Hey guys, so today i was just going over the engine before we head out for some camping trips, and just checked the charging system. I am getting 13.0 with truck running at idle, and 12.0 with truck off. Book (haynes manual) says volts at idle should be 14.0 to 15.0. Is this something to be concerned about? Or not? Thanks for the input. And yes, the terminals are clean and tight

 

Your charging system likely is fine. What is important here is that the voltage is higher with the engine running than with the engine off.

You could try revving the engine slightly. You should see an increase in voltage. I would get concerned if it was as high as 15 volts, but a reading of around 14.5 volts at say, 1500 RPM would be entirely normal. Changing the load by turning on lights or heater/AC fans would also change the voltage.

I would be a bit more concerned about the 12.0 volts you measured at the battery with the engine off. Normally, it would be about 1/2 volt higher. I would double check the actual reading with another meter just in case the one you are using is not calibrated correctly. The low reading could indicate a faulty battery, or a parasitic draw that may leave you with a dead battery, likely at the worst possible time, (Murphy's Law).

 

Tenths of a volt are important in a lead-acid auto start battery. Whenever a car battery has been recently charged, when you measure it, there will be a "surface charge". This usually measures right around 13.2 volts. Say just a few minutes after shutdown. But it's not an accurate reading.

If you checked the next morning, voltage will be a little lower, at the actual "resting voltage".

Maintenance free sealed batteries (by far the most common today) are fully charged at 12.80 volts at 77° F, in this instance, if you measured 12.0 volts, especially right after shutdown, would indicate a very nearly dead battery.

It might work, but not for too much longer. The older conventional batteries, the type with fill caps on top to add water, were made with a different recipe and will measure 12.65 volts when fully charged, after "surface charge" is removed.

Testing the alternator/charging system - you want to see 13.8 to 14.2 volts right in there in "normal" weather. A little more in cold temperatures, a little less in hot weather. 15 volts is what you'd see at 0° F; something like that.

Turn the headlights, fan and radio etc, on to load up the alternator and raise engine to a fast idle., say 2000 RPM or so. Then measure right at the battery posts. Voltage will droop some, but it should hang in there 14.x

Make sure belt is tight and not slipping, and cables and terminals at both ends and grounds are clean and shiny and tightened securely. Go for a beer.

 

Thanks for the input guys. So just went out to truck, shes been sitting for about 4 hours now, truck off, im getting 11.7 or so. Then truck running, everything is off, im getting 13.3 or 13.4. Turn everything on, heater, lights, and im getting 13.3 to 13.4. No change. The belt is new, and nice and tight. Checked battery water level, and all good. The charging indicator in the truck is reading where it always has. No change there. Also revved engine up while measuring and no change in volts, still 13.4 Soooo??? Lol

 

11.7 at rest would indicate a bad cell in the battery.

 

Great.... thanks again...