Battery/alternator issue
Thread Starter
Cruising
Joined: Dec 2023
Posts: 14
Likes: 14
Battery/alternator issue
So I had an issue with the battery in my 85 the other day. I let the car idle for 15-20min and noticed smoke coming out from the hood, I turn the car off and open the hood to find the battery boiling and steam coming out from the vents. The battery was untouchable as it was wayyyyyyy too hot. I’ve been having trouble with a battery drain and have ruled out that it has something to do with the LCD. When I pull the fuse the drain is no more. So bought a new battery and did a volt check on the battery terminals when idle and found to have 15.6v, after a couple revs it dropped to 15.2v. The dash read 14.3v at this time. From my research the battery is supposed to be at 14.7v at idle. Is this too high for the battery?Does this sound like an alternator/voltage regulator problem? Should I replace or rebuild the alternator? All thoughts appreciated!
Melting Slicks
Joined: Oct 2003
Posts: 2,189
Likes: 830
From: Chapel Hill NC
2025 c3 ('68-'73) of the Year Finalist - Unmodified
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Id take the alternator to chain auto parts store for testing.
Le Mans Master
Joined: Jul 2004
Posts: 6,228
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
So I had an issue with the battery in my 85 the other day. I let the car idle for 15-20min and noticed smoke coming out from the hood, I turn the car off and open the hood to find the battery boiling and steam coming out from the vents. The battery was untouchable as it was wayyyyyyy too hot. I’ve been having trouble with a battery drain and have ruled out that it has something to do with the LCD. When I pull the fuse the drain is no more. So bought a new battery and did a volt check on the battery terminals when idle and found to have 15.6v, after a couple revs it dropped to 15.2v. The dash read 14.3v at this time. From my research the battery is supposed to be at 14.7v at idle. Is this too high for the battery?Does this sound like an alternator/voltage regulator problem? Should I replace or rebuild the alternator? All thoughts appreciated!
Melting Slicks
Joined: Nov 2016
Posts: 2,256
Likes: 3,082
From: So Cal
2023 C4 of the Year Finalist - Unmodified
Replace the regulator. It's easy to do, and no special tools required. My 85 has its original alternator, but is about to receive its 4th regulator in 40 years. The original was making RFI, the next two went "high voltage".
There's a power transistor in the cluster that fails, and the cluster doesn't "turn off". The draw on the LCD fuse is about 500ma if the transistor has failed. Draw should be about 50ma, IIRC. << My 85 has done this too.
EDIT/ADD: Yesterday when I wrote this response I was anticipating driving my 85 next weekend to a show and shine I attend a few times a year. Next Sunday is Corvette Marque Day. Typically there are 500 to 1,000 Corvettes at this event. When I last drove the 85 in December, it was experiencing high voltage so it needs another regulator. Today's project is get the 85 out, clean it up a little, and change the voltage regulator.
Last night I looked up a regulator on O'Rileys and came up with a Standard Motor Products VR-111. It was in stock, and they were open until 2300, so I got in the truck and purchased one. Including R&I of the alternator it won't take an hour, and my 40 year old OO 1985 will still retain its born-with number matching alternator. Cheers.
There's a power transistor in the cluster that fails, and the cluster doesn't "turn off". The draw on the LCD fuse is about 500ma if the transistor has failed. Draw should be about 50ma, IIRC. << My 85 has done this too.
EDIT/ADD: Yesterday when I wrote this response I was anticipating driving my 85 next weekend to a show and shine I attend a few times a year. Next Sunday is Corvette Marque Day. Typically there are 500 to 1,000 Corvettes at this event. When I last drove the 85 in December, it was experiencing high voltage so it needs another regulator. Today's project is get the 85 out, clean it up a little, and change the voltage regulator.
Last night I looked up a regulator on O'Rileys and came up with a Standard Motor Products VR-111. It was in stock, and they were open until 2300, so I got in the truck and purchased one. Including R&I of the alternator it won't take an hour, and my 40 year old OO 1985 will still retain its born-with number matching alternator. Cheers.
Last edited by IHBD; Mar 30, 2025 at 12:33 PM.
