High Alternator Voltage Question (1 Viewer)

[JTinNM]

I've got an 1997 80-series Land Cruiser with a Scan Gauge II. I just retuned from a 7 hour road trip and notice that the entire way 7 hours there and 7 hours back that Scan gauge was reading ~14.2 volts. It is my recollection that my alternator would start out around 14.2 volts and after a short time drop down to ~13 volts. Is it normal voltage to to be ~14.2 volts for 7 hours, or is it an indicator that my battery or alternator might be starting to go? If it's the latter, what should I be testing? I am using an Optima redtop starter battery and it's gone dead a time or two from an unclosed door or something but it starts reliably and is currently reading 12.5 volts when the engine is off.

 

[COS80]

I don't know what it means, but I did just read, in the FSM, that it's supposed to be 14.2V cold and 13.8V hot. There may have been a range on the values.

 

[baldilocks]

Sounds like your alternator is functioning as it should. I’ve run optima red tops in my diesel pick up for years. Optima suggests replacing them when the battery voltage drops to 12.4v. I just run them 8 years and call it good since it’s supposedly a 4 year battery. I took the truck to a shop in December of 23 for an ABS light. They told me my batteries were at 12.5 and should replaced. Still running them with zero difference in performance starting the Cummins.

 

[jonheld]

Alternator voltage will vary with the state of charge of the battery and the load on the electrical system.
An Optima redtop is an AGM battery. A fully charged AGM battery should read very close to 13 volts when fully charged and at rest.
That said, the OEM alternator will typically charge an AGM battery to 12.7 V and should be putting out 14.4 V when running with no load. If your alternator is putting out less than that, I would put a meter on the output lug of the alternator and get an actual reading. You could have a failing battery or the alternator could be on it's way out or there is a significant load on the system. Either way, I wouldn't rely on the OBD2 monitor when diagnosing.

I have an Odyssey AGM charger that I use for my Interstate AGM batteries, and it will read 100% charge at 12.8, so I live my life very comfortably at 12.7.
I would not be overly happy with 12.4 after a 7 hour drive.