Hello to all.......
Endlessly fascinated by the myths and urban rumours about the fluid in LC processors........
1) Forget what colour it is - that's just a dye- usually red, green or blue.
2) The coolant is about a 10 or 15% mix of Ethylene Glycol and distilled water.
(commonly used in your car as anti-freeze.)
3) Quality anti-freeze is based on Ethylene Glycol, but cheap stuff has a high content of Methanol (Meths). Hot Glycol/methanol will corrode aluminium components over time, so......
4) Closed circuit cooling systems (cars or computers) need a corrosion inhibitor to be in place - which is almost always in a commercial antifreeze - the stuff used is normally Sodium Benzoate a soft lightweight crystalline material but very soluble. This may be present at 5% by weight.
5) If you get a leak, the coolant seeps out and evaporates leaving a crystalline mess in the vicinity - this is for the most part the Sodium benzoate corrosion inhibitor re-crystallising out as the water evaporates - the green or blue colour being traces of the dye used. In the presence of Oxygen you will get some aluminium oxides forming as well (off-white slight 'Gel' appearance).
If there is a sticky 'oily' deposit in the area that'll be residues of Glycol which has quite a high boiling point. Methanol from cheap coolants will have long since evaporated as it has a much lower boiling point than water!
Cleaning up a leak ASAP is therefore important as oxygen getting into the (now empty but damp) system will cause corrosion on the Aluminium and nickel plated surfaces.
6) LC G5s had two types of LC system and if you do start to get a leak it'll be preceded by excessive untypical fan noise (frequent on/off whooshing) and probably some gurgling noises when the pump kicks in (air being circulated). The top CPU is the one to suffer the effects first and to a worse degree than the lower one as air will tend to collect at the high points. Eventually they will both 'cook'.
While each CPU does also have a thermal conduction pipe (copper) to the secondary (dry) air-cooled radiators at the back, these alone are not enough to do the job effectively without the LC system running ..... so ignoring it is therefore not a good idea.
Later LC Macs had an absorbent drip tray underneath the CPUs - but early ones did not, and as such a significant leak on the earlier machines can and will drip into the PSU underneath - which can be very hazardous.
7) Removal of the CPU block is the best way of examining for leaks - IF you feel you have the skill / time / tools to do it (static mats etc etc !). Some machines suffer from cracked or rotted connecting hoses which is fairly obvious and easy to rectify, but I have seen quite a few Delphi types where the rubber 'O' ring sandwiched between the heat exchanger housing for each CPU and the heat transfer plates starts leaking, resulting in poor cooling and a build up of 'mess' just visible in the gap between the bottom of the pump plate and the CPU boards.
This can be carefully dismantled, scrupulously cleaned and re-assembled with a high quality 'liquid gasket' compound to supplement the sealing O-ring. This is not a job to rush or tosh buckets of sealing goop around in a haphazard way...... neat and tidy does it.
Tightening of the 4 screws on each of the heat transfer plates on re-assembly should be done gradually and evenly to prevent warping of the plate or plastic housing beneath.
8) Re-priming the system - should be done with before the CPU modules are re-attached (they just make it harder / more risky if in place).
The trick is to have some freshly mixed coolant ready and some suitable sized hose (about 10mm internal dia). The Delphi system has a bleed valve at the top of the radiator covered by a plastic screw on cap. Once removed, the valve has a sprung-loaded ball inside which can be depressed with a suitable sized probe in order to release air.
A good-sized towel under the assembly is a good idea at this point.
I rigged up a 'header tank' some 2 foot above the assembly to give some head pressure and attached this to the radiator's top hose (capping off the rad's now open pipe temporarily. Depressing the ball in the bleed valve lets air out ( a bit like bleeding a CH radiator).... Rotating the assembly about a bit helps encourage air to the top of the radiator where you should keep the bleed valve as the highest point in the system (so the air collects in that high point).
I suspect that during manufacture this 'snap-on' bleed valve is attached to a rig that both evacuates the air and then releases coolant to be drawn back into the evacuated system, but that's a bit difficult to fabricate although not impossible.
Once you have the system full of coolant you'll need to re-attach the pump to radiator top house - this will inevitably lead to a small leak and a few air bubbles getting back in....... I can't advise on the best way to do this but use common sense...... keep the hose at a high point, make the transition quickly and if you don't lose more than a few drops of coolant your probably going to be OK as I can't see that the odd ml of air at the top of the system will be catastrophic. If you lose a lot of coolant - redo it and refine your technique on reconnecting.
Re-attch CPU modules with some good quality thermal paste between the dies and heat transfer plates (don't go mad!) and carefully and evenly re-tighten all the screws.
Put assembly back in the Mac, double check everything is back, fire it up and with luck you're in business.
Well - that's it, mine worked OK but I did take note of the untypical fan noise and caught it before it completely dried up and cooked the CPUs.
For the next week or so, keep an 'ear' on the machine for any recurrence of odd fan noise and pop the CPU cover plate off occasionally and have a close inspection for any further leaks.
ANY serious leaks above the PSU and you MUST power it off and remove the mains lead.
Best of luck!
John H
