Stray Voltage in the Radiator Fluid?

[Tonker1]

Hey,
So I just replaced my copper radiator with an aluminium unit. Since I was installing a new unit I went through all the checks, when I was checking for stray voltage in the radiator fluid, I found there was 0.5V stray (apparently this should be a maximum of 0.05V). This went up and down when I turned on indicators, revved the engine, used the headlights, essentially altering anything that used electricity changed the voltage of the fluid.

Does anyone have any idea on how diagnose and resolve this problem?

Thanks in advance!

[Strawdawg]

I would take my meter and check the voltage drop across my grounds...battery to block, block to firewall/inner fender  and firewall to battery to see if it was less than a couple of tenths of a volt as a starting point

[Strawdawg]

I am assuming that you have relatively new, or new, coolant in the system....

[dodj]

I would take my meter and check the voltage drop across my grounds...battery to block, block to firewall/inner fender  and firewall to battery to see if it was less than a couple of tenths of a volt as a starting point

Your block to firewall ground probably needs cleaning up/tightening. If the block to firewall ground connection goes up in resistance due to corrosion etc, the path of least resistance starts to become the coolant. The engine block, and coolant inside it, ideally, should be 0v to ground.

[Tonker1]

Where should the block grounds be a 340?
Currently when looking at the engine, the battery negative terminal is connected to front of the drivers side cylinder head and the chassis is connected to the front of the passenger side cylinder head (sorry for the photo quality, the camera is having a mid life crisis). Are the cylinder heads acceptable points, to me logic says no? But, then again the spark plugs are ground through the heads so it shouldn't be a problem.

I would measure what the voltage drop is, but my battery is currently 80miles away in my brothers car. I woke up in the morning and found a note in it's place saying "Cheers bro, mine went died spontaneously, needed yours"! The battery will be back in a days time and I'll let you know then.

[Bullitt-]

Ground strap goes from the passenger side valve cover bolt to the firewall near the voltage regulator.  Flat braided wire about 1/2" wide was OE. 

[dodj]

There is a 5/16 or 3/8 threaded hole on the back side of the passenger side head that I've used for the ground stap.

[Tonker1]

So the battery is back in, turned the engine on and took some measurements.
Battery -ve terminal to +ve terminal                   14.01V
Battery -ve terminal to radiator flui          around 0.52V
Battery -ve terminal to engine block                    0.00V
Battery -ve terminal to chassis ground                0.00V

So essentially the current in radiator is 10 times the acceptable maximum and it would ideally be 0.00V

I'm not sure how to start diagnosing the cause of the issue. Any ideas or previous experience with similar situations?

[nqkjw]

It's caused by bad earths and not necessarily the obvious main earths you have already checked.
Abt 10 years ago I purchased a brand new 23ton Komatsu excavator.
Within the first year they replaced three corroded radiators under warranty.
Then they got serious.
They stripped ,cleaned and reassembled EVERY earth on the machine.
24v machine.
Their specs said maximum of 0.04volts (close enough to same specs you have)
Excavator had 0.13v stray current.
After re-earthing everything it had 0.004v stray current.
Problem solved.
No more radiator issues.

Apparently a good earth directly to the radiator helps.
The Komatsu excavator runs one from the factory and it's the first thing Komatsu fitters check when there is a radiator problem.
The std earth to rad is in a stupid place.It's easy to step on it and break it.

[Tonker1]

It's caused by bad earths and not necessarily the obvious main earths you have already checked.

Oh right, I didn't realise it was more than just the engine grounds that were of concern.

Apparently a good earth directly to the radiator helps.
The Komatsu excavator runs one from the factory and it's the first thing Komatsu fitters check when there is a radiator problem.
The std earth to rad is in a stupid place.It's easy to step on it and break it.

Wouldn't grounding the radiator just aid the current flow trough the radiator fluid and make the whole situation worse?

Thanks, for the input! It's near midnight here, so I'll do some more tests tomorrow.

[Strawdawg]

As I stated originally, be sure you have relatively new coolant in the system as old fluid becomes acidic which greatly enhances electrolysis.   Or one can add an additive like RMI-25 or a similar lube/anti-precipitant additive.

[bandt]

Sorry, Little bit of a hyjack,

I don't remember seeing a firewall to block ground strap on any car. I have a 72 340 are they suppose to have the firewall ground??

Brian

[nqkjw]

Sorry, Little bit of a hyjack,

I don't remember seeing a firewall to block ground strap on any car. I have a 72 340 are they suppose to have the firewall ground??

Brian

Me either.
Was just putting it out there that they do in earthmoving machines with alloy radiators so it can't hurt?
I know I do with alloy radiators.

[MEK-Dangerfield]

You know, I have never done this test. My engine doesn't have that braided ground wire. As far as I know, the radiator is original.

I'll do the test soon out of curiosity.

[bandt]

Did they originally come with a body to block ground?