CPU fan speed has started to vary

[mm]

My CPU fan has started to vary in speed. At least I don't think it
did before.

It's no big deal to take off the fan again and clean it better, but
I'd appreciate your opinions on this anyhow.

It's either 4821 or 4991rpm, no other values.
I'm using ASUS Probe to measure the speed. It shows a wobbly but
basically horizontal line in the graph it gives.

Is this bad?

Okay, after a few hours the speeds have changed to 4891, 4821, and
4787 rpm.

IIRC, it was a straight line, no visible wobbles, until yesterday,
when I removed the fan to get "soot" off of the heak sink prongs.
There was also soot on the fan blades, which I wiped off pretty well,
but maybe I didn't do it completely or evenly where the one blade is
overlapped by another.

It also seems to vibrate when my finger is on it, which I don't
remember happening before.

Is this vibration and speed variation really caused by uneven soot?

Thanks.

(P.S. A) Cleaning the prongs and the aluminum box around part of it
did lower the CPU temp by 15 to 20 degrees, so it's below spec now,
Now it's usually 138 F. I have an 800 MHz cpu; I forget which brand,
on this self-assembled 98/XP computer. I think the fan is 2.25
inches square.

B) The soot came from a badly adjusted oil furnace this past
winter. It also got on tv screens and some on the wall near the heat
output ducts. It's also conceivable that it wasn't badly adjusted but
I closed too many first floor registers (3 or 4 out of 4) and this
interfered with the combustion, at least they tell me that but I don't
see how since the combustion air and the heated circulating air are
supposed to be separate. Yet there is no denying the soot, which is
also supposed to be in the combustion air, not the rest of the house.)

 

[UCLAN]

My CPU fan has started to vary in speed. At least I don't think it
did before.

It's no big deal to take off the fan again and clean it better, but
I'd appreciate your opinions on this anyhow.

It's either 4821 or 4991rpm, no other values.
I'm using ASUS Probe to measure the speed. It shows a wobbly but
basically horizontal line in the graph it gives.

Is this bad?

You're concerned by what amounts to about a 3% reduction in measured
fan speed? I would guess that your PSU +12v varies by that much. Unless
your CPU is showing signs of over heating, I wouldn't fret about it.

 

[GT]

My CPU fan has started to vary in speed. At least I don't think it
did before.

It's no big deal to take off the fan again and clean it better, but
I'd appreciate your opinions on this anyhow.

It's either 4821 or 4991rpm, no other values.
I'm using ASUS Probe to measure the speed. It shows a wobbly but
basically horizontal line in the graph it gives.

Is this bad?

Okay, after a few hours the speeds have changed to 4891, 4821, and
4787 rpm.

IIRC, it was a straight line, no visible wobbles, until yesterday,
when I removed the fan to get "soot" off of the heak sink prongs.
There was also soot on the fan blades, which I wiped off pretty well,
but maybe I didn't do it completely or evenly where the one blade is
overlapped by another.

It also seems to vibrate when my finger is on it, which I don't
remember happening before.

Is this vibration and speed variation really caused by uneven soot?

Thanks.

(P.S. A) Cleaning the prongs and the aluminum box around part of it
did lower the CPU temp by 15 to 20 degrees, so it's below spec now,
Now it's usually 138 F. I have an 800 MHz cpu; I forget which brand,
on this self-assembled 98/XP computer. I think the fan is 2.25
inches square.

I would agree with Kony - the wobble in the line is probably just something
you didn't notice before. However, if blowing out the dust reduced your CPU
temperature by 15-20c, then it must have been very dirty, so perhaps the fan
has a little dirt inside and needs another clear out. Perhaps a little dust
has blown into the fan rotor and it will fail soon, but even it if does then
its not a big deal - fans are easy to replace. even if you can't get one the
correct size, you can mount a larger one with a plastic (or cardboard) duct.

 

[mm]

Thanks to you, GT, and UCLAN and Kony. I've been monitoring temps
and fan speeds closely and will continue to do so, and it's okay.
Plus the Asus Probe goes the front and beeps if any of the two
meausred temps, one measured fan speed, or 4 measured voltages gets
out of range.

Best of all, the variation in fan speed on the diminished after 2 or 3
days and tonight it diminished again and the line is flat at 4856 or
4787**, but there is no visible change to the line!

**I presume the variation doesn't really exist but it appears to for
the reason Kony gave.

Asus-Probe will also keep a history of these measurements, displayed
in graphical form, but I didn't start that right away and for what I
have the time is compressed so it probably would look flat no matter
what.

But I may do the other things suggested anyhow, depending on what
happens with another partially assembled computer.

thanks a lot.