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Alternator going, or just cold out?

S

searchingforXJ

NAXJA Forum User
Location
Canada
So for the last couple of days I've been noticing that until the engine is good and warmed up the alternator output will drop to around 11V when I come to a stop (idling at a stop light etc). Eventually it stops dropping down and keeps a constant 14V. I've also noticed a little bit of squealing from the belt. I've been meaning to go borrow one of those tension measuring devices from the local parts store. Lately it's been between +5 to -8 F.

Where should I start?
 
I think you already know where to start by your post, with serpentine belt tension. Especially with the related symptom of a belt squeal. Always simple stuff first.

Perform a thorough inspection of the belt (look for ply separation and shiny streaks; called glazing) while you're at it and if the belt is old, just replace it. I have by far had the best luck with Goodyear Gatorback belts. Avoid the el-cheapo belts, you do get what you pay for with belts.

Once you are sure that the belt is sufficiently tight (and they need to be pretty darn tight on the Jeep 4.0) then see if your alternator output stabilizes.
 
I had a similar problem, I needed a new belt. Since then no squeal and gauge shows correct. It sounds like you know where to start any way.
 
x4 on the belt
 
Blaine B. said:
The voltmeter in the gauge cluster isn't also the most accurate, go ahead and double check at the battery with a volt meter.
Click to expand...

I also notice that the fan speed drops and the lights dim when the gauge drops so I'm pretty sure it's reading accurate. I will check it just the same though.
 
This little fella

JeepBeltTool.jpg


http://napaonline.com/MasterPages/N...PartNumber=KR2&Description=Belt+Tension+Gauge
 
Other than the belt problem you may also want to take into consideration depending on what year you have, that the XJ's came with some crappy charging systems, wires etc. With it being so cold as of late, running heat full blast my stereo turned up and headlights on mine drops to around 9volts.
 
I highly doubt 9 volts...

Warm summer day using an OEM 90 amp alternator with stock idle (no extended idle wired YET), AC and HVAC blower on full blast, headlights and foglights on, and all 3 electric fans and I was at about 11.8 volts. Used a digital multimeter.

I do need to get a higher amp alternator. Going to look at ZJ's with the 136 amp alternator. A nice 46 amp increase would be tasty. Also going to wire up an extended idle switch eventually when I get around to it!
 
Blaine B. said:
I highly doubt 9 volts...

Warm summer day using an OEM 90 amp alternator with stock idle (no extended idle wired YET), AC and HVAC blower on full blast, headlights and foglights on, and all 3 electric fans and I was at about 11.8 volts. Used a digital multimeter.

I do need to get a higher amp alternator. Going to look at ZJ's with the 136 amp alternator. A nice 46 amp increase would be tasty. Also going to wire up an extended idle switch eventually when I get around to it!
Click to expand...

Edit: I drop to almost 9 volts. I run two twelve inch subs and when I have everthing running it is just hitting the red on the guage.
 
Last edited:
Have you verified with an external meter or are you just relying on the gauge on the dash?

Like I said that isn't the most accurate....the most accurate would be a digital meter, although another good quality analog meter would be alright too.
 
Blaine B. said:
Have you verified with an external meter or are you just relying on the gauge on the dash?

Like I said that isn't the most accurate....the most accurate would be a digital meter, although another good quality analog meter would be alright too.
Click to expand...

I have not as of yet. Either way I am planning on getting a wiring upgrade kit from 5-90 here soon.
 
The 136 amp alternators that will work were also used in some heavy duty Dodge vans. An upgrade would be nice. 90 amps is whimpy! Especially for as many lights and fans as I have.
 
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