So over the last few months I've noticed my voltage drops (monitored with Ultra gauge) while I'm at a stop light. It is especially noticeable when I have my lights on and the heater on full blast. It's actually been doing this for a couple years now but it would only drop from 14.1 to like 13.5v and I figured it was no big deal.

The second I start to drive again, or if I rev up the engine, the voltage goes back up around 14v.

I've seen it dip down to as low as 11.5v while I was waiting in a drive thru.

Alternator is original (Denso) so 223k miles on it

Battery is a Costco/Interstate about 3.5 years old.

Belt appears to be as tight as it should be.

I do have another OEM Alternator but it has about 200k on it. I was thinking I would rebuild my spare alternator (new brushes) and swap it in.

Does this sound like a alternator starting to go bad? If so, should I just replaces the brushes on the spare alternator I have or are there other things I should replace on it.

Thoughts?

that sounds pretty reasonable to me. I can't see a reason to replace it based on what your saying. these alternators are considered temperature compensating charging systems so maybe keep that in mind when looking at the numbers coming out?

also maybe make sure all the contacts are really nice and clean. I noticed a big difference once I went and wire brushed everything. I was seeing lower number like 12.2 at idle and then once I cleaned everything up back right up 13.7 to 14.0 sometimes.



I don't know if money is a huge issue for you but... when it comes to stuff like this I would say for $190 just get a reman from denso direct. I used to re-build everything but for the prices now days it's just easier for me to grab a reman.

DENSOProducts

I have a good 70a and a good 80a Alt. Both have new brushes in them and the 70a has a new regulator and rectifier and both only put out around 41-45a in gear at 600rpm.

To me it’s a Denso Alt thing. They only regulate to 13.8v. As long as your battery light isn’t coming on your Alt is pushing as much as it can at idle in gear with your foot on the brake.

You are seeing what I’ve seen for a few years since I started watching system voltage.

To me, if you want 80a output at idle it’s time for a bigger or better alternator.


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Does anyone know of a Toyota/Lexus with a higher amp alternator that would bolt in to these? The Sequoia mount is different. I'm not into the idea of installing a GM alternator (crap) that has been rebuilt (possibly more crap).

Not probably. Most of the parts store rebuilt gm alternators I've installed are warrantied out like once a year.

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I have been running this one for the last nine months and it’s been fine. It’s not cheap but when I did my electric fan conversion I needed to provide some extra amp. It’s the same housing as our OEM.

High Output Alternator 160 Amp 1996-2002 4Runner 2000-2004 5VZ Tacoma

Yeah, that's alternator failure alright. That's what happened to mine after I added an e-fan, the stock unit burnt out. You could try replacing the brushes but it's probably toast.

I'd run that other used unit you have laying around as-is. It's a very easy part to replace, just one bolt and nut on the front, one nut off the back and one wire connector and you can wiggle the guy out. Only tricky part is the sliding sleeve in the mount that you have to push/smack back in.

My [what appears to be the] original alt at 170K miles puts out 14.4V at idle on a cold morning (45ºF). Measured with Scangauge 2.
Bought this '97 4R. at 120K miles, now 170K miles, and have never seen voltage dimming at idle vs. revving.

I know your batt is fairly new at 3.5 years. I don't know how hot it gets up in WI, heat shortens the batt life. Having it checked is free at the auto parts stores. Get a free check so you can rule out a sulfated batt as a possible issue. If batt checks good move on to the alt.

When your under hood temps are 120 degrees tell me what you got. I have no issues in the dead of winter also.

I also reiterate that it is at 600rpm in gear with your foot on the brake that it won’t keep up. If one is driving a manual you won’t see this. If your in an automatic and your foot on the brake in gear idle rpm is above 700rpm because of a dirty IAC or vacuum leaks you won’t see this.


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I think when it is the brushes worn, you see intermittent charging/no charging with a corresponding light on the dash. Not sure they could just cause decreased output but they are cheap as chips so why not try?

So I think I'm going to throw a new set of brushes in my spare alternator. It does appear that there are two different types of brush kits based on what year your truck was produced. This is what I've found:

PN - 27370-35060 is for trucks with a production date between 11/1995 - 07/1998.

The part looks like this: https://www.amazon.com/Genuine-Toyot...52&s=hi&sr=8-1

PN - 27370-75060 is for trucks made after 07/1998

The part looks basically identical but doesn't have the plastic shroud around it: 27370-75060 - PartSouq - Auto Parts Around the World

They may be interchangeable, but I cannot be for sure. I'll need to disassemble my spare alternator to be certain which type I need.

Headlights, fogs (8a), fan on speed 2, in gear with Brake depressed.

Same as above but fan on speed 3.

Same as above but fan on speed 4

Same as above with trans in park idling at 700rpm instead of 600rpm. Outside temps were 22f and inlet air temp was 31f.


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Unless the voltage is dropping below ~12.7V, your battery is not discharging. Below 13.3-13.8V or so (depending on temp) your battery is not charging.

The voltage regulator in the alternator is temperature dependent, and will drop (by design) at higher temps to adjust for battery needs.

Cleaning terminals, etc. is a good idea. I don't think your alternator is showing signs that it is dying though.

-Charlie

I’m 99% sure if it was summer that 13.1v would have slowly dropped like before where the Alt was pushing 41 amps into the underhood junction box and 2.5a was coming out of the battery going to the junction box and post voltage was 12.7. My Fluke amp meter is directional.

I also have a Hall-Effect amp meter I can mount permanently if I wanted too. I use it for troubleshooting while driving (currently) because I can install the sensor and run it’s leads into the interior to see what’s going on.


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