The 3G has a cleaner look and better cooling with an internal fan.
The 2G is prone to connector failure resulting in possible fire hazard. See TSB 96214.
the only downside is that if it fails, you just cant go to the parts store & tell them you want an alternator for a '92 Mustang GT. You'll get a 2G. Make sure to write down all of the part numbers and applications for all of the non-stock parts....makes things much easier when the time comes to replace it!
75 amp stock alternator 130-200 amp 3G .. No electric fan without the 3G or anything else for that matter..stock alternator is too small to begin with..
Electric fan = 3G alternator if you want long life & reliability from your car.
The electric fan saves some HP. The stock fan's parasitic drag runs from 7-12 HP depending on who you talk to. The electric fan uses about 1/2 HP of power from the electrical system.
Figure this:
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps
That's grand total of 74 amps from a 65 amp alternator. Talk about overdrawn at the bank!
I found that on my 2.3, the stock alternator was JUST adequate. IE meaning with the A/C on full, heater fan blowing on high, cooling fan running, headlights on high, and cruising 75 mph, the voltage at the battery was 12.9. Hit the brakes (brake lights) and it would drop to 12.7-12.8 which was exactly the voltage with the engine not running at all.
Swapped in a F-150 3G style alternator (not sure of the amperage) and voltage at IDLE (800 RPM) with EVERYTHING on (A/C, HVAC fan on high, tail lights, high beams, brake lights, radio on, interior lights on, etc) is 13.6V. Doesn't help MPG or HP, but it's quite a bit more confidence inspiring especially since I drive in the dark about 75% of the time....and of that 75%, it's almost ALL between midnight and 4am. Not a good time to have a alternator fail!
Hmm. I ran an electric fan, a sub/amp and a 190lph fuel pump off of my stock alternator on my coupe and never had a minutes trouble. Maybe it was alot to ask of the stocker but it never failed me in four years.