Battery Voltage Readings - Different Ground Points - Different Readings

[Al P.]

This seems very odd to me, but when I check my battery voltage with my digital VOM, (Car Parked) Positive lead on the + battery post and Ground lead of the meter to engine block or frame etc I get a reading of 12.76V.

When I move the negative lead of the VOM to the Aluminum Radiator I get a higher reading of 13.3V. Anywhere else other than the radiator for ground shows the same 12.76V.

Is this normal?? Why does the voltage look higher when grounding the VOM negative probe to the aluminum radiator?? (When the car is not used the battery is always disconnected)

Makes no sense - or does it?

[Wayne W.]

Re: Battery Voltage Readings - Different Ground Points - Different Readings

The radiator is pretty much isolated by the rubber mountings. The support should be grounded.

[Michael H.]

Re: Battery Voltage Readings - Different Ground Points - Different Readings

That's interesting. I'll have to try that test. I suppose the radiator is somewhat grounded through the carbon black in the mount and radiator hoses. That certainly doesn't explain the voltage increase though. ??

[Al P.]

Re: Battery Voltage Readings - Different Ground Points - Different Readings

That's interesting. I'll have to try that test. I suppose the radiator is somewhat grounded through the carbon black in the mount and radiator hoses. That certainly doesn't explain the voltage increase though. ??

Very odd isn't it?? I check again with the negative side of the VOM to the Radiator support which should give me the "normal reading" - Test yours and see if you get same results, Id be interested in that - Thanks!