I am on my second alternator and still having issues. When driving the voltage hovers around 14V. When stopping at a stop light or coming to an idle the voltage waivers between 11V and 13V.

There also appears to be a temperature aspect to the issue as the variation is less pronounced if not non-existent in the morning during cooler temps, but invariably returns more pronounced in the mid afternoon heat. For example, I had the alternator tested at the local O'Reilly's store in the more and everything checked out okay. Returned at 3 pm and it was showing low voltage output (13 V). That was on the first new alternator. Second one seems to be following the same pattern.

Thoughts????

 

Is it the proper alternator?

 

Have you checked with an alternator tester on the truck? How about a meter? Amperage is more important than voltage. The gauge on the dash could be inaccurate. What problem are you trying to fix?

The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.9 to 15.1 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.8 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

 

Is the pulley on the alternator the correct size? When you get an alternator it usually has the pulley already on it. Changing the size will change the speed at which the alternator is turning and therefore change the charging rate.