I changed my alternator this morning. Went from a Bosch to a Napa Denso. The install went well, but when I started the truck, the scan gauge II did not pick up the water temp for the intake temp for about 5 minutes. I shut the truck off, restarted, and started registering water temp and intake temp after a few seconds. The alternator is putting out 14+ VDC. Rated at 136 Amps. There were no codes thrown, and yesterday was working fine after my radiator flush/water pump repl/and t-stat replacement. Anyone have any ideas of anything I should check should this recur? Thanks.

What you need to test is load test and AC noise test. A really good bench tester will have the ability to test diode function and be sure its not leaking AC noise. Here is my homebrew test.

Really? that is all that is needed to check for AC leakage: switch between DC and AC? Where to attach the test probes.. at the battery or right at the POS term @ alternator?

Positive to Positive and Negative to Negative. Check DC voltage then Check AC voltage. DC Voltage: 13.5 to 14.5 DC Volts (Passing grade)AC Voltage: Less than 0.1 AC Volts (Passing grade)If you get a instant 31 Volts AC your DVM is low quality and is not capable of measure different frequencies other than 60 Hz household. Oscilloscope is the best way to measure alternator output but not everyone has one.

Positive to Positive and Negative to Negative. Check DC voltage then Check AC voltage. DC Voltage: 13.5 to 14.5 DC Volts (Passing grade) AC Voltage: Less than 0.1 AC Volts (Passing grade) If you get a instant 31 Volts AC your DVM is low quality and is not capable of measure different frequencies other than 60 Hz household. Oscilloscope is the best way to measure alternator output but not everyone has one.

Positive of what to positive of what ?

Positive probe (DVM) -> Positive post of either batteryNegative probe (DVM) -> Negative post of either battery

??

I have a Craftsman DVM, got 14.39 vdc, switched to VAC and it swept down to 0.00 Good to go. Thanks Mike