Hey guys, just wanted to run this past you before I bring it in to the service center. My car is mostly a short-trip daily driver. I drive probably 15-20 miles per day, and everything is peachy. However, on longer highway trips, my battery light will come on after about 30 minutes of driving, and sometimes go out a short while later. This happens on and off the entire time I'm on the highway- never happens on short trips.

So, what I'm thinking is that I have a problem with my alternator. On the highway I'm cruising at relatively low rpms, and maybe not enough current is being generated? I don't have subs or an amp, and this happens regardless of whether my headlights are on or not. Also, I don't have an underdriven pulley... yet.

Anyone have any other ideas of what it may be?

 

I would get one of those Yellow top battery.

 

Check the belt tension and condition of the belt.

 

Just kinda Curious, usually how many miles should we change our belts ?

Im thinking 30K. good enough ?

 

My car is at exactly 30k right now. Checked the belts- they're fine.

 

If the belt is not slipping, the trouble is in the alternator or voltage regulator. I'd suspect a diode that's happy on short trips, but gets flaky when it gets hot on long runs.

Do your lights dim when the alternator light comes on?

When alternator light comes on, is it bright or dim?

If you want to putz with things yourself, see if you can rig a voltmeter so you can check charging system voltage while driving. Then try to make sense of what you see. It's possible for the light to come on but the alternator is still putting out. Voltage will tell you that.

Take it to the dealer, and hope they have a good electrical guy. Actually, they should hope they have a good electrical guy. A good one would identify a bad part and fix the alternator. A mediocre one would just replace everything. At 30K you're under warranty, so it's their money.

BTW - an alternator should put out enough juice at highway cruise. The reason auto makers went to alternators, instead of the old generators, is that an alternator will charge even at idle. Generators needed some rpm to put out charging current.

Ken

 

what color is it. are you sure it is the batt light? sounds more like that pesky rad coolant light.


beers

 

Ken- thanks for all the suggestions. The light is bright red, and it looks like a little battery. My lights don't dim when it comes on- in fact nothing of note happens other than the light coming on. I'm just trying to get an idea of what it could be so they don't just hand it back to me and say "can't replicate problem." I mean, it really does take like half an hour of driving at least to make this happen, so if they don't actually plan on going in with a multimeter or something, chances are I'll be back multiple times... just like the marbles in the blender problem (still not fixed).

 

i thought they were both RED hehe

yeah it prolly is your alt, mine did the same thing when i was on a trip was fine the whole trip parked car, even ended wen to leave light was on, drove a bit nothing stopped revvvved a bit and it went off, drove and started out...turns out the alt was putting out too much and fried itself as well as the battery anyways bad week lots of crap off of that with the dealer, then i finally got it fixed and all is better...so in conclusion this is the short version of the story, GET THE ALT and BATTERY checked ASAP

 

Im 32K going 33K in maybe another 2-3 days

Have you guys heard of this high output Alternator ?

http://www.mechman.com/home.html

I wonder can it handle our 9K RPM.

 

Thanks guys. I don't know where I'd be without all of you. Probably stranded somewhere.

 

Make sure you tell them that, so they can replicate it. Unless this has happened enough that they know what it is.

Warranty item, so you should get a loaner while your 8 is being examined.

Ken

 

appointment made, loaner cx-7 reserved lol. Thanks!

 

Well it's in for service.. the guy said he'd never had to replace an alternator in an RX-8 before, but he'd take a look. While it's in there, do you think I should ask them about my rusted rotor hubs? Is that something warranty takes care of?

*Nevermind- not covered

 

So they weren't able to duplicate the problem, however they tested the battery, and it's bad. Not enough CCA's. So it's being replaced pro-rated under warranty, which means I pay half of the battery's cost ($69). Kindof a bummer since if I'm replacing the battery anyway, I'd prob want to get an optima or something. But whatever, they're doing the labor, and I live in a warm climate, so it's ok.

 

So I figure its better to revive an old thread than to create a new one. I have a sim. sisuation as this one. First my battery light normally comes on after I start the car, but thats not all. If I am cruising down the road at a constant speed for a few miles my battery light will come on again. It will stay on for a minute or so then go off. Is it time to replace my battery?

I have a 2005 with 40k miles, I am not sure if the battery has ever been replaced

 

are you sure it is not your rad coolant light. they look close to the same.. and the coolant sensor is a know problem and does just what you describe..

beers

 

I will go check my manual and see what light I am getting

 

Stock battery is crap. even the "updated" battery is still crap

they replaced my battery back then, and finally after 2 years and 11 months of service, it died. not taking charges.

garbage

Replaced with Red Top Optima. Couldn't be happier.

 

yellow top for the win.. cause i got a stock radio that pumps up the talk radio.

i will say my updated mazda battery failed at the 3 year point. no lights on the dash. one day it was fine. the next day i had to jump my car with my motorcycle. it was fine for a week. then, bammmmm. done..

beers

 

Im ok with stock setup. Bose aint that good in this car. but I enjoy music at home, not when Im driving (cuz I enjoy driving when driving lol)

thats about the same as me. The day b4 it was fine. then one morning, it cranked slow as hell. it did work, after another few days. Barely turned over. then it just died.

 

really i was serious.. i have the stock radio also.. i think music should be enjoyed live..

but i guess the point i have been making is if the battery is going you dont get a light for it..

bad alt or broken alt belt yes. failing battery no..

beers

 

true true ...

I can install a volt meter to my battery but hmm ... I have free 3 yr replacements on my red top ... so if it dies in 3 years. I get a new one for free. then 72 months pro rate ..

Its easy to kill a battery anyway ... hehehe ... after 2 years and 11 months ... crank crank crank crank crank till it die ... LOL ! Another new battery