"is 13.75 volts a bad reading for an alternator?"

Tim,

That depends ...

I don't remember the curve, but the recommended charging voltage varies 
inversely with temperature.  13.75 volts looks fine to me for summer with 
13.8 volts being the standard for room temperature.

Many compromises are made in auto design and the advantages of including 
the voltage regulator in the alternator sacrifices the sensing of air 
temperature in favor of compact design with less complex wiring.  Actually 
external regulators get it wrong as well because what counts is battery 
temperature, not air temperature.

So, if the mechanic measured 13.75 volts on a warm alternator, it is just 
right.

Mike

Michael A. Radtke  -  Z74               Voice: 602-862-4897
Bull                                      FAX:         4853
13430 N. Black Canyon Hwy.
Phoenix, AZ  85029                      Email: m.radtke@bull.com