i've read somewhere that measuring the voltage drop between the coolant in the radiator and the body ground is an indication of when to change the coolant. is this a realiable way of determining its time to change?
I have only read about people doing it and have no experience with it. Here is a forum link that mentions the technique:
"You can also use an ordinary digital volt meter for the same purpose. With the engine off, touch the voltmeter positive test lead to the radiator or engine (making sure you get good metal-to-metal contact). Then open the radiator cap and insert the negative test lead into the coolant. A reading of up to 0.2 volts is considered acceptable and indicates the presence of reserve alkalinity in the coolant. If the coolant reads 0.3 to 0.6 volts, it is borderline and should be recycled or replaced. A reading of 0.7 volts or more would tell you the coolant is overdue for a change.
Internal corrosion in the cooling system can occur regardless of the condition of the coolant if voltage from various accessories (alternator, starter, ignition, etc.) flows through the coolant to ground rather than follows the intended ground path through the ground strap between the engine and chassis or the ground cable between the engine and battery. You can check for this condition by also using your DVOM. Use the same hookups as before to measure the voltage of the coolant, but this time while cranking the engine, then with the engine running and lights and heater on. If stray current is grounding through the coolant, you'll get a voltage reading. More than 0.15 volts can corrode aluminum, and 0.3 volts can be harmful to cast iron. Check, clean and tighten the ground straps and/or battery ground connection to eliminate the problem."
Hopefully someone with experience will chime in.
Checking for excessive electrolysis is not just simply putting a probe in the coolant and testing to one ground or touching the side of the radiator. There are several checks that must be made to rule out possible causes. During testing, utilizing a DVM, if the reading is 400mV or greater the vehicle could have any of the following problems:
-Chassis Ground - loose, missing, or corroded
-Engine Ground - loose, missing, corroded, or undersized
-Added electrical devices overloading engine ground strap.
If the cause of excessive electrolysis is not determined the inhibitors in the new coolant will deplete faster than normal and also the voltage will seek a ground path. The most likely path would be the heater core, radiator (if metal), or water pump seal; could cause other engine damage.
If you have excessive electrolysis it could be the coolant or it might not. If you do not determine the root cause flushing and refilling the cooling system could only be a Band-Aid.