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Have an old B&W G3 desktop Mac… noticed an odor yesterday after starting… one of the two small 40cm fans cooling the heat sink is not working… it’s a 5v/0.55W fan… looking at the eBay options, there is a 5v/0.6W fan by same manufacturer … much lower cost than the OEM unit… are the specs that critical? Appreciate any input as to replacement. Thanks
Earlier Mac models
A pair of heatsink-mounted processor cooling fans in a B&W G3 isn't Apple OEM hardware, so it must have been a user upgrade, possibly a faster G3 or G4. If it's a 5-volt fan and the same 40mm size, the RPM is likely the same, since those fans were used for the same applications. The negligible difference in wattage draw isn't a concern. When installing, just be sure to install it so that the flow of air is up, away from the processor. That way it will be exhausted in the direction of the case's large cooling fan. Since one fan has gone bad, I'd be inclined to replace both, since they've had the same number of hours of operation and aren't expensive.
Here is a picture of a stock B&W G3 opened up. One large case fan exhausts out the back, and there is another fan on the back exhausting air from the power supply. Outside air is drawn into the vents on the front, and hot air is pushed out the vents on the back.
Not sure where those little fans you are talking about are installed.
https://www.cultofmac.com/wp-content/uploads/2017/01/powerMac_G3_print_spread.jpg
One thing to check when you open it up, is the thermal paste on the CPU to heatsink contact point. If that has dried up or does not have good thermal contact, then it won't really matter what the fans are doing, the CPU will just overheat anyway. A small dab is all you need, but you might need to clean the old paste off first. Look up some videos on how to do that. That will ensure that the heat sink is actually doing its job in the first place.
Cooling fans for G3 CPU heat sink
