Strange Problem with Car Battery

Folks,

I’m having an odd issue with one of my cars (a 2006 VW Jetta TDI).

It starts and drives normally, no lights on dash. But if I drive, shut the car off and then immediately try to restart it, it will barely crank. Sometimes will crank enough to start the engine, other times not. But if I let it sit for a while, it cranks and starts fine.

I haven’t timed it to see how long it takes to “recover” but certainly in a few hours it’s back up to full cranking speed/power like nothing happened.

Any idea what could cause this? I mean it’s almost certainly a bad battery but how does a battery magically recharge itself with the car off?

Check for a loose cable connection? Engine heat causing expansion may be doing it.

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Battery cables are tight and all ground straps are too. I’d think expansion would make them tighter, no? This is perplexing.

Did you check the connection at the starter?

If that is OK, the starter may be going bad. Same cause, heat.

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Do a voltage drop check on the cables

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When you are having the problem: Attach a DMM (digital multimeter) to the battery terminals (not any cable). Use big alligator clips for this. If it is around 12.5v or more before cranking, battery is fairly well charged. Watch the voltage when you crank. If battery voltage barely drops and the crank is weak, you’ve got a bad connection somewhere between the battery and starter. If the voltage drops down very low (< 10v) with a weak crank, then the battery has an issue.

Based on your description, I suspect bad connection at the battery. Remove the battery cable clamps at the battery and clean out any deposits (green/white fuzz). Wear safety glasses and use baking soda in water (same recipe for indigestion on the side of the baking soda box) plus an old toothbrush to clean this up. You can also dunk the end of the cable in this solution and scrub it underwater. There will be fizzing. Beware that this process deals with both sulfuric acid and lead compounds, so dispose of the cleaning solution as hazardous waste. Keep this solution away from the battery fill caps. Wash off the cable and battery terminals with distilled water when you are complete.

Apply corrosion inhibitors to the post terminals to help this not happen in the future. Torque terminals to proper specification.

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I’ll do that but last time I had the battery out for some work (about 6 months ago), I cleaned the terminals and put terminal grease on them before reconnecting.

I’ll check everything again and do the test with the multimeter too.

Thanks.

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You’re 100% wrong. It’s the gremlins.

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If the battery test is good, you can repeat the same voltage drop test at the starter. You might need a meter that can record min/max since the meter will likely be under the vehicle. Again use clips on the battery lead stud not the lug. If voltage drops < 10v with weak crank then the cable or connections are bad. If the voltage does not drop then the starter is “likely” bad. There is one other possibility which is excessive friction in the engine but I’d change the starter before going there.

It is not a gremlin … he said it was a 2006 VW Jetta TDI

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So what are the thoughts that the starter is getting hot, expanding against the case of the starter. Then once it cools off, the clearances are looser. If the starter is wearing to where debris is in the case, I could see that.

I’ve had a starter with a bad commutator segment. I also had a rubber mallet that I carried with me at least a year, until one night in the DFW remote South lot where I spent 10 under the truck whanging away it until it would crank.

The starter was replaced the next day. :slight_smile:

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Okay still haven’t had time to check with the meter but this happens every time I drive somewhere and try to restart immediately after stopping.

I just drove a decent distance and arrived home. I’ve been home for 15 minutes. Just went out to try and it cranked up like normal - nice fast, strong cranking after sitting for just 15 minutes at 100 ambient.