Car wouldn't start, jumped it, noticed lots of fresh blue corrosion, drove it home, wouldn't restart (battery dead again). Replaced battery. I then popped the hood after driving it to check oil later that day and theres lots of blue corrosion on the *new* battery. The new battery hasn't died yet, but I'm suspecting an alternator problem, ideas?

For the record, I pulled the alternator and checked out the brushes, they're fine (damn!). Alternator regulator?

 

Good that your brushes are good.
Did you clean connections well? Grey metal is not good connection. Need shiny silver of lead post and/or shiny copper of connectors contacting each other.

Which truck? My sig has charging system (22R-E schematic) explained with test points to narrow down where to look.

Best of luck.

 

Its actually on a Corolla, but in my experience, the 86-95 truck crowd actually wrenches and knows their chit. This is real time and no traffic in the general vehicle tech.

The Denso alt. on my Corolla takes apart just like the alt on my 22RE, maybe not the same one, but it does the same job works the same. Problems should also present the same.

Before I reinstall the suspect alt, I want to make sure I don't need a reman alt because to get the alt in or out on this car, I need to loosen engine mounts and jack up the engine to access bolts with a breaker bar... PITA. I have a hunch that the alt is overcharging. Why else would it cause significant corrosion built up on the old, and new battery in a matter of minutes running time.

Here are my brushes, they're fine.

 

We believe you.

Again...

 

A simple test with your multimeter will tell the story about the health of the alternator .

Maybe you did this and just forgot to post.

I would have done this before pulling the alternator.

You cleaned things squeaky clean when you installed the new battery??

 

Isn't the regulator on the alternator? Perhaps you have the wrong alternator for the vehicle.

 

Yes, the reg is part of the alternator. When you pull the back cover off, its the thing that has the heat sink on it. Its the right alt, its been on there 200,000km.

 

Alternator bench tests fine. I'm a little stumped as to why theres corrosion (looks like Breaking Bad blue meth) all over my engine bay before and after the alternator was replaced.

The alternator shop guy suggested the cables may have absorbed battery acid and thus may continue to generate corrosion despite there being no issue with the alt or battery. Is this plausible?

 

Perhaps but one would need to have been pushing acid out of the battery for a long time to have acid absorbed into the cables.

Easy fix replace your battery cables.

You were not using acid to clean the engine and failed to get it all washed off??

 

Take that multimeter and check the resistance in your charge wire, ground wire, heck check all related wires. Or when running, do voltage drop tests on those same wires and that'll tell you if they're good or not.

Also if it's just the blue meth that's forming the problem, cover the battery post, and the connection and really all the visible metal with a good liberal coating of grease. Hope this helps!