I am having hard starts in the cold. I replaced the batteries with two 850 CCA 's. Last week. It was 15* outside as well. I am thinking maybe the started but I want to check the alternator first.

Thanks
Chris

 

Use a dmm. Check your bats with the enging off and then check with the engine running. THat will tell you what your batteries are getting from the alternator.

YOu can always take it off and have it bench tested, or the old fashioned way- start the truck and take wrench to test the magnetism of the alternator.

 

Started out at 11.80VDC and after 15 mins of driving it went to 12.20VDC. What is this telling me?

 

Sounds like the alternator is taking a nose dive. Volts should be between 13.5-14.5

 

autozone
advanced autoparts

 

I tested mine by running the motor and disconnecting the batteries.. If the engine dies, it's probably the alternator.. Sounds crude but it worked in a hurry .

 

i have used this method in the past and it works great

 

be careful: without a battery load the alternator can spike up to 17 volts and fry computers really fast.

my $.02, btdt

 

You are lucky, that used to be the simple way to check it, but nowdays it is not a good thing to do. PIOTRSKO is right, disonnecting the battery nowdays will not necissarilly always work, at least on gassers. However, on diesels it will be an effective test, but as previously stated things can go wacky and your computer will wind up toast. The right thing to do is test all three. I would take your truck by an autozone and see if they will help you test the items out. If the batteries are good, and properly charged they should measure at least 12.3 to 12.5 volts. More important is their load capacity. Disconnect the cables so you can test the batteries independant of each other, then have them apply their load tester to the batteries. A single bad battery in the pair can cause the combined voltage to drop, while simultaneously dropping the voltage while the truck is running since the alternator is having to work overtime to try and charge the bad battery. If the batteries are good , and the alternators are good, then the running voltage in the system should be around 13 to 14 volts. Since you say it was cold out recently. I would look to the batteries, since the cold puts an extra strain on them and they fail more often in extreme temperatures (hot and cold). If the batteries load test good, then remove the alternator and get them to bench test it. Another thing to look is at the ends of the cables. I have seen instances where the insulation is good and yet when you peel it back the cable had so much internal corrosion that it fell right apart. Check both the ends on the batteries as well as the main lead on the alternator. Hope you get it fixed.

 

Thanks ALOT for the great info! Gota love this place. Nicest forum and the nicest people on the net.

Chris

 

You are right, these things can happen. Although in my case the truck ran fine, started up fine, but the battery light was constantly on. So I guess I pretty much knew it was the alternator and my little test simply verified that. On these trucks I don't see that method as being too much of a risk as long as you don't sit there with the thing running without batteries.

Good points guys..

 

If he unhooks the batteries and since the alternator seems marginal (he has no idiot light) it could stay running? With the voltage at the battery so low I would bet on the alternator.