positive battery terminal turns black

[ivansgreat]

I don't really know too much about how the whole electrical system and charging system work, but I have a problem with my battery. The positive terminal and the clamp on it will turn black after the truck has been running for a while. Then when I go to start it, it will not start very easily. It will take a while. I will replace the positive wire to the solenoid and scratch off the black stuff off of the battery terminal and the truck will start up right away, but after running it for maybe half an hour the terminal and the clamp on it will be black and it will start up slowly. Also when I am driving and come to a stop the engine whill act like it wants to die, but if I put it in park at a stop, it will not act like it wants to die. I guess its the blackening terminal that is causing this. What could be causing the positive terminal ( nothing happens to the negative one) to darken up and make the engine start up slow. thanks.

[QC]

Does the post look wet? If the battery cover has a bad seal around the post acid will wick up into the lead and the post will turn black, but it also looks wet. But this will happen even when the battery is just sitting. It almost sounds like yours might be getting hot, being it happens while you are driving. I'd check for excessive draw somewhere, or an overcharging alternator.

[ivansgreat]

No, it doesn't look wet. Thanks for the help.

[flyboy2610]

Put a voltmeter across the terminals while it's running and see what the reading is, the get back to us.

[fordman]

a weak altornator and a lose connection to the battery would cause the truck to die when at a stop sign with the brake pedal being held down. that would create too much of a draw on the alternator to keep up with. it happened to me and that was the problem a bad alternator and a weak battery. everytime i hit the brake it would die and wouldn't restart without a jump .

[ivansgreat]

Thanks Fordman.

[bwc302]

This could also be caused by a bad ground (negative bat cable, engine grounding strap, old wire getting weak and causing a short to ground).

In this case it sounds like something is not making a good ground connection. Has the starter, battery cable, or wiring of some kind been recently replaced (since you started noticing the problem)?

Thanks,

Bobby

[qman]

When it comes to starting, the only thing that matters are the mating surfaces between the battery terminal and the cable clamp. If it is turning black or doing something in between the two then something is up. If it is remaining clean between them and turning black on the rest of it you can see, then there's no problem with the connection.

fordman mentioned a weak alternator. I also had a problem where my voltage regulator was shot and instead of charging at 13-14 volts it would charge higher and higher as you increased the engine revs. This caused the acid in the battery to boil and spew out all over everything. On these old trucks, the voltage regulator is a $5 part. Like flyboy suggested, put a voltmeter across there and see what your alternator is charging at.

[ivansgreat]

I'll have to get a votmeter some time this weekend if I can. But, as you said gman it would be ok if the contact area didn't turn black, but it does. Thanks a lot.

[qman]

Does the battery get hot?

You can also go to Autozone and they'll test it right there for you.

But before you do anything, make sure both ends of both battery cables are clean (wire brush) and tight. Make sure all the contacts in your electrical system, including the alternator, are clean and tight. Sometimes just doing that will fix aproblem.

Just called my mechanic. He said that your battery must be leaking vapor somewhere and it's the acid vapor that turns the terminals black. He did second my thought that your alternator may be over charging.

[ivansgreat]

Thanks for giving me some great info. I'll have to check if it gets hot. If the alternator is over charging, does it have to be replaced?

[qman]

Not necessarily. If the battery is receiving too high a voltage, it's the voltage regulator that's bad. The alternator can generate higher voltages than 14V but the regulator doesn't allow it.

[ivansgreat]

Could it be the overcharging that is making my engine stall when I come to a stop, or could it be that the connection to the battery is hindered by the black stuff. It only stalls when in drive or reverse.If I come to a stop I usually have to put it in park because it will want to turn off.

[qman]

I have no idea as to how electricity would have anything to do with stalling. It could be stalling because your idle screws need to be backed out to give more air to the engine to burn the idle fuel.

[ivansgreat]

ok i've decided to replace the voltage regulator. But, apparently there are two types. There is one with a "trans reg" and one without it. Does anyone know what the difference is or what a "trans reg" is?