"I would have sent this earlier but had problems last month with this Mac Pro that I thought were related to the CPU upgrade, but luckily turned out to be caused by broken NB heatsink plastic rivets. (past notes here.) Didn't think to check that initially as they were still intact when I upgraded the CPUs but wish I'd replaced them while I had the CPU heatsinks off or at least done a wiggle check to see if they were brittle.
  For the CPU upgrade, I used the tips and info in this previous report on heatsink spacing problems (and wiring note) that came in handy although I used 2.93GHz quad-core CPUs (X5570's?) locally from someone doing a dual 6-core upgrade.

Now that I know all this, keeping an eye out for CL sales of similar Mac Pros with problems. Fixes may not always be that simple but I think as time goes by more 09 mac pros may have this problem. Some owners may get high repair estimates and decide it's not worth it to fix and just buy a newer Mac instead. But I'm glad to have a model that has more DIY upgrade options and can still run SL (10.6.x), which I have on a separate HD for use with older software that needs Rosetta. I prefer that to running SL server in VM.
-Nick"

Thanks Nick. I've seen some (working) used single CPU 2009 Mac Pros that sold for just a bit more than a new Mac mini. The 2010-12 models however typically have higher prices as of January 2015.
  

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