battery goes dead, and reads 18v when running.. help!

Srothfuss, I am not sure if you were explaining diodes to me. I know what they are, but that was a nice explanation.

Rather than figuring it out indirectly, one can remove the charge cable and see if the draw reading diminishes. If so, that is the problem.

We dont have Advanced here, but AZ here tests for free (not sure if they have them there).

Good luck.

srothfuss said:

A Diode is a simple electonic device that prevents the flow of current from a source to ground. It's sort of like a one way door that prevents your battery voltage from being drained

Click to expand...

Diodes in the alternator actually convert the AC current (as in alternating, hence the word alternator) that your alternator makes to the DC current that your car uses. A diode is a simple electronic device (as you stated) that only allows current to flow in one direction. If you look at a diode you will see that it has a colored band on one end. That is the end that current flows out of.

If his car is charging at 18v then the regulator in the alternator has gone bad. The regulators in Ford alternators are cheap and easy to replace. No car should ever charge at more than 14.7v.

HISSIN50 said:

Srothfuss, I am not sure if you were explaining diodes to me. I know what they are, but that was a nice explanation.

Click to expand...

Oh no... I was just throwing out a simple explaination for clairification / future search purposes. I knew that you knew what they were... When I was young I figured out the hard way what they do.

Maryland Stang said:

If his car is charging at 18v then the regulator in the alternator has gone bad. The regulators in Ford alternators are cheap and easy to replace. No car should ever charge at more than 14.7v.

Click to expand...

Correct: His alternator is probably shot... I was just trying to explain the purpose of the part with a funny name (Diode).

srothfuss said:

Correct: His alternator is probably shot...

Click to expand...

Actually, it sounds like the alternator is fine. It's the regulator that needs replacing. You need 1 socket and a paperclip to replace it.

91stang50GT said:

so will the battery be drained as a result of the voltage regulator being bad? I am assuming i should try and replace that before pulling the alternator to be bench tested.

Click to expand...

The overcharging may have "cooked" the battery but before you replace it you should test it. There are 3 good ways to test a battery.

1: Aquire a hydrometer from any auto parts store. They're cheap, usually a couple of bucks. To use your hydrometer just put the tube into each cell in the battery and see what the reading is. No cell in the battery should be below 1.225. If there are any cells below 1.225 slow charge the battery for 24 hours. If any cell is still below 1.225 after charging the battery then that cell has failed and the battery must be replaced.

2: Light load test... Turn the headlights on and test the battery voltage. If it is less than 11.5v then charge the battery for 24 hours and test again. If it still can not maintain 11.5v then the battery must be replaced.

3: High load test... Most places that sell batteries can perform this test for you. It can tell you in seconds whether the battery has failed or not.

DO NOT put a new battery in the car until you resolve your overcharging issues.

Good job!

Maryland Stang said:

Actually, it sounds like the alternator is fine. It's the regulator that needs replacing. You need 1 socket and a paperclip to replace it.

Click to expand...

OK, I'll admit to being ignorant. Just exactly how do you replace the voltage regulator? I was told since it was " internallly regulated " that I had to replace the whole alternator.

DEADWOOD said:

OK, I'll admit to being ignorant. Just exactly how do you replace the voltage regulator? I was told since it was " internallly regulated " that I had to replace the whole alternator.

Click to expand...

Yep.

HISSIN50 said:

Yep.

Click to expand...

Nope, it is easily replaced. It's been a while since I replaced the regulator (3 years) in my alternator so these instructions may be a little rusty. Although there are a few steps to it you basically remove the screws that hold the regulator in and carefully, oh so carefully remove the regulator from the alternator. There are springs in the brushes and if you just yank the regulator out the springs may fly off into another dimension never to be seen again. Then you put the springs into the new regulator, push the brushes back and retain them with a paperclip and install the new regulator. Pull the paperclip and you're done.

The first time you do it may take 10 minutes but you will have actually done a real mechanic's job. You fixed something instead of just replacing it.

Interesting. I knew the reg was removable but did not think you could find new ones (not that I honestly looked too hard). My bad. Good info.