Water Cooled PowerMac 2.5 GHz G5
Coolant Leakage & Corrosion

There have been many reports of coolant leaks and subsequent damage to Apple G5 PowerMac computers. There is also an effort to create a database in order to document this problem and get help. A recent very detailed investigation by EagleFour gave me the final push to investigate my own 2 X 2.5 GHz PowerMac.

I got the machine new from a reseller in summer 2005. It was manufactured in Feb 2005 in Cork, Ireland. It runs continuously at full load, performing scientific calculations.

Because of the many web reports on G5 coolant leaks, I recently decided to open mine and check for problems. This was also motivated by white deposits on the rear "foot" of the case. At the time I was not sure if this was due to leaks, now I am sure!

I followed the procedure of EagleFour and the Apple guide, which is linked on the EagleFour site. The only difference was that I also removed the bracket stabilizing the heat pipe radiators, at the rear of the CPU/cooler unit. This gave better access to the rear center screws holding the plate to the chassis.

CPU HeatSinks
EagleFour found colored solid deposits on the edges of the CPU heat sinks. I found this as well, but the amounts were smaller. I removed them with a small screwdriver, as well as possible. Solid material had not become so extensive as to contact components on the circuit board below.

Power Supply
EagleFour either did not investigate the power supply, or it was OK. Due to many reports of "exploding" power supplies (loud bang), I decided this was the time to check it.

There was a gray, flaky, multilayer absorbent material on the power supply cover plate below the CPUs. This is apparently the "diaper" noted by others. When I went to unfasten the screw below it, I noticed corrosion on the rear of the plate, under the plastic holding the diaper. Now I knew I had a problem!

Power supply cover plate and "diaper"

Power supply cover plate partly removed, in the foreground. Note the corrosion under the plastic support of the gray absorbent fabric ("diaper"), at the rear of the plate. Also visible is corrosion on the top of the power supply itself, around the cable (which has been detached from the logic board).

Power supply cover plate 2

Another view with no flash to better appreciate the corrosion and absorbent fabric.

Next I removed the power supply itself. The appeareance suggests a minor problem:

Power supply 1

Bottom of the power supply, showing how leaking coolant had spread under and around it, leading to extensive rust. Note the white deposits on the edges, this appears to be from the coolant.

Power supply 2

 Rear of the power supply, showing how leaking coolant had spread up the perforated region as well.

Now I feared the power supply was dangerously damaged, and opened it with trepidation. Fortunately (for safety reasons!) the liquid had not yet reached any components on the circuit board. However, it was very close- a mounting screw was badly corroded, it was probably not long until electronic components were damaged.

Power supply inside

Inside of power supply.

CPU / Cooling Block and Pump Leak
Initially I could not understand how such extensive corrosion had occured. It was difficult to see until the CPU and power supply cover plate were removed. Inspecting the CPU / cooler unit, I also could not find any obvious source of such extensive leakage. The small leaks on the CPU heat sinks were clearly insufficient, and no residue was present on the circuit board. I think a serious leak here would quickly destroy the CPUs.

Only when I inspected the block more carefully did I notice the path of the leaking coolant:

Pump leak 1

Liquid track beneath coolant pump.

Pump leak 2

Different light shows the white residue similar to that on the power supply case. The aluminum is not corroded by the fluid, making the track less apparent than on the steel power supply case.

Cause of the Leak and Power Supply Corrosion

Problem 1
The immediate cause was simple:
>>> A pump gasket failed <<<

Rubber fragments

Rubber gasket fragments found under the pump.

Problem 2
A major contributing factor to the extensive damage was that the escaping liquid was not absorbed by the fabric. This was evident from the fact that the absorbent fabric was not wet, nor did it have any coolant residue on it. In fact, there was corrosion under the plastic backing of the absorbent fabric. Why did it not catch the fluid and prevent it from reaching the power supply?

>>> The absorbent material does not extend under the leaking pump <<<

The liquid dripping under the pump does not fall on the fabric, but instead drains down the side of the power supply. This is a clear design error. This potential source of leakage was obviously not taken into account when sizing and positioning the fabric.

Final Comments
Like many others, this experience has left me very disappointed. For years, a justification for the substantially higher price of Apple computers was their quality and durability. I have 2 older Macs, both run, and one calculates 24 / 7. On the other hand it is inexcusably noisy, a Quicksilver 2 X 1 GHz G4, upgraded to 2 X 1.33 GHz. This is also a major design flaw, which Apple "fixed" with liquid cooling in some G5 models.

My experience, and that of others, suggests that owners of liquid cooled G5 computers should take them apart to check for hidden corrosion damage. This inconvenient (Take out the processors to reach the power supply?! Difficult and not good design.) and carries some minor risk, but could avoid catastrophic and very expensive failures and repairs.

Will I buy a Mac again? I dont know. I got a Mini not long ago (3rd Mac doing calculations), because it seemed the only element of the Apple line which had a good price/performance ratio. Then I had to upgrade the processor and memory anyway, but at least it was possible. And rumors persist that Apple wants to kill the Mini.

Im starting to think that I should invest in Linux. And Apple has helped me by providing training on a unix-based OS!