In the past always ran a steady 14.1 - 14.2. volts. Recently I had to replace the alternator and put in new battery. Now volts drop down as low as 13.4 and up to 14.3 back and forth at different times. The drop is mostly during idle and then climbs to 13.8 stays for a while then eventually goes up to 14.1. I am concerned with this because I never experienced any variance in the past. Any thoughts on why it is happenning now right after the new parts? Thanks Dave.

 

First thing I would do is check the quality of connections, you must take them apart to check. Remove the bolts competelty from the battery cables, they come right out with pliers.

Does the voltage jump up and down or is this a very gradual thing?

Where did you get the new alternator?

Have you checked with a volt meter?

Pete

 

Pete, Actually this is the second alternator and battery. The connectors are clean and have no movement at all. The voltage change is gradual.

 

Well, it's normal for the voltage to be higher when you first start the car and gradually come down as it warms up. It is also normal for it to drop lower at idle than at cruise speed. All the voltages you list are OK, and gradual changes are OK. If you leave the car sit for periods of time it's a good idea to keep an auto battery charger of some sort to keep the battery topped up.

If your idle is too low, the voltage will drop off - also if you have underdrive pulleys. Your problem does not sound super concerning, but depends when and why it is happening. Sorry, I'm not comming up with much for you, anything else you can add? Any high amperage devices such a big stereo or something?

 

Lots of us seem to go through one alternator a year. The engine compartment heat wears on them. I've got a pep-boys special with the lifetime warranty. :D Dies, walk in, get a new one, no question.

 

Thanks for the thoughts. There are no new big draw add on's the only recent issue was when I blew the "guage" fuse when hardwiring a radar detector the other day. Is it just a coincidence the reading changes started the next day?? Or could have the short effected something else? I'm mainly concerned because the readings are different from what I was use to seeing in the past.

 

my old 86 just drove me nuts with the same problem, but it would drop to just below 13 and up to almost 15. called the old factory corvette hotline they used to have and they convinced me that as long as it showed around 12.9 at idle everything was okay. i still had a local favorite delco shop rebuild an alternator for me and put in a fresh delco battery, but once the gauge started moving around it never stopped. they finally got tired of me complaining and pointed out that the battery was charging and everything was fine. i'd keep an eye on the state of your battery and if it keeps it's charge then just enjoy your vette, of course if the battery starts getting weak it will kill your starter.
good luck
david
99 pewter coupe 6 spd
94 dark red coupe 6 spd (for sale)
86 dark red coupe (dead)

 

Thanks , David.

 

What you observe is normal. When you first start your car, the alternator charges with high current to replace the energy taken to operate the starter motor and when the engine is idling, the alternator isn't turning fast enough to put out its rated current. If you race the engine slightly after starting you will notice the voltage will come up to 14.3-14.7 volts. This will be the reading when you are underway, however, when the alternator get warmed up, its output voltage falls to about 13.3-13.8 volts because the voltage regulator in the alternator doesn't have good temperature compensation. As long as the battery has more than about 12.6 volts across it, then it is being charged and you do not need to worry. Also, with a lot of electrical eqt on and idling , the alternator may not be able to keep up with the load and the voltage will fall, but unless you are going to idle for hours, don't be concerned because when you get under way the alternator will be able to supply the load current and replace what was lost during the stoplight sit. If you see the battery symbol light up on your dash, your alternator isn't working at all and you should turn off everything you can and head for home .

 

What you are experiencing is normal and will subside a little over time. A quick question. How is the alternator belt? If it is slightly worn, it will slip somewhat. Change the belt as well. Once done you will be suprised at the difference in the voltage variation change (or reduction of it).

 

Thanks for the assurances JFB, what you explained is exactly what I'm experiencing.

Bob, I'll also replace the serp. belt today which is getting some age on it anyway, just to see...