Volts reading w/cooling fan and loads on?

[btsclan]

I am trying to figure out why my 3G and electric fan instal is draining my electric system so, what does your volts read while the fan is on, head lights and radio etc on aswell when the car is at idle.

I had my alternator tested at idle and it was just over 13 volts but there has been times when I am driving and come to a stop and my volts drop down to around 12.5 volts then climb up again,

My car has an AOD tranny, sometimes when the car is in neutral the volts read higher then when its in gear. I would say on average my volts ride around 13 to 13.5.

Is that normal???

 

[jrichker]

Do you have a 4 gauge power feed wire ?

Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & alternator

Picture courtesy timewarped1972

 

[Darkwriter77]

From what I've experienced with a 3G and electric fan, 12.5 isn't BAD, per se, but it's a bit low for what it should be running with a 3G (should be more like 13 volts). When you swapped on the 3G alt, did you leave the bigger pulley on there that came with it, or did you swap on your old 2G pulley (or one of a similar diameter)? That will affect your charge ability significantly, especially at idle.

Also, as mentioned above, make sure you're running a properly-sized power AND ground wire (replace that useless cheap-o braided metal strap from the back to the firewall with a real 4-gauge cable, and sand/clean your connection points thoroughly). Lots of folks make the mistake of throwing on a big lead wire while neglecting the ground, which can not only affect your alternator's output ability but also can lead to electrical fires.

 

[btsclan]

Yeah I added a 4 gauge ground wire, but probably not in the right spot I think. I have it running from the passenger fender wall to a random bolt under the alternator that I think attaches to the passenger side head.

Should I just replace the old braided wire on the back of the engine to just make sure its grounded well?

Also about the pulley size, I used the pulley that came with the alternator, which is better, using the old 2g pulley or keeping the one that comes on the 3g? Is one bigger then the other? I have heard that changing the size of the pulley you can get more juice out of it.

Thanks for you help!

 

[Darkwriter77]

Yeah I added a 4 gauge ground wire, but probably not in the right spot I think. I have it running from the passenger fender wall to a random bolt under the alternator that I think attaches to the passenger side head.

Should I just replace the old braided wire on the back of the engine to just make sure its grounded well?

Also about the pulley size, I used the pulley that came with the alternator, which is better, using the old 2g pulley or keeping the one that comes on the 3g? Is one bigger then the other? I have heard that changing the size of the pulley you can get more juice out of it.

Thanks for you help!

Yes, get rid of that braided wire and throw a 4-gauge cable back there. You can never have too many grounds on these things.

The pulley on the 2G is smaller than what usually comes on the 3G because the engines they're made for apparently spin the alternator at a different speed due to differences in their belt setups and other pulley sizes. As such, the larger pulley on the 3G will work fine on its stock setup, but when you go putting that same 3G alt on a Fox Mustang with that bigger pulley, it won't spin as fast and, thus, won't put out as much of a charge, especially at idle.

The easiest way to remedy the issue is if you can get hold of a thin enough washer to put behind your 2G pulley to keep it from contacting the alternator's casing when the nut and lock washer are snugged down - DO NOT simply get rid of the lock washer on the outside to make room for a washer, you may wind up losing your pulley later while you're driving. Alternatively, you can either hunt the boneyards for an alternator with a pulley of a similar size with enough of a ... well, I guess you would call it "backspacing" on the pulley, or if you're in good with one or more of the dudes of the local parts stores, see if they'll let you dig through their core return bin for an alternator with a suitable pulley. If all else fails, you can always buy a new pulley off eBay or some other places, but it'll cost ya' somewhere around $40 ... or more, if you opt to buy a full underdrive or overdrive pulley set.