Hot MBP and fan speeds - what are optimal values?

Question

My MBP (late 2006 17" version) seems to be running hot in the afternoons, even though I have air-conditioning on.
I just ran Fan Control (very nice by the way!) and saw the temperature was up around 70 C and the left and right fan speeds were about 2000 rpm.
http://www.conscius.de/~eidac/software/smcfancontrol2/index.html
I selected the "Higher RPM" setting, which sets the minimum speeds to 4000 rpm. After changing the setting, the two fan speeds were initially showing 4525 and 4531.
After about 10 minutes my temperature dropped to 57-59 C and the rpms for both fans went down to about 4000 rpm. And my MBP is obviously cooler to the touch. So I guess the app works.
My questions are:
(1) What are good, safe temperatures for the MBP?
(2) If the temperature was so high, why wouldn't the MBP automatically increase the fan speed beyond the 2000 level automatically? Is 70 C not considered high enough to make the fan run quicker?
(3) How fast is it safe to run the fans at? I am guessing they will die sooner if run faster?
(4) Is making the fans run as fast as possible to first cool off the machine and then reducing the fan speed a good idea?
(5) When it is cold, do the fans stop entirely?
I have actually never heard my MBP fans at all. I guess they are either quiet or my room is so noisy it drowns out the fan noise.
Thanks!
doug

Answer 1

I agree on tjk answer . To add my 2 cents:
(2) : what is not said is that GPU shut down also the computer, but we didn't know at which temperature. It seem anyway that GPU is not designed to run at 90/100 ° C.
at least, not the ati radeon x1600..
Apple seem to consider that 70° is ok, but it could be also the autonomy factor which have been in mind, not the durability of your product.
(3) the fans are brushless. so they are designed to run for very long time at high speed. But they run also with a little lubricant on they rotor axe. with time, this lubricant goes away, and the fan make noise as the axe touch more the outside. a noisy fan is coming from this.
My Mbp was dying and becoming useless, because of fans making really big noise, and even stoping, which is synonimous of death if you don't shut up immediately the computer.
oil on axe have cured them, for now. I can't say how long they will go, but i can play some game, or encode for 8 hours, with fans set up at 4500/5000° in smcfancontrol.
Imo, I will try to set up fans for the macbook to not goes above 65 ° when heavily charged, and 55/57 ° when just surfing.
So it say that I change the setting before I use some soft who need high cpu or gpu power.
and when normal mode, safari only for instance, i have my own default setting at 2000 and my mbp is between 55 to 57°
(my 15' mbp rev A has 1000 rpm by default, so, when doing nothing, it is at 63/65 °)
needless to say that i didn't have any of the bugs I had since I do my manual adjust of fan's rpm. (hard reboot, glitches when playing games, computer freezing suddenly, horizontal lines while playing youtube or movies, etc..)
(4) a better idea should be to ancipate the higher temperature, it is what i do.
cooling fast a piece of computer is not a so good thing . as for anything (a car motor is the same..)
so, before running a heavy game as cod4 or a crossover game, or encoding, if you start your higher rpm just before, you whole computer will not have to go up and down.
that the same idea for letting him at 55 and not 65 . Have in mind that all composants are at the temperature, including your battery (which should be at a 30/40 ° , if we follow Apple recommendations, lol) .
(5) no, they never stop, if they stop, your mbp burn it's intel CPU, you know.... depending on models, it is 1000, 1500 or 2000 rpm by default.
so, a small digest of my post:
cool down your mac, it will always be good for him .
no need to have it at 40°, but try to have 8 to 10° less than now, in all situation.
a fan is designed to run for a long time, not so as well as a hard disk, who can spin at 7200 or more for years, but it is designed to run for years.
as fans are not the same on your computer than on mine, i can't give you the info, but mine have a red zone from 5000 rpm to 6000 rpm, which mean they run at their limits. it's an electrical limit, more than a rpm limit.
A MBP cost a lot, fans don't cost much if you buy them in direct to china, or even if you bought them with apple, or if you just put some oil when they get noisy, as in your car, lol..
if the cpu can run to 100 °, is that the case for others electronics components ?
more than 100 peoples on that forum have a ati x1600 gpu dying..
So my only regret is to NOT have been aware to cool better my mbp 2 years ago, because now, the damage are here, and irreversible.