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Good YouTube / Written Guide to Draining and Refilling G5 Quad LCS

mac57mac57

mac57mac57

macrumors 6502a
Original poster
Aug 2, 2024
610
368
Myrtle Beach, SC
Hi All, Per my thread on restoring a hot G5 Quad, I need to drain and refill it's LCS. My efforts to find a really good YouTube video, or a detailed written guide, about how to do this are coming up empty. What I keep finding is stuff for 2.7 GHz G5s, conversion to air cooling for the Quad, and more related, but not on point, topics.

Can anyone point me at a G5 Quad specific YouTube or written guide that addresses how to drain and refill a G5 Quad LCS? Please note that I DO NOT want to replace the existing hoses, which even after 20 years are soft, pliable and critically, are not leaking.

If I can't find a good YouTube or guide, my plan is:

1. Undo the access cap on the LCS and sit the whole thing upside down over a bucket and let it drain.
2. Then, per a guide I saw a long time ago, I will literally hoist the entire thing over my head and "shake it until my arms can't take it" anymore, as a means of getting the last drops out. I believe the guide I saw back then, but can't find anymore, said to shake it like it's life depended on it, which it does, sort of...
3. I will then refill it with a 50/50 mix of vinegar and water, shake it again, but with the access cap closed this time and then drain that, as an attempt to clean it out a bit.
4. Finally, I will refill it with a recommended coolant (I have been able to find some coolant recommendations at least).

Thanks for any and all advice!
 
Have you taken a look at the "New Blood Mod" guide (68kmka.org)? That's the best guide I'm aware of for rebuilding an LCS that's targeted at the Quad. It is a bit more detailed on replacement components but should do just fine if you want to keep your LCS stock.
 
Thanks @Doq, yes I saw that one. That one concerns itself with dual pump LCS units. Mine is a single pump. I'll have another look at it however, just in case it goes into more detail on the actual drain/refill steps. Thanks for pointing it out!

Edit: thanks again @Doq. I read the whole thing, and there are some useful pointers in the flushing and refilling section. It is all somewhat specific to what that particular author is trying to accomplish, but still somewhat useful as well. Thanks again for bringing this back to my attention.
 
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One last question here, before I proceed: it seems that simple distilled water is the best coolant to reload the Quad LCS system with, after draining and a suitable amount of flushing of course.

Does anyone know why this might not be a good idea? If so, do you have a recommended coolant, and why? Thanks!
 
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Thanks @NikolaPPC, I read through the entire piece you linked. It mentions automotive coolant as a possible cooling fluid. I have read that distilled water is best, but I have not seen anything definitive on this topic anywhere.

With automotive coolant, I would be concerned that it might contain compounds that would slowly degrade the existing, original hosing, which was not designed for whatever the latest automotive coolants are.

Can anyone comment on the use of distilled water as the LCS coolant?
 
No problem @mac57mac57!
Yeah it does mention automotive coolant, but only specific ones are appropriate. The problem lies in the design of the LCS itself. The radiator is made of aluminum, the CPU block is made of copper (with some type of rubber fittings), the pump is made of combination of different plastic and rubber. Also the hoses, I've mentioned what kind is the best suitable (heat resistant/smooth EPDM rubber with a high synthetic textile reinforcement).
When you combine all that, the choice for the coolant is very difficult.

If you use just distilled water, pretty quickly the reaction between aluminium and copper will start. Copper and aluminum have widely different electrochemical potentials, so when they are combined in a cooling system, galvanic corrosion will start. Galvanic corrosion (also called dissimilar metal corrosion) erodes the metal, causing leaks over time. Also, the corrosion can clog the pump and CPU blocs (this can lead to a failing of the pump that is impossible to find). The reaction can even cause the rubber in the fittings and plastics to degrade etc...

Everything can also happen if you choose a wrong coolant.
What you need is a specific coolant that is made for this type of application.

The automotive coolant some people mentioned is specifically designed for the cars that have copper radiator, engine made put of aluminum (or iron, with some parts of aluminum), plastic and rubber parts.

This problem is also very known in the PC LCS industry. They make specific coolants for these kind of conditions.
Don't be tricked, some market their coolant suitable for aluminium radiator and copper CPU block, but the reaction still occurs.

Over the years i came to find lots of recommendations for coolants that are good to use, here are some examples:
Thermochill EC6
Swiftech Hydrix
PT Nuke

I will add some more info soon (i have a lot of TXT files on my PC with all sorts fo information, so i have to sort everything first and i will post here all of the information i have). Cheers!
 
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Thanks @NikolaPPC!

I have now opened the LCS itself up by unscrewing the access port (I fear I have damaged the piece that goes in there in the process) and am draining it, which is occurring in large drops vs. a steady stream, which I had hoped for. Now I know why you have to "shake it until your arms can't take it"! I shake for a while, put the unit down in a different direction, let is rest a bit (i.e. let some coolant pool together) and then shake it again. "Rinse and Repeat" until nothing comes out any more.

This is all well and good, BUT, how much came out, in milli-liters (or ounces)? I don't know - I was holding it over a sink while doing this. I *should* have been collecting what came out so I could see how much there was, and then compare that to how much there should have been. And this is the key question, how much has to go back in? Does anyone know what the fluid holding capacity of a single pump LCS is? I am not quite sure how much coolant to reload it with! This is a classic "newbie" mistake; I should have tried to find that out before proceeding!

I will be reloading with a 50/50 mixture of distilled water and vinegar as a cleaning compound. I will run that through manually (more "fill it up, wait 30 minutes or so and then shake it out") a few times until it seems to be coming out completely clean. Then it will be time to reload with actual coolant.

I could not find any of the ones you mentioned, and in the end I purchased this product, which says it is safe for copper, brass and nickel (does anyone have any experience with it?):

71bfsvCpXNS._AC_SY879_.jpg


Thanks!
 
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You probably can find a replacement for the piece/part you broke, but make sure you have a caliper to measure everything properly first.
Yeah, you really have to shake it, vacuum effect happens with the liquid inside the radiator haha

It's not really important how much poured out, but it's probably around 1 Liter (pure guessing).
It's really simple how much should go in-as much as it can :D
What's really important is that you don't let any bubbles be in there. You have to fill it up, let it work on your workbench, when the bubbles collect at the highest spot turn it off, fill it more etc...position your LCS while working in every possible position so you guide all the bubbles in one spot.
If you really want everything in detail, i can send you my discord and help you out. I can't do everything over posts

I didn't understand good, did you clean everything (like whole LCS, pump, hoses..) with vinegar and destilled water?

I'm sorry to tell you, but that coolant is not suitable for mac G5 Quad LCS. It isn't made to stop galvanic corrosion, so you use it at your own risk.
Cheers!
 
Thanks @NikolaPPC, yes, I am presently cleaning out the entire LCS system with a 50/50 mix of vinegar and water.

When I refill, I will follow your advice (thanks!), filling, letting it settle to allow bubbles to form, rise, coalesce and then pop out, and then add more, repeating until full. If you do have a more detailed treatment of the this that you can send me, I would be delighted to receive it, read it and integrate it into what I am doing.

Right now, I am documenting everything I am doing... notes for my own guide, to be published once this exercise has succeeded. If yours is better however, that would be great - instead of publishing mine, I can just link yours! There is no pride/ego here. These machines are rare and getting rarer... the more people that can be taught how to maintain them, the more of them will remain in service. That is a noble goal.

As I clean it, I am seeing very little debris washing out... I am guessing it was simply low on coolant, and refilling should give it a new lease on life. Of course, I am not doing this under pressure, so debris *could* still be lurking in there.

The new coolant may be a temporary step, particularly if it is not the best for this application. Once you have done this once, doing it again is much less challenging. I tore down the entire machine this second time today in just about an hour vs. the day or so it took the first time.

The new coolant I have ordered is good enough for initial testing. I really do want to see if new coolant, or more coolant, addresses the core problem. If the machine runs cooler and quieter after this refill, I can order the best possible coolant and wait for it (weeks, according to Amazon). When it finally arrives, it should be no more than a day or so to drain the old and install the new.

Then I will repeat the whole thing with my other Quad (barely usable these days due to cooling issues) and have two of these amazing machines. I *may* then sell the second one to someone who can provide it with the love and care it deserves.
 
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Hey @mac57mac57
I don't know if the pump should be cleaned like that, but now we will see hahah
No problem! I don't have everything documented. I just know how it should be done, but don't have a lot of free time because life.. to rebuild the LCS again (last time i did it was way back when..), so i leave that part of the documentation to you, i can give you tips over time to include in your main post if you like :D
These stuff aren't about pride/ego, but to help everyone, because we are a small community :D

Take as much time as needed to clean the system, no pressure!

You are right, it is easier to disassemble over time!

I don't think you will notice much difference in temperature with the other coolant (+-few degrees), its just that you will stop the corrosion of the whole LCS and making it fail. Galvanic corrosion reacts really fast and is REALLY hard to clean, like almost impossible, so if you clog the pump, ruin the radiator or even worse, the fins on the CPU block...i dont know what to tell you..

Who knows, maybe use both of them? :D
 
Another question: SOMEWHERE in one of these forums I read a post where the author described how to get the LCS pump to run by connecting up +5v or +12v (or both) to pins on the LCS fan control connector. Unfortunately, I cannot find that post again!

Does anyone recognize this particular post, or simply know how to get the pump in a single pump LCS to run before it is reassembled into the Quad? Thanks!
 
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