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Help: Battery Drains When Engine is Hot

This is a discussion on Help: Battery Drains When Engine is Hot within the External Engine forums, part of the LSx Technical Help Section category; I am having an issue where my car (2001 WS6 with 190K miles) starts fine and the voltage is around ...

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    Help: Battery Drains When Engine is Hot

    I am having an issue where my car (2001 WS6 with 190K miles) starts fine and the voltage is around 13.5V when I start the car cold. Then once the car warms up, the voltage drops to around 11.5V and if I accelerate hard, it will drop into the red area and then go back up to 11.5V(~8V; this doesn't happen if the motor hasn't completely warmed up). Once it drops to 11.5V or below, if I turn off the car, I will not be able to restart it until the motor cools.

    I have replaced the alternator with a brand new truck alternator (140A) including a new four position, single wire connector, the battery with a new 700CCA battery, and the starter with a rebuilt starter. If have wiggled all of the wires that I can get my hands on to see if the meter will move up from 11.5V, but none of them caused any changes.

    Also, there are no codes.

    I am thinking about replacing the serpentine belt tomorrow, but it is less than a year old.

    Any ideas?

    - Tom

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    Something that fails when hot is almost always an electrical component. The fact of the aletrnator being "new" doesn't seem to mean a whole lot these days. I have had several parts fail upon installation, or shortly thereafter, that were new. If your belt were that loose you should be able to easily tell and would probably have some noise. Check the voltage with the engine at idle and then hold the rpm around 2,000 and check it again. The single wire alternators can be finicky.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Have you checked your ground points? 1 on the fender near the battery, 2 on the block.

    Are they are corroded? Also look at the battery terminal connectors.

    Do you have an aftermarket stereo system, amps?

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    No aftermarket stereo or amps. I will check the ground connections. The battery terminals are clean and the battery is new as of two days ago.

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    Have you verified the charging system by checking with a voltage tester? See if it jives with what you are seeing on the factory gauge in the car?

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    Actually, when the car is cold and off, I measure 12.9V at the battery. When the car is cold and running, I measure 13.5V at the battery and the indicator in the car appears to be around 13.5V or so. When the car is hot and running, I measure 13.5V at the battery and the indicator shows around 8-9V. At this point, if I turn off the car, I measure 12.9V on the battery, but it will not start until the motor cools a bit.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Loser View Post
    Actually, when the car is cold and off, I measure 12.9V at the battery. When the car is cold and running, I measure 13.5V at the battery and the indicator in the car appears to be around 13.5V or so. When the car is hot and running, I measure 13.5V at the battery and the indicator shows around 8-9V. At this point, if I turn off the car, I measure 12.9V on the battery, but it will not start until the motor cools a bit.
    The fact that you show it's charging at the battery with a volt meter when hot, yet your gauge is showing much less (8-9volts) Is a clue.

    Tells me your alternator is working and charging the battery, but you have something funny going on between the cars gauge and the alternator.

    Might be time to break out the GM manual and start going throught the checklist procedures and pinpoint it.

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    Senior Member Orcus79's Avatar
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    To help further, can you describe not starting? Does it turn over like normal and not fire or sluggish to not at all?

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    Quote Originally Posted by Orcus79 View Post
    To help further, can you describe not starting? Does it turn over like normal and not fire or sluggish to not at all?
    It turns over very strong, but it doesn't even try to start.

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    Ok, then the suggestions above would be the best place to start. Chances are proper voltage may be getting where it needs to causing the no start. ECM isn't getting proper voltage or the computer doesn't think it's getting proper voltage. Just vague guesses though.

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    Our cars seem to be very sensitive to fluctuations in the electrical system. When the battery started to go in our car all sorts of weirdness ensued.
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    Quote Originally Posted by pajeff02 View Post
    Our cars seem to be very sensitive to fluctuations in the electrical system. When the battery started to go in our car all sorts of weirdness ensued.
    Yep, electrical problems are the worst and my least favorite. Especially on a car with so many electronically dependant gadgets. (dont' get me started on that )

    Definately something odd going on if the car cranks just fine and won't hit, and the fact it only does it when warm,,,,yet starts up fine when cold.

    That oddity would just about make me want to sell the car and go buy another one. I'd probably go as far as pulling that alternator and testing the diodes (can do it yourself or take it to a competent shop) Not sure if the autoparts stores will test for that or not on their machine. But I've had them charge fine but a bad diode would draw the battery down while sitting. Since there is an odd relationship between your volt gauge in the car and what the car is actually charging when checked with a meter, I can't help but think there is something wrong with that alternator. It's a long shot.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Hey just a while pitch in the dark, but have you checked your engine coolant sensor? When mine was busted it wouldn't let me start the car, I think it told the pcm it was too hot. I swapped it out and car started right up.

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    Alright, today I pulled the starter and made sure all wires were well shielded and not contacting the exhaust/cat. I checked all the ground points I could find (one on passenger side of motor, one on driver side with strap going towards the front frame, and one on the drivers side on top up towards the radiator).
    I have a new battery, new alternator, and new starter. I measure 13.9V at all three when the car is running, but the gauge in the car says about 9-10V when hot. I also measure 13.7V at the positive wire going into the fuse/relay block.
    I will pull the alternator next and take it apart to look at the diodes when I get some more time.
    Does anyone know where the gauge measures its voltage from?

    - Tom

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    If you are getting good voltage readings under the hood, no need to yank the alternator. The problem has to be either in the gauge itself, or the wiring to the gauge. Any electrical issues elsewhere in the car?

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    Quote Originally Posted by pajeff02 View Post
    If you are getting good voltage readings under the hood, no need to yank the alternator. The problem has to be either in the gauge itself, or the wiring to the gauge. Any electrical issues elsewhere in the car?
    Not that I'm aware of with the exception that once the gauge indicates low voltage, the car will turn over with no issues but will not start. Once it cools off for about 30 minutes, it starts right up. If I can find where the gauge detects the voltage, I can start tracing from there using my voltmeter until I find the voltage drop.

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    You still have something odd going on then. Test the voltage at the battery terminals and compare it to the gauge reading next time this happens. If the battery were actually low, it should not turn the engine over in a normal fashion. It would either crank slow or not at all. I am wondering if you have a corroded or loose ground wire?

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    Quote Originally Posted by pajeff02 View Post
    You still have something odd going on then. Test the voltage at the battery terminals and compare it to the gauge reading next time this happens. If the battery were actually low, it should not turn the engine over in a normal fashion. It would either crank slow or not at all. I am wondering if you have a corroded or loose ground wire?
    The voltage at the battery is 13.9V and the gauge reads 9-10V. This happens every time the car warms up. When I start it, the gauge reads about 13.4V, then drops as the car warms up. I've checked the ground wires.

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    So I just used my meter to probe around on the car to make sure I could see continuity between all of the places that I thought should be ground and found that the valve cover on the passenger side is not grounded but the one on the driver side is grounded. Is this an issue? The heads on both sides are grounded.

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    Rocker cover has an o-ring style seal and rubber grommets on the bolts. The coil packs are grounded through the wiring harness, so probably not an issue.

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