Alternator Replacement on '05 Lariat
 

I replaced my factory battery with an Optima and after 5 months the truck would not start without a jump. The guy at Advance told me I needed a new alternator based on the voltage readings. Was wondering if anybody has had this problem or ever replaced one? If so do you have any recommendations.

does it only start with a jump? or can you jump it then go to the store and shut it off and a couple minutes later restart it without a problem?

Get it running and put a meter to the hot lead of the battery. If your alternator is working, you should see around 14V. I would always verify myself before buying parts.

I would have him show me the readings while he's checking it and also did he do a diode check? What RPM did he do the check at? I always do it at about 16-1800 RPM. It's pretty easy to check but I don't trust some of those guys at parts stores as far as I could throw 'em. I'm sure some of 'em know what they're doing and I'm also sure some of 'em don't!

14V is good, I like to see it a little higher-14.2-14.4, but I am not real excited to see it under 14.0 much, especially at 16-1800 RPM

Another thing to keep in mind...a bad battery can give you false voltage readings, even when running. The shop I work at used to sell and install Optima batteries. Honestly I hate 'em. About 90% of the ones we installed came back within a month with a dead battery. This was over a 3 year period, so it wasn't just a bad batch of batteries either. We no longer carry them for this reason, we were losing a ton of money on the warranty.

Unless you have a big stereo, do a lot of off-roading (high vibration, etc) or otherwise have a special application, a regular lead-acid battery is all you need. The Optimas are built for special application vehicles and from what I've seen, when used in normal applications they have a high rate of failure.

Here's a simple test for you to tell if the alternator has any issues. First check the output voltage by starting the truck, let it run a few minutes, then put a volt meter on it. It should read about 13.8 at the lowest to 14.8 at the highest although I've seen some high capacity alternators have higher voltage outputs. If that checks out, look at the alternator. You will have a shielded cable/wire that bolts to the back or the top of the alternator. Remove the bolt. Now, when you remove the wire, if you see any minor arching of electricity, the final diode is bad allowing the juice to flow back out of the battery into ground via the alternator. No arching- no problems with the alternator. The battery is the problem or you have an accessory that is drawing amperage.

Labnerd- That is a simple and effective tip. I appreciate it and I'm sure there are many others here that will benefit from it. I'm am such a tool junky that I am used to relying on the equipment, but always appreciate the simple ways to rule-out. I always enjoy your answers and tremendous contribution to the forum. I seldom fail to learn something from them!