• Water temperatures and flow rate: how can I find these out, please?
• Correct, 3 fans at the front on the radiator, and 1 larger at the rear of the case. I believe the three fans on the radiator are pushing air out, as far as I can tell by the draft. Not sure about the one at the rear.
• The fan at the back: no idea.
• Radiator model and size: not detailed on the list of components I received from the assembler (the invoice just says "Watercooling system").
• CPU Core Temperatures: 38-56C at mostly idle (instant load average 3.52, for 6 cores hyperthreaded)
  julien@supercompute:gpu-burn ((v0.4.5))$ sensors
  coretemp-isa-0000
  Adapter: ISA adapter
  Physical id 0: +56.0°C (high = +90.0°C, crit = +100.0°C)
  Core 0: +52.0°C (high = +90.0°C, crit = +100.0°C)
  Core 1: +38.0°C (high = +90.0°C, crit = +100.0°C)
  Core 2: +56.0°C (high = +90.0°C, crit = +100.0°C)
  Core 3: +48.0°C (high = +90.0°C, crit = +100.0°C)
  Core 4: +56.0°C (high = +90.0°C, crit = +100.0°C)
  Core 5: +40.0°C (high = +90.0°C, crit = +100.0°C)
  

Scarlet-Tech
You have a 360 radiator cooling 5 components?  
 
You should have a MINIMUM of 120mm per component, so 5x120 or 600mm equivalent, and then you should, if possible, have 120mm extra, for 720mm total.. You should have 2x360 radiators at least.  
 
You should provide more pictures, because what you show currently, you should not have that many components on just one small radiator.  Whomever built that, didn't do what they should have.
 
Also, is the pump built into the radiator?  If so, is it at the top of the radiator right now?  Lastly, are you getting good water flow while it is on or does it get bubbly and loud?  You can see in the picture that I attached that there is already bubbles in the line, circled.
 
 
What company did this?  Your rear fan is clearly blowing in, and you stated the front fans are blowing out (through the radiator?)...  

wmmills
Was there controller software for the gpu/cpu cooling system they installed from whichever manufacturer? You need to control those rad fans when in different situations to get the cooling you need cause the temps are def high. You can always get a custom fan controller and mount it anywhere in/on the case and have direct access to the fans and bypass windows entirely, if that appeals to you. Everything looks good from here in NJ,...... im just kidding man. :P  :)   Seriously, from what i can see its looks done well. With four cards together like that, even on water, the pcb boards still release heat, so some ambient air circulation def needs to be run thru the box, which it looks like they did. Im not a big fan of rads on the inside of a case with other components, theres just too many issues and the cooling is not optimal since your pulling heated case air through a rad. They need there own section of the case that's sealed off from the rest of the components or a external custom mount if necessary. @Scarlet.... they were probably thinking that because they were cooler running 10xx series with lower voltages the typical 1 120/Compo wasn't as necessary, especially if he wasn't going to be benchmarking, gaming or overclocking. As far as the bubbles, i cant tell!!! lol. I cant tell if its bubbles or just the tubes reflecting and distorting the gcards pcb solder pinouts on the backs of the cards. Another photo with a piece of L shaped cardboard covering them would be great, right?!?  :)
 
Edit: I just realized something else while looking at the blowup in Paint, shouldn't the tube going out to the gpu's be in the lower left corner of the cpu block, not at the top left, so your working with gravity and not against it pushing the water up to the top corner?

loveha
Also if I am not mistaken, shouldn't that top fitting on the water bridge be the left port?

bcavnaugh

loveha
Also if I am not mistaken, shouldn't that top fitting on the water bridge be the left port?

 
For Parallel it would be OK, but Not for Serial.

• Pics: I have uploaded extra pictures below, including zoom on the fan's label.
• Fan size: 120 fans on the front, 1x160 (or 150) at the back. I'm not sure if there are 3 or 6x120 fans on the front: on the pictures, it looks like the front fans are on both sides of the radiators, which would make 2x3 = 6 fans. Does that look like it to you too?
• Fan direction: the 3x120 fans on the front were definitely blowing air out during the test (I was feeling the draft of very warm air). The case is sealed at the top. The front fans blow against a plate that then has vents on the sides (ie not straight open in front).
• Tests with case open: I've just flown out of the country for 12 days (going to NIPS machine learning conference next week), so won't be able to do other physical tests before then. Only software tests over SSH :/ [unless I ask my wife to open the case...] Longer term this machine will sit in a datacenter of an NGO I'm helping, not at home, so I'd much rather have it safely closed rather than open-hearted.
• Black bands: The black bands are indeed just ties to hold the pipes cleanly out of the way.
• Bubbles: Thanks for suggesting to check for bubbles : there are none at all, these were just reflexions due to my atrocious photo skills :) I double-checked.
• Pump flow: I do not know of any way to check the flow or the temperature of the coolant, or to set it.
• Assembler name: I've just contacted the assembler today to discuss. They have a very good reputation for gaming rigs, and are very friendly, so I'd much rather give them the chance to be their usual awesome and then sing their praises once they've fixed this, rather than naming then now before they've even had a chance to look at the problem :)
• Assembler's answer:  Right now their first answer is that these temperatures are safe and normal on high load (as opposed to gaming), but that I could force  the fans to 100% all the time, because the fan speed depends on the CPU temperature which could be small (except that it the CPU was at 70 in the test). I will point them to this thread to see advices from more knowledgeable people than me. 

• really quiet , otherwise my better half is going to be very sad of having our living room super noisy. The slower fans the better, the more noise-proofed case the better too.
• Watercooling the 4 GPU *and* the CPU.
• ideally temps of 40-55C on full load. I don't need ultra cool capacities, but these babies are going to work a lot (machine learning applications)
• I do *not* plan to overclock.

• Case:
  • @AHowes, you suggested Thermaltake Core X9. Will it be enough for Quad-GPU?  
  • Separate fans compartment seems great, but is that compartment silenced? The assembler  suggested to not use it as it's not silenced, and to put the fans in the main part of the case. Does that make sense to you?
• Fans: how many, what size? brands?
• Radiator: what size? do you recommend brands?
• Flow monitoring: do you recommend temperature sensors, flow sensors, in the loop?
• Anything else : am I forgetting anything?