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yertleturtle

macrumors newbie
Original poster
Oct 20, 2014
2
0
I just upgraded my ram on my mac pro 3,1 (2008) and the fan is now running at 2500 RPM even though the temp is only 27 C. Two chips of the old memory (Riser A/Dimm 1 and 2) don't show a serial number. Everything else looks correct to my eyes. Any help is appreciated.

Included is a screenshot of my System Info.
 

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I'm guessing you bought FB-DIMMs that don't have a temperature sensor. At least one other person has reported the same problem (high fan speeds) for that reason.

Basically, in order to be quiet, the MP uses just enough fan speed to keep things cool. If there is no temperature sensor, it doesn't know how hot the RAM is, so it runs the fans at maximum and/or slows the RAM down.

From the 2008 MP manual:
Apple recommends that you use Apple-approved FB-DIMMs. Other FB-DIMMs may cause your Mac Pro to operate louder

From Apple (Technical Note 2156):
The Mac Pro will run the fans at full speed when detecting FB-DIMM's without a functional temperature sensor, which will maximize cooling on the FB-DIMM's. While the full speed of the fans maximizes the preservation of thermal integrity, FB-DIMMs with inadequate heat sinking may still overheat depending on ambient temperature and system load. In this case, the Mac Pro may shut down the system to protect the FB-DIMM from possible thermal damage.

I would look up the model number of your memory sticks to see if the specs state whether or not they have a temperature sensor. A lot of RAM sticks, even ECC server RAM, don't have the sensor.
 
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