voltmeter reading in verrrrry vcold weather

[00 Ragtop Z]

We have been having EXTREME cold here in Nebraska the past week. lows in the -5 to -10 range and highs less than +5. My voltmeter has been reading approx. 15 to 16 volts on start up, and after driving for 15 mintues is still reading nearly 15 volts. Battery is new (I replaced the original equipment battery-4 years old-in the past few days because it gave up in the ultra cold). The gauge reading will gradually settle at about 14.5 volts after longer drive time. (Stock gauges)

Do these voltmeter readings seem reasonable? Mine normally runs in teh 13-14 volt range but I have never had to deal with this extreme cold for this length of time before and wondered if it's just the cold or if the alternator is having a hissy. (It does make some noise for the first few mintues the car runs after start up.)

Thanks.

[detroitgene]

You describe two things that have changed since seeing normal voltage readings: Getting a new battery AND extreme cold temperatures (suddenly?). It's logical that one or both of these is the reason you're seeing voltage readings other than 'normal'.

Let me preface the following by saying your best bet is to have a VAT Test (Voltage Amperage Tester) performed. This can tell you exact conditions of the battery, alternator and regulator. I can only offer some ideas based on the limited info in your post. Sorry if this is long, just trying to help.

A couple of possibilities:
1) Your new battery may not have been fully charged to start with. 'New' battery does not always = fully charged battery. They can sit in stock for a while (slowly loosing their charge) until a cold-spell hits - then they're flying off the shelves. If this is the case, the charging system (voltage regulator) senses the need to help charge the battery resulting in higher voltage readings upon initial start-up. Also, you're probably running the blower motor on High and may have the rear-window de-frost going as well (which sucks a ton of current). Doing so takes away from the charging system's ability to put anything of any benefit back into the battery. Remember, a charging system is designed to maintain a fully charged battery, not re-charge a discharged one. The charging system will only give back to the battery any excess produced by the alternator AFTER the vehicles' ingnition system and accessory load have been satisfied.

After you've driven for a while and things warm up, you probably drop the blower motor speed and maybe shut off the rear de-froster. The system will begin to stabilize, there's more current available for the battery (which it gladly accepts), and your voltage readings return to near normal. Because the new battery has the capacity to hold the charge it's given, you're able to cold-start the car after sitting overnight - even though it may not be fully charged. Your old battery obviously lost its capacity to accept and hold any charge.

2) It wouldn't be the first time it's happened, but it's possible that the extreme cold weather is effecting the voltage regulator within the alternator - allowing it to stay 'open' longer than it should resulting in higher voltage readings. Again, as things warm up, the regulator 'acts' normal and voltage readings return to near 14.5. From my experience in the past, voltage regulators which stuck 'open' usually resulted in readings in excess of 16 - 18 volts.

Hope this helps.