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PowerMac G5 Quad "The New Blood Mod" - A guide to flushing, modifying and refilling the dual-pump cooling system.

CircuitBored

Well-known member
actual part numbers or links to the parts would help

Here are links and part numbers for all the parts that are not self-explanatory. Some of these parts are generic and do not have part numbers.
Apart from the Eisdecke pump-tops all of these parts can be swapped out for similar products from other companies, those are just the ones I chose for my build. If you need help finding parts in your locality then let me know.
 
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danyetman

Member
Here are links and part numbers for all the parts that are not self-explanatory. Some of these parts are generic and do not have part numbers.
Apart from the Eisdecke pump-tops all of these parts can be swapped out for similar products from other companies, those are just the ones I chose for my build. If you need help finding parts in your locality then let me know.
That's very helpful. Thank you.
 

danyetman

Member
My pleasure. Please post pictures in this thread (or create your own!) if you end up doing this mod. It's a big and complicated job so I wish you luck!
Err, your link to the Eisdecke tops is wonky.

But I have two dual pump Quads, and I have plans to refurbish and max out both.
 

dorkshoei

New member
@CircuitBored Thanks for the pics/writeup. I'm taking mine apart at present.

I'm actually having serious issues with my Quad, detailed here. To be honest I'm not expecting this cooler rebuild to fix the chronic open-firmware instability and inability to boot ASD issues though maybe re-applying thermal paste on the Northbridge (next step after I do this) will; hope springs eternal as they say.

But clearly I also have a cpu cooling issue

I noticed you removed one of the oval ended nipple caps too. I wasn't expecting it to be quite so packed with epoxy underneath. Looking it seems you didn't attempt to clean up any of the old epoxy?

I've done lots of radiator work before. I'm pondering keeping the stock pumps as I'd rather keep the G5 cover. I have some ideas on how to bleed the system.
 

dorkshoei

New member
Oddly I only got 250ml out of both of my radiators. Before I disassembled I could hear coolant moving if I shook the assembly which implied the presence of air. No leaks.

I'm flushing them using a submersible pump and a warm vinegar solution and I definitely appeared to have a blockage on one side, however it cleared fairly quickly.

The pump rate is fairly low, 5.6 liters per minute and that flow cannot be sustained through the radiator. I'm not seeing any debris. I'll have to try the 1/2 fill, connect input&output and shake method. See if anything comes out then.
 

CircuitBored

Well-known member
So sorry I didn't reply sooner! Notifications for this thread had automagically turned themselves off.

Looking it seems you didn't attempt to clean up any of the old epoxy?

No I did not, for the simple reason that it is there for a reason, and if it ain't broke...

As was mentioned over on your MacRumors post, the temp sensor itself can fail, sending the Quad into panic mode even though all is well.

I have some ideas on how to bleed the system.

I am super curious about this - please do share, along with your progress elsewhere! My Quad has been running super smoothly ever since I did my cooling mod but I am tempted to bite the bullet and replace the thermal paste again soon. I'll wait until winter, when the Quad serves as my lost crypto wallet password cracker/space heater. It is far too hot for me to run a Quad at the moment!
 

bkmoore773

New member
This is a repost from the "G5 Quad w/rebuilt LCS will not overheating thread", but I am posting it here so my notes are easily available for anyone attempting the New Blood Mod. I purchased a G5 Quad from the local classifieds. I was actually looking for an air-cooled dual G5, after reading all the problems with the LCS. The seller had no idea as to the specifications. When I inspected it, it was a Quad model with the dual-pump LCS. I bought it anyways and inherited a small boatload of trouble. The LCS showed no signs of leakage, but wasn't able to effectively cool the CPUs. After running a few days, the system overheat and the red LED came on. I did some research online and after considering all my options, I performed the "New Blood" Mod as described above.

Although my unit still hasn't passed a thermal calibration, I consider the mod to be successful and am sure after some additional steps my G5 will pass calibration. My G5 now runs cool, the fans are quiet, and it doesn't shutdown due to overheating. In short, it's a 100% useable computer. This mod isn't plug and play, but should be doable for anyone with some basic tools and skills. The main thing is to be patient and not to expect everything to work perfectly right away. It seems my cooling system is performing better now than when I first performed the mod, it may take some break in running to get everything running. I only had the LCS apart once, choosing to trouble shoot it rather than re-do it.

Some Lessons learned so far:

1. The original cooling fluid has a lot of sediment / contaminant. If you get an LCS G5 and the LCS hasn't failed, it will fail and will not be able to regulate the CPU temperature under load. This can be due to: dry thermal paste, air in the LCS, mineral deposits on the inside of the heat exchanger, failed cooling pump, blockage in the circulation system. Leakage isn't the only failure mode and a dry LCS isn't necessarily a functioning LCS. Below is a photo of the original cooling fluid that I extracted from my LCS. All that sediment cannot be good for cooling efficiency. Do you want this stuff in your G5?

IMG_9191.jpeg



2. Incorrect assembly can keep the CPU from cooling properly. I damaged one of the spring-loaded pins during reassembly. My G5 overheated immediately. I had to find a new pin and reinstall the CPU. The cooling surface is very small, there are no heat spreaders. You need quality thermal paste and need to apply it correctly. I recommend spreading a thin layer on the CPU. The spring-loaded mounting pins must be evenly and fully seated to ensure even pressure and 100% contact. We are dissipating over 100W in less than a square inch of surface area.

3. The LCS needs to be cleaned out. Mineral deposits can form on the inside of the radiator and act as an insulation layer. Ultrasonic cleaning would get rid of any mineral deposits on the inside of the radiator and heat exchanger. Another simpler idea may be to add 50% vinegar and run the computer for a few days, then replace the cleaning fluid... That's what I would do on an old car radiator.

4. Air bubbles can form in the LCS at any time. After performing the mod, my CPU B was 20C warmer than CPU A. I couldn't figure it out for a long time, suspected all kinds of things from incorrect assembly, see 2, to defective CPU card. I swapped the CPUs A and B, no change but ruled out a defective card. The cause was air bubbles. I thought I purged all the bubbles when I filled the LCS...I was sure of it. Then I ran the system for a day, and found lots of air bubbles on CPU B. Run your computer for a few hours, then inspect for air bubbles. Purge as necessary. Run again and reinspect. Run the system in different orientations to find the air bubbles, i.e. vertical / horizontal. Run it with the lid off so you can see the air bubbles. Put in a guitar pick to keep the fans from going to 100%. Sometimes just turning the system on, the initial suction effect of the pumps will reveal an air bubble.

5. If your system doesn't pass thermal calibration right away, don't get frustrated and tear the LCS apart. If it's not overheating, run the computer and enjoy it. Or put it away for another time. Look for air bubbles, see 4. Check your assembly, see 2. Not passing thermal calibration doesn't mean the LCS doesn't work. It only means it cannot keep the temperature regulated at 70C or less under full load. Don't keep trying to run calibration on a defective LCS. Find the root cause, correct, then rerun calibration. Also ambient room temperature has to be below 77F for calibration to work.

6. A simple mod: I put a strip of tape between the fan assembly and the heat exchanger. This forces all the air into the heat exchanger, because we removed the CPU cover plate and I noticed quite a bit of air was leaking out the sides. This seems to drop the CPU temperature by another degree C or two.

IMG_9193.jpeg

My G5 is a work in progress. I haven't passed a thermal calibration yet, but am very close. My next step is to replace about 50% of the coolant with vinegar, then run the system under load for a few days. Replace all the cooling fluid, then reattempt thermal calibration. If that doesn't work, then I'll consider getting an ultrasonic cleaner. But that's about $150 for the cleaner, but I know if I bought it, I'll find many more uses for it.

The Quadra G5 is an awesome computer and I believe worth saving. I also have a Pentium 4 from 2005 and the G5 blows the Pentium 4 out of the water. It's not even close, and is like comparing a vintage Boeing 747 with a DC-3. I can think of no other computer from 2005 that's as useful today as the G5 Quad. Overall I'm happy with my G5 Quad and expect to get many years of enjoyment out of it.
 

Byrd

Well-known member
@bkmoore773 thanks for posting up your additional tips along the way.

I'm still at boat anchor stage - two Quad G5s (one single LCS, other dual Delphi LCS - one was bought for parts but short of new cooling both are OK); pumps replaced with aftermarket units, loop rebuilt and ... pumps flow is clearly impeded by something in the radiator or CPU blocks. Argh; likely to be a summer job late 2022 :D
 

CircuitBored

Well-known member
6. A simple mod: I put a strip of tape between the fan assembly and the heat exchanger.

This is a really nifty idea. I was actually pondering the other day whether or not the missing G5 faceplate and air baffle had an effect on thermals and I guess this is a partial answer to that question. I wonder if it would be possible to devise a new baffle that allowed for the taller pumps. My wacky idea was to laser cut some holes in the original baffle. I have a spare that would be a good candidate for fiddling.

It is so, so cool to see my idea being applied to other people's machines.

Thank you so much for sharing all of this!
 

bkmoore773

New member
I read the OP about shaking the LCS with warm water and vinegar in it, but it seemed easier and probably more thorough to just run the whole system with this mixture. Also, I have no desire to remove the CPU, reapply thermal paste, etc. and do all that again. Last night for experimental purposes, I used a syringe to remove about 50% of the red coolant and replaced it with distilled white vinegar. It actually passed thermal calibration for the very first time with the 50/50 vinegar !!! The system was running like new, even under full load both CPUs were below 70C. I ran it overnight.

The temps on CPU B started to get above 80C this morning I put the G5 upside down between two chairs, oil pan underneath, and drained all the coolant from both cooling loops. There was some residue in the drained fluid. I completely refilled the LCS with 50% distilled water and 50% distilled white vinegar (no EC6 coolant). The system is now running on this mixture and is actually running quite nicely. I'm running at the highest performance setting and putting the CPU under loads. CPU temperatures are all below 70C. I'll run it like this until the temperatures start getting high again, or for a few days. If it runs stable, then I'll flush it with water and then put in proper cooling fluid. If the temperatures start to climb above 70C, I'll drain and refill with 50/50 water and vinegar again, repeating until the temperatures are stable over time. I think with this approach, I should be able to get the heat exchanger cleaned out while also using my G5.
 
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