The alternator and battery were dying on my 2011 4runner Trail, so replaced them along with a new serpentine belt. I used an Ultima alternator from O’Reilly.

It started right up with no issues. My aftermarket stereo shows vehicle info, including battery voltage, which stayed between 13.1 and 13.3 for several hours of driving.

It started raining VERY HARD and after a while, the voltage would slip down to 12.0 - 12.5 and the dashboard battery light would come on. Within a few seconds it would go back up to the low 13’s.

It seemed to happen most under hard acceleration and on the highway, but was not exclusive to those situations.

As I was finishing up on my truck, it started raining, and it was outside, so I didn’t put any dielectric grease on the battery terminals. I did spray them with electronics cleaner but only let it sit for a few seconds and wiped it off with a shop towel, but they weren’t very dirty and weren’t corroded at all.

There was no belt whine at all the whole time I was driving.

What could cause the voltage to slip down randomly for a few seconds before going back up? It never lasted more than a few seconds, but it’s still concerning to say the least.

Thanks in advance!

Two guesses:

1. Something is loading down the new alternator and it can't keep up.
2. Bad new alternator.

Have the new alternator load tested at the place you bought it.

The plot thickens…
The black plastic cover that goes over a bolt on the alternator appears to be melted. Any thoughts on what might cause this? I attached a pic.

Used my voltmeter and got:
12.5v with car off
Turned it on and read 13.7
Turned on headlights and AC and it dropped to 12.5v and did not go back up.
Turned off headlights and AC and it stayed at 12.5v

Attached Images

 

As one of possibilities: bad connection under that plastic cover (bolt not tight?), bad connection is going to get hot when current flows through it consequently melting that plastic.

And if I am correct and that connection is bad then it also would explain your voltage reading.

This was it, thankfully. The nut apparently broke when I tightened it before and I didn’t notice, so it had a bad connection and must have been arcing, thus melting the plastic cover.

I cleaned everything up with electronic cleaner and put on a different nut. I cleaned up the battery cables for good measure.

New readings:

Battery with truck off: 12.5v
Battery with truck on: 14.1v
Battery with truck and all accessories on: 14.1v
My face: smiling 🙂

Thank you so much for the help, I am so happy I didn’t have to pull the alternator. That’s really not a fun job 😂

How important is that black cover? Do I need to get a new one? Is it safe to drive without it?

I was thinking of just hitting it with some dielectric grease to insulate it.

You can drive without it. It is there to keep shorts from happening, such as if you close the hood too forcefully.

Thanks!

Sure thing!

You can drive without it, but IMHO I would recommend getting a replacement or finding another way to cover it with insulator\plastic cover at some point in the future.

That bolt is connected directly (no fuse or fusible link) to the positive side of the battery, if any grounded conductor touches it (like part of the car in accident\ any metal tool \wrench when you are working on the truck) then more than likely that metal will be instantly welded to that bolt\wire… consequently the process of melting of the wire and your battery will began… and it can lead to fire.

If it was arcing and melted plastic with a bad bolt, it will arc to metal that gets too close... best to not leave it exposed.

New alternators suck, plain and simple. Almost all of them are rebuilt, poorly. Been down this road too many times with customer vehicles. It's tough to find a brand new one, no matter where you shop including the dealer.

Sorry, maybe I'm a little bitter, especially after see this this scenario too many times.

If the vehicle is off, and your battery dies, this is battery or current drain issue. Each time you drain the battery, it loses a little of it's life.

If the vehicle is running, and the battery dies, its almost always a alternator issue or wiring from alternator to battery.

The two are not the same.