Troubled G5 - Overheating issues?

[cjtmacclassic]

Hello all,

I just recently got a G5 (dual CPU, 2.7, 4GB) with a few caveats. It has trouble booting, and if left to sit, the fans rev to max speed but the system doesn't boot (a red LED glows near the lower CPU as well). If forced to shutdown during this cooling frenzy and powered on again, it will boot normally. Idle temperatures are around 130-140*F on the CPUs. If tasked with anything beyond idling, the system will fan erratically, then sleep. I am not at all familiar with the quirks of this model, but I'm leaning towards cooling issues. I hope you'll forgive my noobishness if this has been answered before. From what I've read, I'm assuming I need to replace the thermal compound and flush/refill the LCS.

Any advice is, as always, very appreciated

 

[360alaska]

dual 2.7s are notorious coolant leaks due to failed O-rings, I've rebuilt a couple LCSs so far it's actually pretty easy.

 

[waynestewart]

Aside from coolant leaks, they also plug up with dust. I was given a 2.5 that was overheating badly. After blowing out a huge amount of dust it's been running well.

 

[beachycove]

Quality heatsink compound, properly applied, makes a great difference on a G5 too. However, that problem's more likely due to an LCS that needs flushed and rebuilt.

The good thing is that the machine boots, so it hasn't obviously been totally ruined by a leak. It'd thus be worth having a shot at fixing. There are some how-to-rebuild guides specific to the early LCS G5s out there if you look for them.

 

[techknight]

and dont forget the all too common BGA failures on those system boards. 

 

[cjtmacclassic]

Alright, looks like I'll be investing in a LCS rebuild. I'm seeing "white rice" near CPU B. I've found a guide on xlr8yourmac, but I'm having trouble locating suitable o-rings. Does anyone have a recommended source for these?

 

[unity]

I took will be looking for o-rings. I am pretty sure Fastenel stores in my area can order them, or Grainger. But they will be in bulk. If I end up ordering some time soon I will let you know so we both dont end up with more than we will ever need.

 

[beachycove]

A couple of years ago, I bought small o-rings for something like 50 cents apiece for an old outboard motor carburetor rebuild. Rubber is not able to withstand the chemicals found in fuel these days, so ordinary plumbing o-rings were no use. I found the fuel resistant variety at an industrial/ hydraulics parts place. They had them loose in a box, with small and mostly large ones mixed together.

All they've got to be is the right size, antifreeze/coolant safe, and heat resistant. Presumably the material would be some variety of silicon?

 

[cjtmacclassic]

The guide lists ethylene-propylene as suitable for G5 temperatures, though I imagine silicone would hold up even better, so long as it doesn't compress too much over time. Maybe I could do some tests at length and find out what's most resilient?

Unity, I'll keep looking for those o-rings, but if you happen to find a source, I'd be very much interested in buying from you.

 

[360alaska]

Use Prestone Green with 20% concentrate for Dual Processor LCS, I only use silicone based(DEX-COOL) for the Dual PUMP QUAD LCS because that's what they originally came with. I would not recommend using silicone based in the dual CPU LCS simply because it was not designed for silicone. If you want to keep this mac a long time you'll have to do this in another 3 years potentially...

 

[unity]

I would just stick with proper coolant, not Prestone. Its not expensive after all.

 

[360alaska]

What do you consider proper? Prestone green is Ethylene glycol so...

 

[unity]

I consider this proper:

http://www.newegg.com/Product/Product.aspx?Item=N82E16835103048&Tpk=N82E16835103048