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Yet another coolant question.

On a site that makes aluminum radiators for high performance cars I stumbled across a detailed document on how defective grounding in electrical system can cause electrolysis in the cooling system, disabling the anti corrosion additives and destroying their radiators (the crux of it was "test your cooling system for a voltage in the coolant before installing one of out radiators because if electrolysis ruins it we won't cover it under warranty."

Specifically, it said "A voltage of zero to .3 is normal in a coolant of cast iron engine. Such an engine will be destroyed with time by .5 volts, and engine manufactures are reporting .15 volts will destroy an aluminum engine. "
It said dip one probe of the voltmeter in the coolant(of course not touching the metal) and the other to ground.

So I went out to the hanger with a good voltmeter and with master electrical switch (and nothing else on) measured somewhere between 0.9 and 0.12 volts between the coolant and the heads. Depended a bit on exactly where I touched the heads.

I was and am curious if this is normal (as they did say it's normal to see as much as 0.3 volts in cast iron engines and IMPLIYED that up to 0.15 volts could maybe be normal in aluminum engines) or I have a potential problem .

I have never checked this before in the 2+ years 400 hours we've had this Rotax and doubt anyone ever did in the 9 years this 912 has been on our plane. This AFAIK isn't a check that's part of any annual or common inspection.
So I am inclined to believe this slight voltage difference has always been there.

So I called Prestone coolant tech support and talked to a tech who seemed pretty knowledgable about this issue.
His first response was that any voltage over 0.10 could be a problem, and that the thing to do would be to sequentially shut down all electrical components (radio, strobes, aux fuel pump, etc) and when one makes the voltage drop check for a poor ground in that sub system. But when I told him this was a voltage with no electrical sub systems on he asked if there was any Other reason to suspect electrical corrosion ...such as radiator seepage or signs of corrosion at visible grounding points.
When I told him "no" and none in 9 years he changed his take to saying it sounds like a "if it ain't broke don't fix it" issue.

So my questions are..
# has anyone here ever run this voltmeter check on your coolant in a 912 ?
# would anyone be willing to go out to the hanger..or maybe next time you pull the cowl off... or shop do so and report back what you find? (Once the cowl is off it takes only a few seconds to run this check, or if your Rotax is open rear mount even easier.
# anyone have any opinion, or better yet knowledge :) , of if this up-to-0.12 volts is something of concern...and if so how to address it?

All replies appreciated.
  • Re: Coolant electrolysis, voltage coolant-to-ground?

    by » 11 years ago


    Al,

    I've never even thought of electrolysis being the culprit in car radiators over the years. Makes sense though. My plane is right out the back door so I will check in the morning and let you know. My radiator is mounted with rubber isolation mounts and rubber hoses, so the radiator itself is totally isolated from ground. Will check from fluid to ground at the cyl. head as you did and also from fluid to frame ground. Will also check resistance at same points with master switch off.

    Interesting hypothesis.

    Bill.

    Thank you said by: Al C

  • Re: Coolant electrolysis, voltage coolant-to-ground?

    by » 11 years ago


    Curiosity got the better of me, couldn't wait till morning.

    My readings are .2V (+/- .05) with switch off and .3V (+/-.05) with switch on, reading as you did from radiator fluid to cyl. head. Resistance readings show radiator itself totally isolated from ground. Never had to replace but one radiator and that was due to mechanical failure caused by a screwdriver with a sharp point on one end and a dummy on the other end.

    I have a friend in the radiator business. I'll see what he has to say.

    Bill.

  • Re: Coolant electrolysis, voltage coolant-to-ground?

    by » 11 years ago


    Hi Bill,

    Be interesting if more Rotax owners try this quick test and report in


    Talked to my plane's co-owner today on this.
    Turns out that as part of his business they dissect engines and other stuff checking for corrosion. Says they've never found significant corrosion of blocks or heads unless like in a boats where sea water or lake water was going thru cooling system, or one time where they mistakenly assembled an aluminum head to a cast iron block used a copper gasket. With hindsight clearly not the wisest move. ;-)

    So he, FWIW, ain't too worried about this issue.

    If anyone IS worried one way to squelch the whole issue by going to the waterless coolant... But a that may be overkill for a problem that doesn't, exist.

    I'll be interested to hear what your radiator guy says.

  • Re: Coolant electrolysis, voltage coolant-to-ground?

    by » 11 years ago


    I found this item on a reputable sounding motorcycle site;
    http://www.getahelmet.com/jeeps/maint/dexcool/

    It, interestingly, seems to imply it is perfectly normal to find up to at least a 0.5 volt potential between coolant and ground.

    "...As for deciding when to change your antifreeze, don't go by miles or you WILL certainly have seal and mechanical failures. One interesting spec I found is to use a multimeter. You put your negative probe to the negative post on your battery. You then place the positive probe in the neck of your radiator, making sure that the positive probe touches nothing but the antifreeze. Make sure the coolant is warm but not HOT (this is for SAFETY reasons as well as accuracy of your readings. Always be careful when opening the radiator cap on a warm engine). Your readings (regardless of negative symbol on readout) should be:

    0.2 V to 0.5 V - antifreeze is still good
    0.5 V to 0.7 V - antifreeze is borderline
    0.7 V or greater - antifreeze is unacceptable...."

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