alternator question?

look 171 · 11:21 PM

What's the best way to check my alternator to see if its good or not. When I was following my friends back from dinner earlier tonight, he tells me that my head lights would dim as I come to a stop at a light. I did have to jump start my van after dinner. My battery was completely dead. The head lights could not light up. Any ideas?

Sonic dB · Sonic dB's Garage

get one of those inexpensive voltage readers that go in to the cigarette lighter from the local auto store.... keep an eye on the voltage pre starting and while its running, make sure that you arent getting any voltage spikes or it could be voltage regulator going bad.

lm6y · 06-08-2009, 04:05 AM

When's the last time you cleaned the battery terminals?

masraum · 06-08-2009, 04:22 AM

Check the voltage of the car with the engine running. You're expecting 13.5-14.5. 12 or 12.5 would be bad. Even 13 would probably be ok, but most cars run in the 13.5-14 range.

Paul K · Paul K's Garage

Some auto parts outfits can bench test alternators. Is the voltage regulator in the alternator, or on the sidewall?

legion · 06-08-2009, 05:02 AM

What type of vehicle and how old?

On my 951, something wouldn't work right unless it was at exactly 13.5 volts. (Mostly the gauges would read low.)

On that car, I ended up rewiring the headlight, replacing the main ground, having the alternator rebuilt, cleaning all of the other grounds, and replacing the battery before the electrical issues were completely solved.

I took the car to an Interstate Batteries shop at one point. They had the voltage at 13 even when the car was running, and said everything was fine. It wasn't.

look 171 · 06-08-2009, 07:07 AM

It is a 07 Toyota Sienna van. I am thinking an alternator should last longer then that. I'll check the volatge this morning before I take it in. I think the battery is just no good. The reason I suspect the alternator is that the battery was completely dead. After I jumped it, the clock was back to 12:00.

Jeff

look 171 · 06-08-2009, 02:35 PM

Quote:

Originally Posted by masraum

Check the voltage of the car with the engine running. You're expecting 13.5-14.5. 12 or 12.5 would be bad. Even 13 would probably be ok, but most cars run in the 13.5-14 range.

It is at 13.4. What do you think?

Jeff

rick-l · 06-08-2009, 03:04 PM

Quote:

Originally Posted by look 171

It is at 13.4. What do you think?

Jeff

Is that on the battery terminals?

lm6y · 06-08-2009, 04:11 PM

Rick is right on the money. Check it at the actual POSTS first. Then check it at the wire terminals. IF there is a difference, the terminals are dirty. It will do exactly what you describe. If the connection is bad, the battery will NEVER charge. Or just clean the terminals and see. You have to take them off to change the battery anyway.

look 171 · 06-08-2009, 08:59 PM

it was check at the terminals. I got another battery at Interstate Battery Today. I will keep an eye out and we will see how it goes. We are driving up to Vancouver in 2 days. I am glad it happened now then on the road. Thanks for all your help.

Jeff