pletzvet

The car: '85 auto, no idea how old the alternator is but it is the same one as when I purchased the car 4 years ago and it didn't look new then, battery is 2 years old, well maintained and never been a problem. I just completed a pretty extensive thread search on alternator voltage and read lots.

Here's what happened:
Hot day today 30 degrees C! AC was on and I was stopped at a traffic light; looked down to check the temp display, and the red light was on reading 11.7 or 11.8 volts. (As we know, the display for coolant temp and volts share the same space on the digital dash and when a reading goes out of accepted parameters, i.e. low voltage, that reading/display will override what ever the selected display is.)

I shut the AC off and increased RPM's to about 750 and the volts began to move higher - into the mid 12's. I'm pretty sure that the volts have been reading between 13.8 and 14.3 since I've had the car (4 years). Later, while cruising home for 3 hours (highway driving), with headlights and radio on, even turned the AC on for a half hour - the volt display fluctuated between 13.9 - 14.1, but when idling the volts begin to drop off, sliding downward to 12.6.

I always thought that when an alternator bit the biscuit, it was a pretty sudden event.

This event reminded me that I notice a slight flicker in my digital dash a few days ago, but didn't think much more of it when it didn't continue.

Maybe a regulator? Possibly a ground, but I doubt it.

If I arrange to have the alternator tested - what tests do I specifically ask for, since it will be hard to replicate the heat that was under the hood when this happened.

Comments/suggestions appreciated.

blakngold4life

I just changed mine last week and the symptoms where about the same; lights flickering, radio turned off and on and the volts where at around 11.5. Changed it and everything is fine, volts are around 13.5 now. Its not a difficult thing to change so you may want to change it before you get stranded somewhere.

rsovine

The alternator on my 84 went out on a 3 hour trip. I had noticed for weeks about the flux in the volts but thought it was loose wires and such.

To my dismay, the alternator was dying and it did. About midnight on a road with no cell phone service. The volts started a downward spin and in about 30 minutes the battery and car were dead.

The new alternator, not a rebuilt one, was around $110 US dollars. The tow bill was about $250. So please go get your alternator tested and buy a new one if it is out. The automotive store has a standard test they put the alt on. The test will tell them volts output and amps. 13.8 to 14 volts is normal operating range for the vette.

Good luck and God speed.

pletzvet

Appreciate the responses, blackngold and rsovine - this forum is so useful when comparing similar experiences that others have had - helping us find solutions. I especially appreciate your comments on avoiding getting stranded, 'cause that was exactly what I was thinking about before hitting the highway for a 3 hour drive. Fortunately, it didn't let me down and my wife and I enjoyed the trip - of course, I didn't tell her that I was worried about the alt - what's the use, right?

pletzvet

I'm guessing that my alternator is almost cooked...I'll have it tested when I take it out. Presuming that it is a 108 amp, is there any reason NOT to replace it with a 200 amp, or asked another way...without any mods drawing extra load on the system, should I just replace it with another 108 amp as OEM?

JrRifleCoach

A coupla questions;
1. How often do you drive the car? Once a week?
2. Are you using a battery tender whenever the car is parked?
3. Have you checked the batt term connections and the end points of the main cables?

Unless your running more power needs than stock, theres little reason to move to a larger alt than stock. If you keep a battery tender on the batt whenever its parked, the alt & batt life will be extended to a more average life span.

pletzvet

1. Once or twice a week, mostly short drives, but on this occasion I had driven 3 hours and the car had been driven a couple of other times during the week.

2. Have never had a problem with battery going dead - car has sat for weeks and never been a problem - never felt the need for a batt. tender.

3. I agree - can't hurt to have clean connections, but again - have never had a problem starting or with grounds and the battery was re-installed this spring and the terminals were cleaned then.

I pulled the alternator this afternoon and will take it in for testing tomorrow, but pretty sure it's almost fried.

jfb

Alternators are suspect if they cannot maintain level output voltage. Normally the dash voltmeter will read 14.3 volts engine cold and the output voltage drops to 13.3 volts at operating temperature. Unless you have an unusually heavy current load and a low idle rpm, you shouldn't see the below 13.0 volts you saw. I suspect your alternator is at the end of its life.
Merely replacing a 108 amp alternator with a 200 amp one is ok until you have loads that exceed the fusible link in the output wire of the alternator. 200 amps will blow the fusible link. I doubt your car will ever draw 200 amps and if it ran ok with the original alternator, it still will with a properly working 108 amp one.

Vette Fast

I agree with the above advice. If you are still looking to upgrade try the powermaster 140 amp alternator, sold through Summit racing equipment. If at a later time you should upgrade radio, fans....... you will have the extra amps needed.

JrRifleCoach

I don't know how many times this needs to said; If your not driving your Vette on a daily basis, the battery will loose some of its charge. If your depending upon the alternator to carry the system load and top the battery on each outing, your asking too much and WILL weaken the alternator. And abusing the battery in this fashion will also shorten its life as well. Those that leave their Vette parked for weeks before drives are only making the problem WORSE.

For years I read of members that replace their batt and alt every 12-16 months and are all butt hurt because Auto Zone or Kragens has sold them crap products.

All you guys need to do is buy a battery tender and hook it up each time you park the car. I drive mine on the weekends and it sometimes sits for a coupla weeks before it sees the sun. The battery has lasted four years and the alt is almost six years old.

Its all about maintenance my friends. Maintaining the battery with a battery tender is just like changing oil. If you want your car to be ready for the next ride.......

pletzvet

Appreciate your comments, Coach...I agree that maintaining a battery with a tender is not a bad idea, but...in these circumstances seems to be a little over the top. Sure, if the car sits all winter (serveral months) with the battery in it and no batt. tender one is asking for trouble. I take the battery out when it goes into storage and charge it a few times over the winter. In the summer, the car is being driven regularly, and there has never been a problem with the battery losing charge or going dead. A battery by virtue of its design and purpose should be able to take a little discharge and recharge without shortening it's life - that happens everytime you hit the key to start the car, right? As far as putting undue stress on the alternator in the absence of a battery tender, I can't agree - the alternator is working all the time the car is running to provide power to all systems and this is no different than the alternator working a little to top up the battery - right?

pletzvet

I think I might be wrong in referring to the output at 108 amps, should be 120, nonetheless - your point is well taken...the fusible link probably couldn't hand 200 amps anyway, plus I don't expect to be adding anything to draw that kind of load. OEM is probably just fine.

pletzvet

I was looking at these - nice (and chrome too!)...the only problem for us Canadians is by the time the duty and shipping charges get added in - the price gets kinda crazy. I will check with my local parts guys to see what kind of price they can get on it. Thanks for the suggestion.