I have a couple old Mac Pros sitting in the corner of my work office crunching numbers, and rendering randomly. Their CPU’s are always at 100%. I’ve had them apart half a dozen times to do upgrades, and I’ve never been very happy with the CPU temps. I’ve traditionally used Arctic Silver 5 (AS5) since it’s what I have a large tube of, and generally like. But, as I said, I’ve never liked the temp the Mac Pros run at, and because they’re at 100% all the time, the AS5 never has a real chance to “break in” (which requires many many hours of several thermal cycles). So, last week, I bought a tube of Arctic MX-4 (to be clear, Arctic Cooling (MX-4) is not the same company as Arctic Silver (AS5). The biggest advantage of the MX-4 being it has no break-in period.

Because the Mac Pros have Xeon 5300’s in them, I used the instructions on the Arctic Silver site for a “Horizontal Line“. After tinting the heat sink and heat spreader, I applied the compound and remounted the heat sinks. On power up, and after the machine had a chance to warm up, I am getting 42C and 44C on the two heat sinks at 100% load after 24 hours. On the Mac Pro I haven’t re-done yet, by contrast, I’m getting 44C and 50C. Mind you, those numbers are on a machine that I’ve never put a lot of effort into “breaking in”.

Of interest, I did notice that some of the AS5 on the machine I did looked like it had “broken down”. It was brownish, and had slumped quite a bit. Could be the AS5 I have is too old, or that because it never got a break-in period, it never settled into position, I really don’t know, but it was pretty gross to clean off the CPU heat spreader.

So, I’m happy, and hopefully those numbers will continue to hold. I will be re-doing the second Mac Pro next week. We’ll have to see if the same numbers show on that machine. Will definitely post those results as an update.