New Alternator Gets Hot

[MrSony]

Ok. Bought a new 12si alternator.
This is a napa alternator part number https://www.napaonline.com/en/p/NNE1N4350?impressionRank=1

It doesnt charge at idle, but at say 900-1100rpm it will read 13 volts on the gauge. Fine enough. Overdrive pulley will fix that. But, it gets hotternhell, to the point you'll get 2nd degree burns touching it. 3 hours after I shut my car off the headers were ice cold but the alt was still warm to the touch. I was looking at it, and is the fan mounted for counter clockwise use? Do I need a clockwise fan? The air intake at the back is not blocked, theres about 1.5-2" of space between it and the valve cover. (and yes I swapped the wires around, it was late and I was up for 24 hours at that point).

 

[mikester]

Not sure if it would make a difference but I would use a heavier gauge wire from the output post. Maybe you have a defective alternator. Take it back and get a different one.

 

[olds307 and 403]

I had 94 amp Wilson 12SI reman that would not charge at idle but put out 14+ volts, once revved up. It sounds defective, it should be at least mid 13's if properly charging.

 

[jlcustomz]

It's just a p.o.s. alternator with very poor internals if it doesn't charge at idle with that pulley. A 78 amp alternator should be fair for running fans
I'd also agree with a larger output wire not being a bad idea , as well as checking engine grounds & maybe even adding another. I usually ground a multi-terminal battery to radiator core support also. Grounds likely aren't your real issue, but it's peace of mind to keep em not the issue, now & forever.
I assume you 're talking about some sort of add on electric fans, which do require a decent alternator.
Larger wires & good grounds get maximum efficiency from your alt. A large one under load will get pretty warm & retain heat for a while. Improper wiring & it will get hot. So will your wires.
Few more details there please, single, dual, size, brand , mounting method & location. Fans are best mounted behind radiator (engine side) & pulling air through radiator. You can easily feel if it's blowing the right way towards engine.
On front side pushing is less efficient.
Some universal fans have reversible direction blades, some don't.
There is alot to having proper working electric fans. If you got some large single strap on thing from Napa, it probably won't cut it. Fans also need proper shrouding with radiator. Factory take off twin fans are the best affordable, but definitely are not made to run full time without thermostat control. I know there was discussion here.

 

[MrSony]

My fans are stock 4th gen V8 fans from a 2000 Camaro. Wired to both come on full beans all the time. 30A fuse and a relay. Never popped a fuse

 

[jlcustomz]

I Had no idea what you might have on fans.Got those also. They aren't meant to run full time though.Will wear out & are a strain on a small alternator.

 

[olds307 and 403]

I believe good fans are 50+ amps at start up and maybe high 20's running. You could be pulling the maximum amps being put out. I did have a chrome high output 10 SI that got very hot, it didn't last a long time. Why didn't you get the 94 amp version?

 

[Turbo Zach]

So you didn't have any trouble before and now you do after changing the alternator? Sounds like you have a bad alternator or you wired something wrong. Is it the same altinator as the one before?

 

[g0thiac]

Have the alternator tested, and ask the people working on it if overheating still happens.

Otherwise you got some high resistance going on there that will need addressing quick.

 

[CopperNick]

Right now I have a stack of older three wire alternators on the bench, all of which worked when taken out of service and none of which would kick the needle on the voltage gauge over to 12.5 or higher until the engine rpm exceeded the built in threshold above which they would start to charge. My one wire Tuff Stuff is a 125 or heavier and throws 14.5 volts at around 900-1000 rpm and it won't self initiate below that 900 point. The needle on the gauge will sit in the yellow zone until the rpm's come up and then vroom, off it goes and the needle heads for the other end of the range. According to the tech sheets it is perfectly acceptable behaviour and nothing to worry about. You can actually tell when it kicks off because the engine rpm actually drops under the load and then comes back again.

Heat strong enough to, maybe, cook an egg, on the other hand, is a problem. It being a Napa unit, were it mine, it would be off the engine and back on the counter at the Napa store asap. Most of them no longer have in store ability to test what they sell. If a unit comes back as apparently defective, it gets sent to the distribution center and a warranty card dropped on it. The ones I have kept were pretty much intended to be used as cores but even the rebuilt ones that I sourced had a hard time keeping up with the internal demands they faced. That is why I went big dog and aftermarket. I think the only stocker left in service is the one on my Monte; that I will have to check jic. At least if I need a core, I have one for trade.

One thing kind of tweaks my memory here, is the alternator turning in the right direction? This is not about the ability to charge this is the fan in behind the pulley having vanes in it that pull in air to keep the alternator happy, If that fan has vanes that are not pointing in the direction of rotation or if the alternator is spinning in the wrong direction, well it ought to still charge okay but there won't be any air being pulled into the alternator casing to keep it comfortable.