Faulty alternator diode

Someone told me on another forum that an open diode can
1)pass unregulated voltage to the battery.
2)The voltmeter can be fooled into seeing AC as higher DC voltage.
Are these statements true? The person that I am trying to help has high charging output not real high.. I have always seen a lower DC charging voltage..the ones I have seen were shorted and battery drained koeo. Just like to learn the truth. Any input would be appreciated.

I cannot confirm, nor disprove either of those statements. What I can say is that a failed diode will cause an excessive amount of AC ripple in the charging system. Excessive AC ripple can, and will, play all kinds of havoc on the electrical system. The best way to test for this is with a Labscope. Alternatively, you CAN use a volt meter set to AC. I prefer to see less than 200mv AC - 300mv AC. However, many people use 500 mv AC ( .5 or 1/2 volt AC). If you have a reading of .5 VAC, or higher, replace the alternator.

Thanks Chad. I usually check with scope but someone told me the above statements and didn't know if it was correct. Always open to learning if correct.