Outer Limits 4x4 Board

Hey Guys,

So the pootrol ate a all aluminium radiator in three years.
diagnosis was stray current.
trying to find the source, I had all sorts of strange things going on with it last week and advice was get a analogue mulitmeter, and flush the system so you have water only in there.

OK, thats done.

So I went to it this morning, bearing in mind I filled and drove and drained the cooling system about 10 times at least last week with tap water to get it as clean as I could, and it is clean water in there now and I havnt driven it since then.
went to it and with everything off including ignition, it was reading 0.5 V
FUCK I thought to myself...
so I started unplugging things from the battery 1 by 1 until there was nothing left.
still 0.5V (depending how far you dip the probe into the coolant)

So I disconnected the USI-160 battery controller, no change, and started disconnecting things from both back batteries until they were isolated completely, IE no earth or power connected to them. Still no change.

Then I thought, ahhhh of course, the laminova intercooler has coolant mix in it, that must be storing a current blah blah, checked that and it had -ve voltage of about 0.2V
FUCK I thought, so I have no drained that and flushed it with water and then blown the lines dry so there is nothing in it, to eliminate variables.

Feeling chuffed that I had got it sorted and there would be no stray current now as all 3 batteries do not have their +ve terminal connected and only the cranking battery has its earth on, I check again.
0.5V STILL!

So I am stumped.

I ran some water into a bucket and tested that, 0.2V with both probes in the water.


No I am a little confused so I have supplied photos...
but basically the digital multimeter set on 2V (cause on 200mV it maxes out) reads 0.5V
the analogue one read higher earlier (5) but as in the photo is reading around 2.4 and as per the chart it says multiply by .01 (2.4*.01 = 0.024) photo doesnt show it, but yes it is in 0.1V setting...

SOOOO, is the digital or the analogue gauge right?

photos for reference:


The test piece:





the reading on the digital meter as shown in the arrangement above




and the analogue reading (pulled probs from digital and plugged to analogue)



reference table







Reading in the bucket (I know the analogue one is a bit hard to read cause its off centre, but its ~0.2) so 0.2 * 0.01 = .002




Why is the digital and analogue so different?!




And more to the point, why does my water have a voltage?!

the tap water and the water in my coolant....

Just for reference, on 20v setting on the digital gauge it reads 12.01V on the battery and 0.5 something in the coolant, so that scale seems to be correct...

blew the ass out of the analogue one by sticking it on the battery in the wrong setting...oops, might be taking that back for a swap over

any and all help appreciated guys!



Cheers, Andy

Asking a very basic question, but have you taken an earthstrap from the radiator direct to the engine, and not simply to the chassis?

Contrary to most opinion, the biggest, fattest earth wire goes direct from the battery to the engine to act as a return for the starter. All chassis and frame earths have their return via rusty metal and thin (generally corroded) cable to the battery. If your radiator has an earth to the chassis it is possible to generate a voltage drop relative the the engine earth due to all the other electronics drawing current (V = IR), in particular these days ECU''s, TCU's, and other electronics when the engine is running.

Try a big fat earth strap from the radiator to the engine block instead of the chassis.

The only "real" earth is the negative terminal of the battery, next best is the engine block, then the chassis.

Electrolytic oxidation if that is the problem may be better solved with a standard radiator (consider looking into electronegativity aspects of chemistry - been decades since I did HSC chemistry)

How is the radiator mounted? Is it insulated from the body? Most modern installations have rubber mountings which act as vibration dampers and also insulators. I have looked up the charts and have found a range of galvanic voltages for aluminium, depending on the composition of its alloying elements. The voltages range from -0.75 to -0.9. Cast iron is about -0.5 volts, so I cannot see your readings being entirely due to the galvanic differences. (Don't ask me what they are due to).

I think it would be better to isolate the radiator from the engine, rather than to earth it directly, because you would only be inviting more current to flow, and aluminium being lower on the scale, it would be the aluminium which was sacrificed and your radiator would fail. The fact that you have 0.5 volts (presumably between the aluminium and the car body - earth) suggests that your radiator may already be insulated, but maybe not well enough. When you are moving, maybe it is making contact with the body.

Another one to check would be the earthing of the body to the battery. Maybe you have a lousy connection near the engine bay. You may well find 0.5 V between the body and the battery earth (again, I don't know why).

As for the water having voltage, I think it is in the meters you are using. Probably different metals in the leads/connecttons etc.

Yeah rad is isolated and I will keep it isolated. I agree that earthing it and increasing flow only makes it worse.

I think I am going to put a sacrificial anode in there, clean all the earths and be done with it.

You also jogged my memory, I actually had to get an indentation from a bolt head welded up as it was nearly through the tank, so I am thinking it is a combination of factors that has brought this about.

Still chasing the issue though so please keep throwing ideas out there


Cheers, Andy