Thaddeus

Today I was driving home in Sharky when I saw a fellow putting the top down on his 968 in a park parking lot, so I stopped to chat. I left the engine running and we had a pleasant talk for about 10 minutes. It's about 81 degrees here.

When I got back in the car, A/C running, stereo on, no lights, I saw the engine was at normal temperature... but my voltmeter was running at 12 volts flat. Usually it's at ~13.5.

I turned off everything and drove home. With the A/C off, drivng conservatively, the voltmeter crept up to about 12.5.

So:

I think the alternator is going bad. I have a new battery. Either the fan for the A/C is drawing too much, or the alternator itself overheated while the car was sitting there, or a combination of the 2. Unless somebody else has had this happen, or has a better idea, I am going to replace the alternator.

What say all of you?

Thanks

Thaddeus

Red UFO

When that happens to me on Battery #2. its because the positive connector merely came unscrewed, cheap fix.

Did you check the battery connection?

Thaddeus

I will check. I suspect it's tight though, I was mighty careful whe I installed the battery 2 months ago...

the flyin' scotsman

Thaddeus...........if you have a multi-meter check the voltage of the battery with the car at idle and then have a helper rev the engine. A significant rise in voltage (2~2.5 volts) would indicate a healthy charging system............a zero or low rise would indicate the alternator is not providing enough output.

There may be no issue at all as with the car at idle most of the electrical energy is from the battery; its only after the alternator spins above a certain level that it provides most of the necessary power for all electrical components as well as charge for the battery.

Thaddeus

It has traditonallly always run at above 13 on the gauge... this is a change, and not for the better.

the terminals are clean and tight. I put the charger on the battery to get some idea of the state of charge... the battery started drawing at 5 amps and dropped down to 2 in about 4 minutes... which is typical for that particular charger and a healthy battery...

I am going to start the engine later after it's all cold. If it's back to ~13 then I'll know something's up that's temp related.

Randy V

On these cars, I'd usually suspect the gauge before the alternator.

Bill51sdr

Thaddeus, I have always noticed my volt gauge drops in voltage as the electrical system has an increased load, especially at night with the headlights on. As Randy is getting at, this is a common condition in these cars. You had a lot going on with the A/C running and the cooling fans drawing a lot of current whie the engine was idling. To put your mind at ease, put a meter on the battery terminals with the engine running and see if it's being charged or not.

Thaddeus

I drove the car again. Same deal with the voltage gauge-- just a smidgen over 12. And when I stopped the car and shut it off, I could hear the electrolyte bubbling in the battery! I think there must be some pretty serious discharging going on!

I think it's new alternator time...

Thaddeus

Well, when the engine is cold, the reading is at 13.5. So when it isn't super warm, I'm getting adequate charging.

HYPOTHESIS:

When it is very warm under the hood, the belt on the alternator expands/gets more stretchy and begins to slip. Alternator then does not make enough juice to account for electric cooling fan.

Going to tighten that bugger a bit and see what gives.

Sharkbait

What should I be reading on my gauge while driving? I am around 12.5 or so and it drops to 12 when I run AC and radio. I've never seen it where I'd consider it 13 or higher and never ever near 14.

Thaddeus

13.5 is where it's supposed to be when charging. But these factory gauges are crap; test it with a good voltage tester.