Voltage drop when car is hot.
Thread Starter
Joined: Oct 2002
Posts: 523
Likes: 58
From: Winnipeg, Manitoba, Canada
Voltage drop when car is hot. When I first start the car or it's cold out the volts are at 14.2. As the temps rise under the hood the volts drop to as low at 12.6 volts. They don't rise back up even when I rev to 2000 rpm. Tried 3 alternators. It's not an alternator issue. If I drive at 60 mph, the voltage creeps back up to 13.4 volts after enough air passes through the engine bay to cool it down I'm guessing.
Did the big 3 upgrade. Ground wire, wire to alternator, wire to fuse box. Very minor change of 0.4 volts higher when car is cold to 0 volt difference when car is hot.
Local Midas shop said "Well it hasn't left you stranded..." In other words they couldn't figure it out.
What am I missing?
BTW, 2001 Trans Am.
Did the big 3 upgrade. Ground wire, wire to alternator, wire to fuse box. Very minor change of 0.4 volts higher when car is cold to 0 volt difference when car is hot.
Local Midas shop said "Well it hasn't left you stranded..." In other words they couldn't figure it out.
What am I missing?
BTW, 2001 Trans Am.
This is extremely typical.
You will want to check voltage at the battery to verify voltage readings, secondary readings from the cigarette lighter or interior sources may not show actual voltage
When hot take the car to an auto parts store and have the alternator tested with the car running to verify that the regulator reacts to the test to minimum specs.
You will want to check voltage at the battery to verify voltage readings, secondary readings from the cigarette lighter or interior sources may not show actual voltage
When hot take the car to an auto parts store and have the alternator tested with the car running to verify that the regulator reacts to the test to minimum specs.
Last edited by chrysler kid; Aug 21, 2017 at 07:27 PM.
Thread Starter
Joined: Oct 2002
Posts: 523
Likes: 58
From: Winnipeg, Manitoba, Canada
I was taking the reading off my scangauge II and a secondary autometer gauge. They all differ by about 0.2-0.4 volts from the dash gauge.
Car starts up like a champ and seems unaffected by the stereo when I turn it on (aftermarket 2000 watt system installed 6 months after I started having problems)
Car starts up like a champ and seems unaffected by the stereo when I turn it on (aftermarket 2000 watt system installed 6 months after I started having problems)
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Thread Starter
Joined: Oct 2002
Posts: 523
Likes: 58
From: Winnipeg, Manitoba, Canada
Ok so last night I replaced the wire that goes to the 4 pin connector on the back of the alternator because it looked chewed up. It was a 20 gauge wire. Replaced the connector with a new one and a 18 gauge wire. Put a wire loom on it as well.
Today voltage is consistently 0.3 volts higher when hot and the lowest it went was 13.1 volts for a few seconds.
On start-up it was at 14.1 volts.
Average voltage was 13.4 volts.
I feel it should still be higher.
Today voltage is consistently 0.3 volts higher when hot and the lowest it went was 13.1 volts for a few seconds.
On start-up it was at 14.1 volts.
Average voltage was 13.4 volts.
I feel it should still be higher.
Last edited by Gripenfelter; Aug 16, 2017 at 10:14 AM.
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Joined: Jun 2016
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From: Central Cal.
If you haven't already done so, check EVERY connection whether or not it looks good on the outside. Corrosion can attack a connection inside the connectors. Then look up the allowable tolerance on voltage. You might well be within that spec. What might not look good to you might be just fine. 13.1 is not a bad voltage level.
Technically the voltage will drop from the alternator as the battery is charged. If the car was constantly throwing high voltage it would burn the alternator out quickly,
My voltage readings at the dash can show almost half a volt lower than a direct reading at the battery.
I can't blame you,it's annoying to read 12.7 on my radar detector, but I'll pop the hood and test voltage at the battery and find 13.2
My voltage readings at the dash can show almost half a volt lower than a direct reading at the battery.
I can't blame you,it's annoying to read 12.7 on my radar detector, but I'll pop the hood and test voltage at the battery and find 13.2
Thread Starter
Joined: Oct 2002
Posts: 523
Likes: 58
From: Winnipeg, Manitoba, Canada
Grounds are fine.
So did an experiment. When the voltage was showing 12.7 volts I turned on the stereo and cranked it. It showed 13.3 volts.
I think Chrysler Kid is right. Voltage is shown at alternator output. Voltage at battery during this time was always in the mid 13s.
So did an experiment. When the voltage was showing 12.7 volts I turned on the stereo and cranked it. It showed 13.3 volts.
I think Chrysler Kid is right. Voltage is shown at alternator output. Voltage at battery during this time was always in the mid 13s.
Charging Voltage Hi ALL, the CK Tech is CORRECT.
The best voltage to charge a battery (12 automotive) is 13.4-13.6 Volts.
Years AGO the Voltage Regulator was a mechanical divice with NO "smarts"
TODAY, many inputs control the Alt Voltage Output such as timers, current sense, and temperatures.
The Gauge Reads are often inaccurate, with some in "bits" CAN-2.0B.
I would find ERROR when your charging system did NOT operate as stated.
Lance
The best voltage to charge a battery (12 automotive) is 13.4-13.6 Volts.
Years AGO the Voltage Regulator was a mechanical divice with NO "smarts"
TODAY, many inputs control the Alt Voltage Output such as timers, current sense, and temperatures.
The Gauge Reads are often inaccurate, with some in "bits" CAN-2.0B.
I would find ERROR when your charging system did NOT operate as stated.
Lance
Grounds are fine.
So did an experiment. When the voltage was showing 12.7 volts I turned on the stereo and cranked it. It showed 13.3 volts.
I think Chrysler Kid is right. Voltage is shown at alternator output. Voltage at battery during this time was always in the mid 13s.
So did an experiment. When the voltage was showing 12.7 volts I turned on the stereo and cranked it. It showed 13.3 volts.
I think Chrysler Kid is right. Voltage is shown at alternator output. Voltage at battery during this time was always in the mid 13s.
On my radar detector it would plop down to 11.8 volts when I roll up my slow windows lol. Hard to say if the body control module is just getting worn, or if these cars have always been like this
Voltage readings at the battery are the best way to find true alt strength
Thread Starter
Joined: Oct 2002
Posts: 523
Likes: 58
From: Winnipeg, Manitoba, Canada
Yeah, dash and interior readings always show on the low side. I don't remember it ever being like this before, my original always seemed to just indicate 14 on the dash.
On my radar detector it would plop down to 11.8 volts when I roll up my slow windows lol. Hard to say if the body control module is just getting worn, or if these cars have always been like this
Voltage readings at the battery are the best way to find true alt strength
On my radar detector it would plop down to 11.8 volts when I roll up my slow windows lol. Hard to say if the body control module is just getting worn, or if these cars have always been like this
Voltage readings at the battery are the best way to find true alt strength
So you're right. Something is worn out or messed up that it's giving us wrong readings inside the car.