2008 Mac Pro—Fan issues, or more ?

Here's a quick screenshot of the typical kind of run-ups I'm getting on the fans. Instead of the "normal":

PSU: 600 rpm

Exhaust: 600 rpm

CPU: 500 rpm

IO: 800 rpm

...it's more like 1,000+ on the Exhaust, 1,800+ on the IO/Expansion. The other two are normal.

You can see that this is basically at boot up, < 1-minute of uptime.

Any ideas?

Thanks for the input, Grant!

To me, option #1, Dust Bunnies seems like a highly likely culprit.

The temp sensor cable seems tight and snug. The Northbridge heatsink is solid too. CPU temps are pretty normal so that doesn't seem like the heat transfer compound to me.

I cracked it open this weekend and there is a fair amount of dust around the CPU heatsinks. My "canned air" just ran out so I wasn't able to thoroughly clean it all out. But I'd love for the issue to simply be coming from the need for a thorough cleaning.

Thanks again. I'll keep you posted. 😉

Hi Ken,

Thanks for the suggestion. However, as mentioned in the next to last paragrah in my original post—and—just tested again now... SMC resets tend do nothing to stop these 2 fans from continuing to ramp up. I appreciate the recommendation though.

I'm considering a very strong blower. I haven't had that much success with "canned air". They get cold and lose their power and/or start kicking out icey air. But ultimately they just don't have the power I'm after.

I might be purchasing one of these, very soon!

...my Exhaust fan is currently running at 1015 rpm and the IO fan is heading north of 1800 rpm as I type. I have to figure something out. I'm *hoping* it's dust bunnies and a strong blower will fix this issue.

So, I went all out and bought a $60 blower. It's like canned air on steroids. A little loud, but man does this thing move the air.

I was really hoping that this low-tech solution to a high-tech problem was going to be the solution. Didn't seem to. I blew this thing out hard, for a while. I took the ram out, front fan assembly and video card were removed. I certainly dislodged a couple of decent size dust bunnies.

However, within 10 minutes of boot up those same two fans were rising straight back up into the high rpm's again. Shoot! I'm not sure what else to try other than a service visit to the local Mac store. I'm not looking forward to that as those folks are pedantic, condescending and over-priced!

I hope there's some better news to report in the near future, but I'm not holding my breath too much more at this point. Thanks for the suggestions. I'm not giving up, but I'm not sure how much more hope I've got.

Yes, they all have those larger heatsinks on them. I'm away from home now, at my office, but I'm pretty sure that the top riser is the stock RAM (2GB) and the bottom riser is OWC RAM (4GB).

I've run memtest many times (and the 'extended' Apple Hardware test again very recently) and the memory always reports back as okay. Although I've been a little skeptical of the stock RAM. It may be fine, but I've noticed that its heatsink have this slightly oily looking discharge atop the heat sinks. I couldn't figure out what this could be. I was thinking maybe it's thermal paste that was trying to evaporate, or something, but was somehow getting discharged onto the tops of the heatsinks. I don't know... not sure what that would be. Not sure if it's even relevant. But the OWC RAM doesn't exhibit that same "stuff" on the top of its heatsinks.

I was thinking of going back to just 4GB RAM, the OWC stuff, and removing the Apple RAM. Just to see if that altered anything with these fan speeds.

Thanks again for continuing to hang out here. 😉

Too, are there any other iStat readings that I may be able share that would help?

So, I was wrong, as it turned out that upper RAM riser was holding the OWC RAM. This was the hotter RAM. I swapped their positions, Riser 1 for Riser 2: same thing. OWC RAM is consistently about 10° (F) than the stock Apple RAM. FWIW...

As per normal though, after the riser swap, the machine ran predictably unpredictably. I was on for about an hour and a half. No fans ramping. Par for the course at this point.

Hi hatter,

Thanks for the input! I'm not certain that I'm interested in putting too much more money into this system though. For a while I was considering another 8GB Ram and a GTX 285 (one of the cheapest cards to run DaVinci Resolve.) But it's getter harder to rationalize additional expenditures on this box.

This isn't my only machine. Truthfully, it's become a glorified hard-drive enclosure at this point. See, I have a 2012 MacBook Pro with 16GB of RAM and a Samsung 840 256GB SSD. (This SSD is in the optical bay, so I still have the original 750GB platter drive inside too.) This laptop pretty handily trumps my Mac Pro 3,1 in about every task that I can think of. All I really need is access to the drives inside the Mac Pro.

In it's most simple form I've come to see computers as a Brain (processing) and a Bucket (storage). The Mac Pro's brain is growing less useful to me. When it works, it's great. But the fan-ramping is annoying! All I really need is access to it's bucket(s). Instead of dropping, even a small amount of cash, into the Mac Pro I'm thinking I may be better served by investing in a solid NAS to essentially take over the tasks that my tower is doing currenlty. For $800 I could get an enclosure, pull the Mac Pros current drives, slide them right in and get back to work. (Without having to listen to fans ramp up unpredictably.)

This is a 'Plan B' as all I really want is for this Mac Pro to carry on for a few more years. However, the extra noise is pushing me ever closer to warming the ol' credit card. The most aggravating bit is the unpredictable nature of it all. I just wish it would work (quietly) all the time—or present some sure-fire symptoms of a real problem that I could confidently address. Now it's all question marks and shoulder shrugging. Which is aggravating!

Anyway, thank again for your time and thoughts. It's great to get other people's opinions on these matters.

So the death knell has pretty much rung for this machine, unfortunately... I guess, in retrospect, it's really *been* ringing for a long time now. It's been functioning on borrowed time for nearly a year.

Now it won't really boot. It will start, maybe get to a chime, maybe not, then click—turns off.

But I have one final question. There's a red light that stays on, on the motherboard. It's not near the RAM risers, it's closer to the top. It's under HD bay #1, right by the Bluetooth, wireless cards. I've looked all over the web to find out what this red light actually means. (I'm sure it's nothing good!)

Couple years ago, this guy on the Mac Rumors forums, was talking about the same red light and pretty much surmised that it has something to do with the electrical system, and, it's not a good sign.

Any ideas exactly what this light signifies?