So how would one go about testing their alternator? With the cold weather (-6* last night) my van seems to be turning over very slowly. The batteries are new. I will be replacing the battery cables and starter, but I want to make sure the alternator is working. My old batteries went dead. The alternator didn't charge them at idle, but would charge them if I drove around for a bit. The battery gauge on my dash does move slightly to the charge side when I increase the engine RPMs. This would seem to indicate that the alternator is charging, but I want to make sure. Both batteries read 12 volts when the van isn't running. What should they read when the engine is running? Thanks

 

YOu can take your alternator to an AutoZoo or Oreillys or elsewhere, and they'll test it. But don't hand it to the nearest pimply wallflower or ring-up-girl. They will just f up the test. Make sure to ask for a manager or one of the tech's.

One time I went to Pepboys, and the teenage retards working their couldn't get the alternator tester to work. They finally just said my alternator was bad, without really testing it. I was skeptical, so I said "Go test a new alternator off the shelf." They installed the new alternator in front of me, then ran the tester. Sure enough, the test said the brand new alternator off the shelf was "bad." So, they didn't know s***. I got a manager, and then they did it right and found out my alternator was good as well as the brand new alternator off the shelf.

If you are replacing everything anyway, you might as well replace your voltage regulator. It might be responsible for your lack or reduction of battery charging. But since it apparently is charging at high idle, maybe your VR is working. Regardless, if you are replacing cables, starter, and maybe your alternator, a six dollar VR should be included on that repair.

 

Thanks. I know a number of place will test them if you bring them in. However, since the high here has been in the single digits I was hoping I could do it without pulling the alternator out of the vehicle.

Replacing the regulator would definitely happen if I replace the alternator. My plan to put in a G3 alternator when this one goes bad. Figured I might as well upgrade while I have it out. Plus if I ever get around to adding some house batteries a higher output alternator would be needed.

 

Engine off put a volt meter to the primary battery, (pass side). Fully charged batteries should give you around 12.5volt reading. Start the truck up, idling you'll want to see around 13.5 volts. Some increase with RPMs is normal. At cruising speeds/RPMS you'll be around 14volts.
My alternator is tired, has been for a long time, and only charges at higher RPMS. Never been a problem for me for when my truck is on I'm driving it.

 

Thanks. I have just noticed with the drop in temps and an increase in my short in town trips it starts turning over slower until I spend some time cruising to charge it back up.

 

If you have a battery charger with analogue meter, you have a charging system tester.
To load test the alternator, run the blower at full blast along with the head lights and defroster etc.
Watch the meter. If it stays above 12.5V at idle, you're charging.
My truck charges at 14.7 at high idle. A little hotter then I'd like, but my new batteries are 4 years old now.

If you were so inclined, you could split the alternator yourself, and do a nasty fasty rebuild.

 

i use a battery load tester.
load test the batteries with cables off. if they pas the test, i hook them up and start the engine.
then i hook the load tester up and load the alternator. if the vehicle shuts off the alternator is bad.
if it stays running, look at the output voltage. this will tell you the alternator condition. if it is above 12 volts it is good. if it is down around 11 volts it is on it's last legs.