corrosion of alloy radiators?

[oldcorollas]

So i was wondering...
you often hear of people having bad corrosion problems with their flashy new aluminium radiators, and it is often said there is "stray current" etc causing the problems..

How many of these radiators are still being connected with black rubber hoses?
Do these black rubber hoses contain "carbon black"?

it may be that the corrosion is due to galvanic corrosion
but not for the reasons people think (stray earth currents)

has anyone noticed a difference in corrosion when changing from black rubber to silicon hoses?

edit: i don't know if this actually happens... just postulating...

[river]

Hi,

Hmmm, maybe a gold or platinum radiator would be beneficial, if not a tad expensive!

I was under the impression that the new radiator cooling additives (the green stuff and the red one) where designed to minimise corrosion?

Also, would a sacrificial anode (like they have in hot water systems) be of any use, and save the radiator (or cylinder head) from corrision?

seeyuzz
river

[Z2TT]

Maybe when the radiator coolant isn't replaced when needed the anti-corrosion properties decrease over time?

[YLD-16L]

My aluminium JAR radiator is about 2.5 years old now and I just run standard black rubber radiator hoses and Toyota red coolant.

I took it out about a month ago when I was doing some work and the inside of it looks like new still.

[matty12]

I do this sort of stuff day in day out.Mixed coolants and stray current will give you the same readings when measured with a analogue multimeter.Nine times out of ten its mixed coolants and incorrect flushing methods.We use a maximum of 0.05 volts before we are happy with the vehicle to go out.

The rad should be rubber mount if possible and i only a small percetage of cases(very small)has a earth wire fixed anything.

Stary current normaly blacks header plates and will leave a white powder(i think it aluminium oxide) lining the tanks etc.

[oldcorollas]

0.05 volts between where and where?

I am wondering if the corrosion sometimes seen is actually due to more localised processes, rather than an electronic exchange between the radiator and the engine block?

[matty12]

when at operating temp ,drop the positive lead into coollant in rad,(careful not to touch the actual radiator)and neg onto battery and measure the reading.

every one says to use analogue and not a digital,but no-one can tell me the differnce.,The only thing i can think of the volts power the analogue and not a battery in the digital,i could be so wrong though.

[oldcorollas]

i guess if the multimeter is 0-12V, a reading of 0.05V is hard to measure, especially if there is a galvanic cell set up between the leads and the liquid.... (ie, you could be making a very weak battery between the coolant and the lead)

perhaps people say to use analogue because you can visually see the needle move, even if only a little bit...

but i wonder if people are measuring the correct thing... different multimeter probes (different materials) and different amounts of electrolyte in the coolant will all give different readings anyway...

edit, anyway the localised corrosion i am talking about, would be producing voltage between the surface of the rubber and the nearby aluminium, so checking the voltage between the coolant and battery has no bearing on that i would think?

in any case, the stray voltage you would be worried about, would be between the aluminium and the engine block, assuming they are electrically connected (which it will be if radiator does not have insulated mounts)... hmmmm

[eeeyan]

Not sure what grade this aluminium is in Radiators... however working for an aluminium supplier yes that white powder is aluminium oxide.. also when aluminium is up against steel the aluminium acts like a sacrifical anode and will corrode in place of the steel dont ask me the science exactly it just does.

we get it all the time people come in after a year and say my gates slats are dissapearing and they have them screwed to steel...

Also aluminium whilst FAR better than steel for corrosion resistance does have its flaws. Specifically if water is flowing through or over ally its fine for corrosion but if water "sits" on the aluminium it corrodes quite quickly at least thats what happens with our warehouse stock. Anodising or powder coating your aluminium will correct this.

[Z2TT]

On the subject of anodizing, the black alloy radiators are ones that are anodized I assume, so would it be better to get a black alloy one as it wont corrode as fast (on the outside) that quick when constantly driven in harsh weather?, compared to a silver one?

Thanks.

[oldcorollas]

eeyan, that link above has a bti more info if you are after some.

aluminium can be bolted to steel, but it is better if there is a large area of aluminium in contact with the steel AND in contact with water... small area of wet alloy = unhappy alloy

Z2TT, anodised is anodised. of course there are different qualities.
black will make no difference the thermal loss because the actual aluminium oxide has higher thermal radiativity than the black pigment...

as long as the aluminium is anodised it will have same protection against corrosion, regardless of colour.

you might find many black radiators are just painted...

[eeeyan]

Oldrolla's is probably right about them being painted anodising is only about on average a 10-25um layer and it can be any sort of colour really clear, bronze, black, white, gold, champagne its just for looks though the colour the coating is the same.

i'm not sure how a radiator/intercooler once fully made would go getting anodised getting the tanks done separate to the "grill" would be the way to go i would have thought.

[Q-Authority]

FYI: on painting an aluminum radiator/intercooler, etc.

I have done a ton of web searching on this recently and have found the following, though I don't, of course expect it to be the last word on the subject, and don't sue if my memory isn't perfect.

What you need to consider, when painting/coating, a radiator, etc. is the emissivity rating of the material used to coat the object, and the emissivity rating of the material to be painted/coated. Emissivity is the ability of an object to emit energy by radiation. Not to be confused with heat conductivity, which is completely different.

It turns out that aluminum, while it conducts heat very well, is not the best when it comes to shedding that heat. It actually only has about a .15 - .2 emissivity rating, compared to a 1.0 rating, which would be ideal. And aluminum oxide only fares slightly better at around .25 or so. I have often seen posts stating that aluminum oxide is better than that, but I eventually found a number of engineering sites that showed its rating is only in the .25 area.

Now, while black color, for a good emissivity coating, is not absolutely necessary, it is certainly more popular, and apparently for good reason. The color black, while it does capture heat more quickly than most other colors, also releases heat much more quickly. Say that you left two wrenches lying out in the sun, a black one and a chrome one. The black one would heat up much faster than the chrome one, but once they are both up to a sizzling temperature, take both of them into the shade, and check their temperatures as they drop. The black wrench will cool off much faster than the chrome one.

Most engineeringing emissivity rating's charts that I have seen generally list black coatings, in general, up in the .7 - .9 emissivity rating, which is much better than natural aluminum or aluminum oxide. However, the make-up of the coating does make a difference. Apparently special materials can be added to a coating to help transfer the heat better from the surface coated and more quickly shed it as well.

Also, it appears that annodizing in general has a relatively decent emissivity rating (around .7 - .9), although it also appears that the annodizing will degrade over time, much more quickly than your general specialty coating, at least when extreme temperatures are involved, and you will eventually lose some of the heating shedding ability.

Well, that's what I have picked up on it so far, and I plan to have a new aluminum radiater coated with a special heat dispersant, along with a new a/c radiator/condensor, unless I see something really contrary to all of this.

[river]

Hi,

But, in general, do automobile manufacturers annodize or paint their radiators, or air-con condensors? Same with intercoolers.

If not, then perhaps the difference between annodized/painted or left untouched is not significant to warrant the cost.

seeyuzz
river

[trdee]

pretty much every factory radiator i have ever seen has been painted black?

as for the corrosion thing, galvanic action could definately be a possibility, specially when you are bolting up alloys with steel and whatnot (havent read about this shit for aaaaaaaages)