Hey everyone,
I have a 85 f250 6.9 and the last day or two I noticed my head and dash lights going dim. Started the truck this morning to head to work and the start sounded a little weak but once going was fine. After work she wouldn't start at all. Got a jump start and was cruisin again however a buddy of mine (who is a mechanic) took a look at er. Now I know he's not too familiar with diesels and this truck is my baby so I was second guessing him the whole time, but also stayed open minded to his ideas, so now I'm here. He said it was because of the alternator. The batteries in there I bought from costco about 2 years ago, he said that the alternator isn't keeping them charged, which is why the lights are dimming and not starting. Does this sound right? I'm thinking I need new batteries, and a new voltage regulator? Are the alternators known to go out on these trucks(only 134,000 og miles)??? Thanks so much for all your help.

 

Check the wiring. That first, then the regulator. Make sure you have good grounds from the battery neg to the ground/case of the regulator.
You may also want to just yank the alternator and have it tested; most auto parts stores will test it for you for free.
You probably won't need new batteries; having your alternator work will solve that most likely.

 

if Costco batteries are the same ones Wal-Mart sells they could be your problem, I've seen them do weird things. I had one just the other day in a car that fully charged with my automatic charger would not turn it over, half a charge it turn over but not have enough to run the computer so it wouldn't run. My charger works on every other battery.
What I would do is get you mechanic friend to put a load tester on you battery it is a silver looking box that hooks to your battery it can also test the charging system. most parts store also will test your batteries for free

 

The charging system on a diesel won't be any different than a gasser, so I wouldn't discount your buddy's knowledge due to his lack of experience with oil burners.

Take the truck to the closest auto parts store and have them check out the charging system, including the batteries. It's free and takes less than 5 minutes.

Costco batteries are generally well-regarded. I use them in my vehicles and have great luck with them.

Mike

 

Have the alternator tested at AutoZoo or elsewhere. Hopefully they have someone who knows how to do something, so they will actually be able to test it correctly. One time I had a bunch of teenagers test my alternator. They couldn't get it set up right, so they told me my alternator was bad. I asked for a new alternator. They got it for me, then i said, "test it." They tested a brand new alternator off THEIR shelf, and it came up as a fail.

More like AutoZoo's staffing is a fail.

well, most likely your alternator and batteries are fine. I'm betting it's your VR. If you buy from Partsgeek.com or rockauto.com you can get a VR for like $6. Super cheap and easy to replace.

 

how many volts are your batteries getting from the alternator at idle???

that answer might tell you something about VR as well as the alternator.