Overcharging batteries causing batteries to boil?

Hello, I'm Danny.

Just a few questions first. This replacement alternator was it a remanufactured unit or brand new? Was it replaced prior or was this a first replacement? It's voltage regulator is way to high putting out 18 volts. Normal output should never be over 14.5v . This guide should help

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let us know and we'll go from there. Hope this helps and thanks for using 2CarPros.

Hello again.

Okay. How long ago was this replacement? Is it still under warranty and what brand alternator from AutoZone--- A Duralast?

Danny-

Hello again.

When you say you noticed the 18v output is that on the trucks instrument panel gauge or have you used a dvom - digital volt ohm meter on the alternator output pole?

Danny-

Hello again.

Okay, that alternator is defective. The internal voltage regulator is ruining your electrical system by overcharging. It should never be over 14.5v I would suggest you return that alternator since it's only 2 months old a requests a new replacement. Hope this helps and thanks again for using 2CarPros.

Danny-

Hi,

I noticed you haven't been contacted in a couple of days. I hope you guys don't mind if I jump in.

First, I noticed you indicated using the DMM at that alternator. That is why you are seeing 18V. This vehicle's voltage is regulated by the ECM, which is after where you checked. You need to check it at the battery.

The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the ECM for diesel engines. The EVR is not serviced separately. If replacement is necessary, the ECM must be replaced. See pic 1 below for location. It's near the fuel filter.

The remaining pics include the directions and pics for replacement. I'm adding them in the event the ECM is bad. However, you really need to check at the battery for voltage. Checking at the alternator is bypassing the ECM.

I hope this helps. Let us know if you have additional questions. Also, we would appreciate it if you could let us know what you find. We're interested in knowing.

Take care,

Joe

See pics below.

Hi,

That is good news. I was reading through this and just wanted to jump in. Regardless, if you are at 14.5v, that's perfect. If in the future you find that changes and both batteries are overcharging, chances are it is the ECM. Let us know and we'll help you through replacing it.

Take care of yourself and let us know if you have questions in the future.

Joe

Hello again.

Glad to hear you were able to fix the problem. Let us know if this problem happens again. Thanks again for using 2CarPros and we will hope you will use our site again in the future when needed.

Danny-

Start by measuring the voltage on the two small terminal nuts on the back of the alternator, then holler back. One will have full battery voltage, the other one must have less but not 0 volts. If it is 0 volts, that wire is grounded somewhere on its way to the Engine Computer. If you find around 4 volts, the computer has control of the alternator field but it is trying to run it wide open. That could be due to a break in the voltage sensing wire going to the computer. That circuit is used for other things too so a break would cause other problems, but a corroded pin in the connector would still let the circuit work but the voltage would be low. The computer would interpret that as needing to increase alternator output.

The engine must be running when you measure those voltages. There will be no voltage there with just the ignition switch turned on and the engine is not running.

Caradiodoc