Radiator Corrosion Issues

[wrs 120]

Hoping someone can help with what has become an ongoing problem.

I installed an all ally radiator when I did my engine swap around 5 years ago. The first all Ally radiator lasted about 3 years and failed round the core tubes. The second lasted 1.5 years and the latest really expensive one from A1 Automotive Cooling has lasted 6 months.

All have failed round the core tubes. The first radiator showed no signs of electrolysis. The second and third did though, black on the inlet tank side and brown on the outlet tank side.

In all cases I've used distilled water 50%, BMW blue coolant 45% and Redline water wetter 5%. In between radiator replacements I've done a flush with distilled water. On the last replacement with the A1 radiator I measured voltages on the expansion tank and from the radiator metal to the engine earth. The expansion tank to engine voltage was -1.0mV ad the radiator metal to engine block was -600mV. All documentation I've found says to measure from the liquid in the expansion tank to engine earth and if this is very low (-1.0mV is pretty low) then everything should be ok. In my case it hasn't been ok.

The problem with the E36 M3 expansion tank setup is it's remotely mounted near the firewall. The only flooded connection through a hose is to the back of the head. The hose from the top of the radiator inlet side to the expansion tank isn't flooded with the engine off the therefore there won't be any electrical connection/conduction if the coolant is ionic in any way.

How therefore can I check the system to make sure electrolysis won't be an issue?

I suspect the -600mV from the radiator metal to engine earth is the problem. The radiator is well insulated from any metal and is isolated from the engine earth at all times. Even applying significant force in every direction to the radiator does not make the radiator move enough to touch ground metal. I would have though -600mV is ok as long as the coolant is non-conductive as there will be no current flow to create and electrolytic reaction. I'm at a loss to what to do and don't know what is or isn't an acceptable voltage and where the acceptable voltage should be from too. The usual guidelines for measuring the coolant voltage in the expansion tank to engine earth obviously don't work in my configuration.

So, how to solve this ongoing problem - any ideas?

Edited January 9, 2021 by wrs

[kwhelan 241]

you need to check and clean all your earth connections throughout the car, a decent earth and the current will pass through the metal and not find its way into the fluid in the first place, they recommend to test with engine off, again wit it running and by switching on accessories one by one looking for voltage spikes. Something like a big stereo amp in the boot not having a good grounding could be letting they stray currents out to find an easier path to the battery which in your case is the liquid which is conductive

anything over .3v will destroy a radiator, and some ali radiators come with a ground wire so you could try that

[wrs 120]

Thanks for the info. This morning I replaced the A1 radiator with a new standard BMW one from Silverdale. First I flushed 30L of distilled water through the engine. It was refilled with a generic inhibitor and distilled water.

Further investigation has come up with some interesting results:

Exp = Expansion tank to engine earth (E36 M3 style expansion tank mounted near the firewall)

Rad = Radiator Core to engine earth

Cur = the current flowing if radiator core shorted to the engine earth

Cold just after filling: Exp -100mV, Rad -1020mV, Cur -0.2mA

Hot Idle (92'C): Exp -152mV, Rad -1005mV, Cur -2.4mA

Hot 3000RPM (95'C, thermostat open, cooling fan running): -1060mV, Cur -2.5mA

Hot Idle (92'C) Headlights on: Exp -155mV, Rad -1005mV, Cur -2.4mA

Cranking (92'C): Exp -154mV, Rad -1025mV, Cur -2.4mA

Combination of any electrical loads (headlights, brake lights, heater, windows): Exp -150mV to -156mV, Rad -1005mV to -1025mV, Cur -2.4mA to -2.5mA

Battery earth disconnected (92'C): Exp -152mV, Rad -1005mV, Cur -2.4mA

It appears it's not bad earthing or significant change would be seen with loads and cranking. Also, since the radiator is fully insulated from the chassis it's electrically floating and has no current path to the engine earth or chassis. The inlet and outlet pipes both connect to the same aluminum housing so both hoses are at the same potential where they connect to the engine.

For there to be a -1V difference between the radiator core and the engine earth there has to be galvanic corrosion occurring. Maybe the generic inhibitor I've used is rubbish and is creating a reaction?

So, how to fix this. If the coolant was truly inert and non-conductive then there would be no voltage from the radiator core to the engine earth. How to fix this is unknown, any ideas?

[aja540i 1906]

Give the current an alternative path, earth the radiator properly so it doesn't need to travel through your coolant and take the radiator with it, really easy to do and run the tests again.

[M3AN 4016]

I've always used demineralised rather than distilled water based on various advice... distilled water isn't completely deionised whereas demineralised water is (or nearly completely at least), it helps that demineralised water is also less expensive.

I really have no idea about your specific problem but this might be something to consider?

[wrs 120]

There is no current right now, just a potential difference. Earthing the radiator will create current which would increase the rate of reaction. Right now I essentially just have a battery producing a voltage with no load on it. Earthing the radiator will provide a current path to discharge the battery. A battery in storage lasts much longer than one with current draw as the internal corrosion rate in the battery is slower.

I'm using Pure-Dew water, first de-mineralised then distilled, $7 for 10L so cheap as.

I'm going to try dumping the new coolant and just fill with distilled water to see if the voltage potential drops. Then I'll know for sure if it's galvanic. Just missed the shop shutting earlier - could have just tried Water Wetter and distilled water as another alternative to see what the difference is.

 

[wrs 120]

Have now drained and flushed the whole cooling system (including the block plug) three times with distilled water to remove almost all traces of the original coolant. Once filled with only distilled water the voltage between the expansion tank and engine earth (cold) is -56mV (was -100mV) and between the radiator core and engine earth is -305mV (was -1020mV) and the current if shorted is 0.0mA (was 0.2mA).

However, over 15 minutes the voltage kept slowly increasing between the radiator core and engine earth which suggests the distilled water is becoming ionic - possibly reacting with and absorbing the deposits inside the engine, hoses etc. After 15 minutes it went down to -420mV but is still decreasing...

It's possible residues from past corrosion issues are adding to the problem and stopping the inhibitor doing it's job.

Maybe a good flush solution needs run through the system to clean up the old deposits so the coolant can do its job correctly?

[wrs 120]

It's been a couple of hours now and the straight distilled water has settled out at -467mV.

I'm going to add inhibitor back in shortly as I don't like the idea of running straight water even for a few days while I try to sort out the issue.

I think I'm going to try a good flush product first then a thorough flush with distilled/demineralised water and then try the distilled water thing again to see if the voltage is lower and more stable. If it is then I'll put a 50/50 BMW blue coolant and distilled/demineralised water back in it. Not sure if I'll add water wetter back in at this stage.

Will post up the results after the flush and than again with the BMW blue coolant - can anyone recommend a really good flush product?

[kwhelan 241]

I still think you need to earth. you say there is no current from radiator but there possibly is, although the radiator is in rubber there is still possibly a measurable slight  connection to earth from oils or contaminants on the mounts or bolts. apparently its possible  even through the hoses if they are old and dirty inside it can't hurt to test after earthing the radiator anyway.

earths are measured in ohms, not every earth will have the same reading due to differing connections, its a bit like jumper leads not all being equal in there ability to transfer current

I don't think you can fully remove the current from the liquid so think your wasting time with all the flushes, having many different metals that the liquid is contacting is going to cause currents, liquid carrys a charge that needs to get back to the battery terminal, there is possibly a slight path through the radiator to earth that your tester isn't picking up, you need to be measuring the ohms from all your earths and radiator and you probably need a megger tester that applies a voltage as its testing not a simple probe tester.

earthing the radiator makes it 0 ohms or dead in the circuit

earths are a real science even in electrical gear especially audio gear but it shows as noise, BMW usually run earth circuits but there were earth points scattered around my e39 from taillights etc and wires that go brittle inside the boot lid flexi rubber hose can  cause all sorts of weird faults in e36

some people in custom cars earth the radiator, the cap and even fit an anode inside that is designed to rust away saving the radiator and is an easily replaceable part, a bit like they do on aluminum  boat propellers , you replace the anode not the prop.

does seem an odd fault but it doesn't happen that bad to all so it seems a bit more specific to your car, good luck

[wrs 120]

Thanks for your thoughts. I'm an electrical engineer specialising in power electronics so understand the electrical side of the problem well. I'm of the opinion earthing the radiator will make current where little to none exists now which will make the corrosion worse. BMW didn't earth bond the radiator for a reason.

Earthing the radiator will create electrolysis due to current flow. With no earth there will be a significantly slower chemical reaction that isn't accelerated by current flow.

With no hoses connected there's >10M ohms from the radiator core to the engine earth. The hoses are new silicone. With the hoses connected there's also >10M ohms. Once coolant is present there's a voltage so ohms cannot be measured. I'm pretty sure there's no leakage current to the engine earth from the radiator core except through the resistance of the coolant which cannot be avoided unless there's no coolant.

Earthing the radiator also exposes the system to potential electrolytic effects from bad earths. If the radiator is floating with M ohms of isolation then it's impossible for bad chassis earths to have any effect because the radiator is floating and moves with a potential relative to the engine earth, not the chassis earth. Even if the hoses are dirty and have some resistance this slightly bonds the radiator to the engine earth, not to the chassis so no other earthing issues to the chassis will have any effect. Even if there's a few hundred k ohms to the chassis this represents a few micro-amps max of leakage at the small voltages present.

Possibly the biggest issue is I cannot measure the voltage present in the coolant like all the documentation I've found to date says to. Every reference I've seen says to put the positive probe into the expansion tank in contact with the coolant but without touching the metal. This assumes the expansion tank is built into the radiator so the coolant is close to the radiator metal. In my case the expansion tank voltage is acceptable but it's not even connected to the radiator so measuring in the expansion tank does not give a proper result.

I'd be interested to know what other BMW owners have as a voltage when measured from the radiator core metal to the engine earth. If it's similar and there's no problems then I'm potentially barking up the wrong tree using this as a metric to know if it's good or bad (then what...).

[leichtbau 525]

Following along with interest, galvanic corrosion is an utter bastard to chase down. Don’t have anything specific to add, but I’ve had a couple of issues on steel hulled super yachts over the years where the culprit causing the corrosion was so far removed from the issue that I wouldn’t have believed if I hadn’t found it in the first place.

[dirtydoogle 383]

I would be constantly checking the alkalinity of your coolant during the testing. 

467mV sounds a bit high to me? I can have a look at some of my cars and see what they're doing

[wrs 120]

Thanks that would be great.

The measurement I'm interested in is from the aluminum on the head to the aluminum on the core of the radiator.

[dirtydoogle 383]

Right, I've had a look at my Hilux, Lexus, Corolla, e36 316, our work truck and Camry, all are below 100mV running

[wrs 120]

Thanks. Measured a mates 335 at work, -365mV running but cold.

This has an alloy block head and radiator.