Electrolysis in cooling systems

[Huw Powell]

> Anyone have any experience with this topic as it relates to cooling
> systems?

No, not really...

> I've replaced a couple of radiators each one leaked at the
> seams after about 6 months.

Might be poor quality radiators, but judging by that site someone posted 
on the problem, sound slike you should look into it.

> Should the radiator be grounded to the frame or isolated from it?

I've been thinking about the Audis I've had, and in all cases it seems 
that the radiator is, at least by accident, isolated electrically from 
the chassis - the mounting points are all rubber insulated stud things, 
and of course the hoses are rubber, too.  Although, I've never measured 
the resistance of these "rubber" components.  I suspect you could get 
leakage to ground (or a positive voltage) via either the fan 
thermoswitch or fan motor being faulty.

> According to the info I've read you can check for electrolysis by
> inserting a voltmeter positive lead into the coolant and tying the
> negative lead to ground. My '86 5kcstq makes around minus .3 volts on
> the meter when I do this. My other car makes minus .4 volts (7 year old
> radiator). I've read that anywhere from .1 to .4 volts is bad. Not sure
> about negative voltages.

Again, according to my copious knowledge on the subject derived from 
that one web site, it sounds like you should investigate where that 
voltage might be "leaking" from, kind of like checking for battery 
drains only more difficult.

I also wonder what the possibilities are of the system itself being a 
bit of an electrolytic cell in and of itself - there sure are a lot of 
different metals involved, with a handy possible electrolyte (coolant) 
in between them.

It could be that it's time to flush your system and refresh your 
coolant, first, since the whole problem seems to depend on coolant 
carrying some of this current.  And I don't think it should if it's 
clean (chemists, please?).  I think coolant is basically a sugar/alcohol 
kind of chemical, which should not conduct electrocity well.  Once it 
has become acidified or contaminated by usage by-products, who knows?

Of course, since you are replacing radiators quite often, I guess your 
coolant must be pretty fresh.

Any more bright, uninformed opinions to add to mine out there?

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/