You shouldn't get any voltage from the radiator to ground. If you have voltage from the radiator to ground then you have something energizing the radiator that shouldn't be. Can't say I've ever heard of that happening though since it should blow a fuse.
If the radiator is grounded then you will get your normal voltage from positive to the radiator.
i read .5 volts from radiator to ground, 12.5 from ground to positive, and 12 from radiator to positive. should i ground the radiator, or will this make the issue worse? is this even an issue, or is this normal?
i probed the coolant to ground and also got .5 volts, the drop is coming from the coolant through the block.
EDIT:
THE VOLTAGES ARE -0.47 FROM RADIATOR TO GROUND, (NEGATIVE LEAD ON GROUND)
AND RANGE FROM 0.00 TO -0.20 FROM WATER TO GROUND, AND 12.37 ACROSS THE BATTERY.
To check for Electrolysis put neg lead to ground and suspend the positive lead in the coolant making sure it is not touching any metal. Your reading should be 0.4V or less. If it is higher flush system until you can get it down. On cars with electrolysis issues I have had better luck with 50/50 mix of coolant using distilled water and an additive or neutralizer like the royal purple stuff. I wouldn't recommend grounding the radiator or heater core, this may cause your problem to intensify. See if you have a bad ground somewhere from a component in your car the coolant is able to say absorb the current and over time the coolant gets an electric charge kinda like battery acid only on a much smaller scale. Grounding that component would actually make that path easier for the current to follow.
What you can actually do to see if you have a ground issue is to watch your meter and have someone turn components on and off to see if anything causes a rise in the voltage in coolant.
Reading the Popular Mechanics link I'd go with checking the obvious signs of ground degradation. Make sure the ground wire of the battery is secure and free of corrosion. Some research should give you info on where grounding straps are located. I'll pull out my Haynes and see if I can track them down.
New results, the results posted above were from approximate memory and are incorrect. The following is what I found today.
THE VOLTAGES ARE -0.47 FROM RADIATOR TO GROUND, (NEGATIVE LEAD ON GROUND)
AND RANGE FROM 0.00 TO -0.20 FROM WATER TO GROUND, AND 12.37 ACROSS THE BATTERY.
I removed the old fluidyne radiator a week ago and replaced it with a oem style unit. I obviousely replaced 2 gallons of fluid when I did this, so the above voltage readings may not rule out electrolysis. Should I try some royal purple neutralizer to prevent this from happening again? or could I still have a ground issue pressent? Thanks!
Ok, I read those articles, (should have read them before I did the testing). Anyway, I let the reading stabilize for two minutes, with both the engine off and on. I got -0.060 volts consistently. Is that good or bad? some say no more than .400 or .200 or .015? which is it? Also, is that supposed to be negative or positive? The articles are not specific. Thanks!
I would think that is ok. Here is ford's recommendations on how to test for electrolysis.
Determine whether coolant condition is acceptable.
Remove both cables from the battery and ensure they do not contact each other or the vehicle.
Touch negative lead of voltmeter to engine ground and positive lead in the coolant.
NOTE: POSITIVE TEST PROBE IS IN THE COOLANT FOR TESTING.
Check the voltage in the cooling system. If less than or equal to 0.4 volts (V) OK, reconnect battery cables and proceed to Step 2.
If greater than 0.4 V, flush cooling system thoroughly.
Recheck voltage less than or equal to 0.4 V.
Reconnect battery cables.
Refill the system with appropriate Motorcraft® engine coolant.
Check for loose or missing grounds at static conditions.
Turn off all accessories. Turn ignition on but do not start engine.
Test with ground probe to battery ground, engine ground, and vehicle ground sequentially.
Voltage less than or equal to 0.4 V on all grounds OK.
Any one greater than 0.4 V, check and clean ground cable connections.
Check accessories without using the on off switch on the vehicle instrument panel, use a jumper wire to ground.
Plug in engine block heater, if equipped, and test.
Recheck voltage less than or equal to 0.4 V.
Unplug engine block heater, if equipped.
Check for loose, missing, or inadequate grounds.
Test with ground probe to battery ground, engine ground, and vehicle ground sequentially.
Crank engine but do not start.
Monitor voltage while cranking. less than or equal to 0.4 V OK
If greater than 0.4 V, ground or repair starter.
Start engine and run at about 2000 rpm.
Turn on all accessories including those customer only uses occasionally such as CB radio, cell phone, etc.
Test with ground probe to battery ground, engine ground, and vehicle ground sequentially.
Voltage less than or equal to 0.4 V OK
If greater than 0.4 V, turn off one item at a time until V drops to less than or equal to 0.4 V. Repair ground to the accessory just identified.
Recheck voltage less than or equal to 0.4 V
Turn the DVOM to AC volts.
Check for ANY AC voltage greater than 0.4.
If any AC voltage is present then try turning off each accessory one at a time including blower motor and any fan motors.
If AC voltage is still present then shut engine off and remove B+ from the alternator and tape it up then retest.
If voltage drop is gradual to less than or equal to 0.4 V, the ground straps may simply be overloaded by added accessories. Test by using heavy gauge jumper to ground. If indicated, install heavier gauge ground strap(s) and recheck.