i recently picked up a 240 wagon in what i felt was solid condition. a lot of small things but nothing i thought major until i tested the voltage of the antifreeze.

i do not do this often but here and there and after checking this car i will now do this regularly on all cars that come my way. the test is simple. remove the cooling expansion cap and place a multimeter probe in the coolant and the other probe on a chassis ground. the engine block works or even the negative battery terminal. set the meter to DC and use the 2 or 20 volt setting. now read the voltage.

in the case of this wagon the voltage shocked me when i read just under 1 volt..... (.91 to be precise)(normal non destructive reading in my experience are between 0 and . 1 to .2 volts...give or take....much above .6 is cause for worry). this is easily high enough to eat away the heater core, the radiator, the freeze plugs in very short order and really got me worrying if a heater core was in my near future. i was afraid if i flushed the cooling system a now covered over leak would open up. having no real choice i flushed and replaced with fresh coolant and now will pray the core is sound. i could pressure test the core but do not yet have the guts to find out how the story will end.

for those who perform this test i also STRONGLY suggest you perform at the same time this test to determine if you have any voltage leaks into the coolant from the various electrical systems on the car.

to test for voltage leaks into the coolant

1. use probes as described above
2. have some else start the car while your measure the voltage..if no voltage changes take place no leaks
3. if voltage rises you have a leak into the coolant form a poor ground somewhere
4. to narrow it down do this.turn off everything you can, start the car and measure. if it is higher you have a start motor leaking voltage into the coolant. if not turn off the car and turn on every accessory you have and the restart the car
5. measure voltage...... now turn off one accessory at a time until the voltage drops. the last one turned off should be the source system for the leak

here is something you can do to mitigate voltage leaks into the coolant. find yourself a piece of zinc rod or small plate. drill a hole in it and suspend this in the expansion tank. any stray excess voltage will eat away FIRST the zinc rather than the radiator, heater core or freeze caps.

My experience with electrolysis is on marine electricals in salt water (yikes it's scary). It would seem to me that if the engine block has a bad ground to battery neg or chassis a voltage would develop on the block and of course so would the coolant, especially during starting. The coolant and the block would always remain at the same voltage level but I suppose the rad or heater core could end up at different levels. I any event I would always check coolant voltage level in relation to battery neg. When using a zinc it becomes a substitute electrode able to give up electrons easier than other metals, it must be connected to what you are trying to protect. If hanging it in the rad it would do nothing unless it was connected to the rad.

Curious what you did to eliminate the coolant voltage
--
David Hunter

The "coolant voltage" is not caused or impacted by an electrical issue but rather the acidity of the coolant AND the dissimilar metals that are in the cooling system. On average, a 240 cooling system has iron (block), aluminum (head and blackstone radiator), and brass in the heater core. Keeping in mind that the heater core is isolated by a plastic mount, it is probably not a contributor, if this is an auto trans car, the radiator is grounded through the trans cooler lines and could be a contributor.

The key to "fixing" this problem is regular maintenance that includes replacing the coolant along with a good flush! Oh, one more "tip" how about the "different" metal in the cooling system that is introduced by your multimeter probe?

I prefer using a pool water test strip that measures acidity/alkalinity, this measures the actual cause, not the result.

jorrell
--
92 245 291K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

There's a lot of discussion on this "probing the coolant" in the annals of the Brickboard, and just as you see, a lot of misconceptions.

The (original?) article was in a car magazine, I think, and not 240 Volvo specific, but the idea was to find sources of potential differences on metal parts of the cooling system, not to dip probes into the coolant and find out where the nickel plating on your meter probe tip falls in the galvanic series. It went on to suggest re-bonding of things like block to head, radiator, and heater core, and of course, maintaining the pH in the coolant.

Ted is proposing we check with and without the electrical system in operation, as that would be an active contributor not "fixed" by coolant maintenance. The 240 heater core is isolated, the rad is isolated, but the automatic has this very thin, electrically connected brass heat exchanger immersed in the coolant (boy do I dread when that baby fails), and the Ranco heater valve through its mechanical cable. So if poor grounding causes voltages to appear across those items, the measurement would clearly be changed by disconnecting the car's electrical system.
--
Art Benstein near Baltimore

Never test the depth of the water with both feet.