigger the motor. Then there is the blades where the straight ones are more effective. So there might be some scope for improvement there.
    Both of these isues are of course dependant on the core depth taking up the available space. So the question is which of these is more important in terms of regulating the temperature where surface area and airflow seem to be the priority.
    Spal do a nice twin 280mm dual fan with integral shroud which is close to the 600X400 core size. In fact its almost the same dimensions as the V6 rad. Not cheap. I guess thats why I liked the idea of using that V6 dual fan shroud which could be modified to take either slimmer fans asuming the OE ones did not fit and were not up do the job. Of course without any dimensions its difficult to see how much space they take up. So I guess we have about 110mm (55mm for the rad core + 50mm for the fan). The shroud itself might not be very deep but clearly the compromise is the rad core depth. Is there a reason why the thread for the viscous fan couldn't be removed to gain same space?
    Another solution although its not very bling is to duplicate the OE arrangement with a viscous fan and a seperate shrouded electric fan. Thats what the S6 plus used. Seem to recall the S6 C4 used a bigger viscous than say the TDi models. Both have seperate shrouds. Thats assuming the thread on the boss is the same.The supplementary electric fan is mounted on its own shroud. Again it may mean replacing the OE fan with a slimmer one more powerful one. The dimensions of depth are within a few mm so should be to hard to adapt. Indeed it migh be possible to use two of those shrouds to cover most of the radiator surface area assuming you would be going to a larger rad, close to OE sized core
    Its sort of counter intuitive as to why the OE rad is not adequate when it seems to have close to the core size required. Perhaps people are using old clogged up ones or not incorporating all of the principles we have covered. As Alex as mentioned they may be improvements to have in core effeciency.
    Guess you will have do do your own research and satisfy yourself in terms of cooling what are the most important considerations, including other issues outside of the cooling system such as oil temperature for example. If the issue is primarily airflow through the rad then its prudent to look at how to improve that. Basically whats we have been suggesting.

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    • It must be quite close looking at this pic. Unfortunately no details just a random pic, but it does I think show a twin shrouded fan set up, possibily OE. Clearly the rad has been cocked somewhat, presumably to avoid that threaded section of the fan pulley. It the standard bumper not the V6 one.
      Attached Files

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      • Originally posted by twoqu View Post
        It must be quite close looking at this pic. Unfortunately no details just a random pic, but it does I think show a twin shrouded fan set up, possibily OE. Clearly the rad has been cocked somewhat, presumably to avoid that threaded section of the fan pulley. It the standard bumper not the V6 one.
        Going from that pic I would guess they have gone for an electric PS pump and deleted the A/C comp and Hyd pump to free up space especially on the RHS, leaving a simplified aux belt route like this,



        I think my next plan of attack will be to strip the radiator etc out then make a mock set up out of card board, wood etc, I still have my V6 shroud in the garage so can use that to help.
        Admittedly I under estimated the value of having a shroud on the rear and sealing the areas all round the radiator. I've looked at a few of the places that Alex suggested, they list all the various sizes of cores available so I can hopefully find one with efficient thickness and area yet still allow the fitment of a shroud.

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        • This sort of made me laugh although instructive as well!
          https://www.cgj.com/2013/09/06/why-y...the-right-one/

          Certaintly a large single fan might work although the start up current on some of the larger fans and indeed duals is starting to get problematic. I appreciate its pot luck where the motor might sit. The principle of shrouding still applies. The OE fan on the A8 looks like it was from a paddle steamer rather than the slimmer version on say the C4.

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          • That looks spacious compared to our S4
            Can you not reverse one of the hoses to use a conventional single pass rad?
            As I said earlier in the thread, I would fill the frontal area with a thinner, high quality core. A thinner core will generate you a bit more space for a good shroud & fans.
            Seriously though, Take a look at the B6 S4 shround below, it is very well packaged. If the rad will fit this would be a good bet.

            s-l1600 (1).jpgs-l1600 (2).jpgs-l1600 (5).jpgs-l1600.jpgs-l1600 (3).jpgs-l1600 (4).jpg







            Attached Files
            Panthero Coupé quattro 20vt
            Indigo ABY coupé
            Imola B6 S4 Avant

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            • Just been looking at viscous fans again. They do seem to be very effective in moving air, thats probably why they were used even though electric fans were obviously an option!
              Now all of the early V8 models, the V8, S4/S6 Plus and the A8 used a viscous fan of what I will call a paddle type. I am not sure of the dimensions but they clearly have rather wide blades from the look of it. Whereas on the C4 S6 5 pot where space was an issue they used a somewhat narrower fan. The other differences are that the V8's basically had a one piece shroud incorporating an additional 280mm electric fan whereas the C4 S6 5 pot used seperate shrouds for each fan. I have measured the viscous fan shroud at about 30mm deep and the fan aparture is approx 400mm. Now we know the C4 rad is too wide but it is very similiar in depth so I think it might be possible to adapt those components as a very large /slim package. It would also be turning what at present is a handicap, the boss for the original fan into an advantage.
              Of course all that assumes there is actually enough room for a fan that size. We cannot move the centre of the fan and even the shroud aperture is offset to one side. You would have to weigh up the theoretical disadvantages against the benefits of having a car you can use without overheating.
              If you check out the following it might give you some idea of what I am talking about:
              4A0121301 Fan
              4A0121207 Shroud
              4A0121207B Electric fan assembly
              I am not aware of any complaints about the S6 cooling being inadequate even on modified vehicles. The components are also used on TDi vehicles so should be easy to source. I don't know if the thread on the boss is the same for all the Audi models. In an ideal world it would! They would need investigation.
              So basically I am suggesting duplicating where possible the S6 5 cylinder set up in principle. One large but slim viscous fan and a supplementary smaller electric fan.
              Just a thought!

              Looks like the fan is 363mm diameter which is encouraging. Not sure why it would need to have such a wide gap in the shroud .
              Last edited by twoqu; 30 October 2018, 19:05.

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              • Reading the above on fans and shrouds the S6 5cyl is indeed a well cooled efficient setup one that never overheats on standard cars or modified chipped cars in my experience. The viscous fan as mentioned above is obviously very good at doing this, also of note 5cyl S6 cars never suffer with excessive under bonnet heat like the S2 with all it's components crammed into a tiny space and lack of a viscous fan. Seams a viscous fan could be the way to go?
                96 URS6 plus speck saloon
                96 URS6 plus speck estate
                94 2.6 80 Avant
                99 2.8 final edition Cabriolet

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                • So I've been speaking to Pro Alloy and they've been really helpful. First job for me was to make myself a mock radiator to get an idea what I'm up against, first version was a 43mm twin row core but Pro Alloy suggested upping to 50mm twin row so modified my mock one. I wanted as much of the radiator below the bumper line as possible to get the most out of the lower vents, unfortunately the V6 cross member gets in the way of this. Sourced a different cross member which helped move things forward but when spaced a bit further forward really helps. I've ordered some box section to make my own cross member that will let me push things forward and give me the clearance I need. I had an old V6 cross member so chopped that and might use the ends as mounts for the radiator.



                  From the back of the radiator to closest obstruction is about 75mm, roughly measured using a Revotek slim fan that would leave me a shroud depth of around 20mm but might be able to get another 10-20mm depending on the actual fan locations. Interestingly Pro Alloy say I'd ideally need a 30mm depth of shroud to be effective and with the space or lack of between the shroud and engine that I have they are suggesting not to bother with one. Before committing to loosing the shroud I need to finalise the cross member and mounting arrangements so I can get more accurate dimensions to work from. Going to fine tune my mock radiator with the increased width on the ends to replicate the tanks also. At this stage I'm not sure if dropping back to a 43mm core will make the shroud do able, hopefully once the cross members done and a decent mock up I'll get the answers I need.

                  With the bumper on it sat slightly too low inside the bumper so I've taken 20mm off it, also put a radius on the top corners so it sits better under the slam panel.



                  Looking at it I think I'll be going single pass but depending on how it is to plumb they can do it dual pass if required.

                  Probably a stupid question but does the hot pipe from the thermostat not usually enter the radiator on the top and exit cooled from the bottom? Hadn't really paid much attention before but the V8 seems to be the other way around.

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                  • Looks a good solution you have there,

                    Pipe from thermostat on the I5 goes to the bottom of Main and Aux Radiator.
                    Are you going to pipe from thermostat to nearside bottom of radiator with the temperature sensor nearby and the two top ones going in the top offside corner as before?
                    Bypassing the cooling fan speed resistor as its designed for original fan would allow your aftermarket fan to run at full speed at 90deg instead of waiting for second stage which is closer to 100deg.
                    If you can run two fans you could have the big one starting at the 90deg setting and the second smaller one working on stage 2.
                    The other option is the more modern fan control on the emerald ECU would enable you to adjust set point to give you better fan control when in traffic.

                    Hopefully all your good work is going to keep you cool next summer


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                    • So I have a 90 states coupe, running an S8 AKH motor. I had to add all the B4/late coupe cross members, hood, etc. I have a modified front V6 front bumper. The trans is a 2002 FYF 01E with a .56 TDI 6th gear and the upgrade 1 and 2 gear shift collar. Running a stock S8 flywheel and using the oem sensor on the trans. I did not do the motor install, but had it done as I am not a welder and can't do electronics(as in aftermarket ECU) worth a damn. I was using 034 ecu and now run VEMS. I too had a problem with cooling because of the radiator that was installed.
                      So I had one made. It is copper core, brass end tanks, dual core and triple pass. This radiator was made the same size as the V6 radiator, except dual core. I had the upper stock mounting piece of the V6 radiator brazened onto the top of the core. That way I use the upper stock mounts in the original location.The stock A/S8 hose from the heads, I flipped it and it goes to the left side of the radiator. Instead of using a 90 degree hose, I had a 90 degree bend inlet brazen into the end tank. I overflow line is right above the inlet. On the right side of the car at the bottom of the radiator, I had another 90 bend outlet brazened onto the bottom of the end tank. This one has a long straight extension added to it, so I would not have trouble with clearance where the alternator pulley is. I used the stock inlet hose going to the thermostat housing, added a sleeve and found a hose with a 90 bend in it, to get to my lower extended outlet.
                      I am using a Spal 12in fan in about the same location as yours, but I added two A4 AC fans to the front of the radiator. The Spal and one of the A4 fans is run of a relayed radiator sensor. The fans are set to come on at 93C. The other A4 fan runs off the Auto switch on the AC unit in the interior.

                      I just finished up 3 track days at a local track. During the middle of the day, ambient temperature was about 75F. After a hour sessions, temp gauge read right around 90C. My oil temp was higher than my water temp. Temp would go up after the session was over, but never even got to the two dots on the water gauge. So while running, the car never got hot.


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                      Last edited by 90quattrocoupe; 25 November 2018, 17:27. Reason: grammar.
                      They can have my car when they pry my cold dead fingers from the steering wheel.

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                      • I shrouded the bottom and sides of the radiator. For the top, I used the upper piece of the fan shroud, and attached the hood seal to it. I used another hood seal and modified it to fit the front top edge of the radiator to fit under the top radiator mount piece. All air that comes in the front center of the car goes through the radiator.
                        I have had no problem with bumper to bumper traffic in California, on the hottest days in summer.
                        They can have my car when they pry my cold dead fingers from the steering wheel.

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                        • If you are looking for a core. The early V8s came with a dual core radiator that is pretty close in size to the V6 radiator. It is a hair longer and not quite as wide.

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                          They can have my car when they pry my cold dead fingers from the steering wheel.

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                          • I now use a series Audi 80 radiator from the 1.8l ADR Cabriolet. The radiator is identical in dimensions to the standard V6 radiator, but has all the water connections on the driver's side.
                            Advantage of the original radiator is that you can install the series air ducts. You can tell that clearly at the temperature.
                            However, there are still 2 large blowing Spal fans and the small fan falls away.

                            Enclosed pictures of the implementation.
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                            • Nice work, and I see you kept the ABS, tricky to move?

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                              • Not updated for yonks but still determined this will be on road this year so been cracking on with bits and bobs.

                                So after a lot of measuring and testing with various mock radiators Proalloy made me a lovely big, 50mm thick, dual pass radiator with a shroud on the back and double fans.




                                As I had pushed the rad as far forward and down as I could safely get I had to make a new cross member and some mounts for the rad and oil cooler, they took me a while but turned out well. Got some coolant in it last week and ran it today, started first time and idles well, sits comfortably at 93 degrees with the fans coming on/off occasionally so really happy with that. Just need to see if I can make up some shrouds for the sides now. Haven't driven it yet but with a lot more of the radiator getting clean air I'm confident it'll be good.
                                The RR day also showed up a fault with my wideband sensor, the ecu wasn't seeing it properly. Tackled that today assuming I'd made an **** of wiring it, turns out I hadn't plugged it in to the controller :headbang: At least it was an easy fix.




                                Sent my V5 away last week to be updated, going to head back to SOS motorsport to get the wideband set up properly and he can MOT it whilst there, some insurance and I'll be good to go, that's the plan anyway!!

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