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Quad G5 LCS experiment

Posted by: beachycove on 2017-01-04 17:10:35 So the time came to service the LCS on my G5 Quad, which involves flushing the radiator and hoses, renewing the thermal paste, etc. It's a pain in the gluteus maximus. One of the usual problems with these machines is that sediments in the coolant clog the microchannels and associated components in the cooling block. I duly cleaned mine up, refilled the system, and started 'er up — only to have a large temperature gap between the two CPUs. So I figured I'd take the offending processor apart and see what was the matter. On taking the thing apart, I discovered that the microchannels were starting to plug up with sediments again, with the machine having run for no more than 45 mins. The radiator must be dirtier than I had thought, though I used a radiator cleaner and had taken the best part of a day to do the job right first time around.... I then had a brainwave. "If the problem is the microchannels, what if the microchannels were removed?" thought I. I figured that if I was going to have to strip the thing apart again, I might as well do a little experimenting, and see if I could prove something to myself. So, I removed the internals in the LCS waterblock, which is a soft (silicon?) black pad, a hard plastic/ silicon microchannel insert, and a pink foam washer. I've attached a pic of them removed (they are now stored in a bottle of distilled water). I then reassembled the LCS without these internal components, i.e., with the hole where they went empty as in another attached pic. I then reassembed the lot, booted, and what do you know? The thing works perfectly, at the moment at any rate. I've attached a screenshot of the CPU temperatures over a five or six hour period today under varied levels of activity. Iam not sure I will leave it this way, but at the moment, the machine appears to be working as well as it ever did. Temperatures are about normal for a G5 Quad (Processor is set on Automatic). While posting, I took a shot of the current temps in numbers for posterity. Neat, wot? Unfortunately, it fails thermal calibration in ASD2.6.3, which reports that the readings are out of specification. So I have to operate under my previous settings.

Posted by: Unknown_K on 2017-01-04 17:51:23 Those microchannels are for better heat transfer (faster velocity, better stream mixing). If you have issues with fouling clean the radiators and maybe put a filter inline (will need maintenance just like everything else).

Posted by: beachycove on 2017-01-04 18:59:00 Yes, I thought about a filter back when I first overhauled the system 4-5 years ago, but never installed one first nor last. There were actually two tiny pipe-sized stock filters in the plumbing, as shipped from the factory, but I removed those back then because they were plugged pretty solid, and they were completely inaccessible, down by the pump or some such thing. I thought that an occasional flush, etc., would suffice. Unfortunately, that's not the case. As I've got it working now better than it has for a year or more, I will likely leave it as is for a while and see what happens. But if I do go back to the OEM microchannels, I will clearly need to deal with the sediment problem. Whatever were done, I think it would be done via an extension into the upper bay, so as to make servicing less of a hassle. A filter is one option; another is one of those little acrylic fluid chambers, in which sediments could theoretically be expected to collect in the base...so they could then essentially be vacuumed out with a syringe or drained away.

Posted by: Unknown_K on 2017-01-04 21:55:17 Some filters can be unclogged if you back flow them (pump water the opposite direction), but new filters are the way to go.

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