Mac Mini 2011 extremely hot and surprisingly slow I just bought a Mac Mini (mid 2011) secondhand with the following specifications:


2,3 GHz Intel Core i5
8 GB 1067 MHz DDR3
512 GB SSD
Intel HD Graphics 3000 512 MB


I used to have a iMac 2006 earlier, and to my surprise the Mini 2011 seems to be much, much slower. Notice the following observations:


Playing mp4 movies in both QuickTime, VLC and in webpages in Safari works fine for some time, but after a while starts lagging.
The machine gets extremely hot, at most CPU temperature 101 degrees according to my temperature utility. The iMac (and previous Minis) never got anywhere near as hot.
Indicated CPU usage in Activity Monitor seems to increase proportionately with CPU temperature (and how long the machine has been on), but this is somewhat unsure.
The process VTDecoderXPCService sometimes takes several hundred percent while playing video. But sometimes it takes nothing at all.
Encoding PAL videos to mp4 with ffmpeg goes extremely slow (around 1 second of footage per second, while for comparison my MacBook Air 2014 manages 5 seconds per second)


Apple said "80% of the times doing a full format and reinstall solves problems like this". The guy who sold me the thing said he already reinstalled it, but he may not have done a full format first.

Before I go through the trouble of formatting and reinstalling, does anyone have experiences and tips to share of similar situations?

Questions:


Is the Mini actually designed for and supposed to get so warm (100 degrees celsius)?
Is the problem simply due to the CPU being a i5? Are i5's ridiculously much slower than i7's?
Is a full and reinstall likely to fix the problem?
Are there other causes and solutions I should fix? (Save hardware problems and repairs)


Notice that VLC is set to use hardware acceleration and QuickTime runs accelerated by default as far as I know, so the problem is probably not related to this.
The Core i5 processor will throttle it's speed if it gets over what Intel refers to as the 'TJ Max' which is somewhere around 90C. If your software is telling you that you're hitting 100C, then you've obviously got a cooling issue.

Unless you suspect the previous owner tried replacing the CPU or heatsink (unlikely), it might just be that the vents are clogged or the fan is clogged or not working. Fortunately, this should be easy to get to the fan as per the iFixit guide here. You can probably confirm the fan performance by putting your hand over the vent in the back when it is running hot and see if it is blowing a lot of hot air on you; I imagine you'd barely feel anything when you should feel something relatively significant (think: it should blow/flap a piece of paper you hold over it like if you used your mouth to blow air onto it).

Before buying a new fan, you could try seeing if the fan spins easily with your finger (and keeps rotating for a short moment). What I've found in the past is that these little fans can get dust either built up on the fins (easy to clean) or the bearing and/or rotation points could have dust buildup that is causing the fan to be difficult to rotate. What you need to do is clean out the dust (perhaps with some tweezers) and see if you can make it spin with more ease again. Further that, if you are comfortable enough with somewhat disassembling the fan and could get some oil into the fan's bearing, that might make it as good as new. Typical good oil for this is along the lines of "sewing machine oil" or perhaps if you have a RC Car shop nearby, they have nice oils with needle applicators that works great. Reinstall fan and things should be good.

As far as the performance degredations you're seeing and the higher CPU usage, that is certainly inline with the throttled i5 speed; if the chip is running slower, it isn't getting tasks done as fast which means these tasks are taking more of the CPU time (if you look at it as a measurement of time, not capacity).

Hope this works for you!