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MG MGA - rust in cooling water

Twice recently I've replaced the water in my radiator and have been surprised to see how much rust there was in it - totally brown, no trace of any clear water. I'm using about 2 pints antifreeze that is approx 20% and I thought that it should stop corrosion but obviously not. Should I raise the 5 to say 30 or 40%?
J H Cole

Hi JH, Sounds as though your whole system needs flushing out - obviously some trapped rust deposits in the block somewhere, which will be unaffected by antifreeze.
Cam Cunningham

JH,
I'm running a 50% anitfreeze mixture and still experience a similar problem. The engine was flushed and radiator re-cored this spring, but the "problem" still occurred. I don't think there's any way to entirely stop it.
Cheers,
GTF
G T Foster

JH
I am running 100% premixed Castrol coolant with rust inhibitor, it starts a kind of yellow color and seems to have remained that way. I have however flushed the block when I got a new radiator last year. It is quite surprising how much crud comes out when you flow water backwards through the engine!!
Water will always breed rust unless there is an inhibitor present.

Neil
Neil Purves

I always use 50/50 glycol and water mix, replaced every couple of years, and it sill rusts somewhat. Last year I replaced a clogged heater valve that was no more than 7 years old (perhaps less in service). The engine block was mechanically routed to remove all rust and sediment from the water jacket several years ago, but the rust persists anyway. I just had my radiator recored again, but I have to give that credit for lasting about 20 years and 200,000 miles.
Barney Gaylord

JH, does your car have a heater? If so, have you tried flushing it? Every heater core I've ever taken out was filled with rusty silt.
Mark J Michalak

Thanks for the responses, I think I will go to 50/50 antifreeze mixture and then add some water wetter to compensate for the antifreeze reducing the thermal conductivity (right term?) with the metal. I will also try back flushing that I've only read about. I assume that you connect a hose up to the engine block tap but do you open the bottom radiator valve as well as the top cap? MJ I've got a heater that I will also independently try to flush and see what comes out. Is there any mileage in using collected rainwater rather than tap water. I remember at school the experiment of putting shiny nails in distilled water - no rust!
J H Cole

Mentioning using distilled or even de-ionised water in a cooling system is a very good way to start an argument as there are some very strong opinions out there. My opinion, for what it's worth, is:-

a) it's a waste of money.
b) it is just possibly actually harmful

First do not confuse rain water with purified water, rain water picks up all sorts of rubbish as it falls through the air and is actually slightly acidic by dissolving some Carbon Dioxide. I also think you have remembered your school days wrongly. The experiment with nails shows that air (oxygen) is required to form rust. Have a look at http://www.practicalchemistry.org/experiments/the-causes-of-rusting,209,EX.html .

Some people advocate going to the length of using de-ionised water. Before you try this, I can only advise speaking to someone who uses the stuff industrially. De-ionised water is highly reactive, it has had all its metal ions stripped out and is quite keen to put them back.

When you consider that the cooling water is both hot and in contact with iron, aluminium, copper, zinc and probably several other metals, the electro chemical reactions that go on will be quite remarkable, so no wonder it turns a bit discoloured.

Flushing is required because rust has the property of not sticking well to the base iron and so flakes off into the water. (The oxide layer on aluminium for example, by contrast is very well attached.) It is the flakes of rust, some very small, that accumulate in odd corners of the cooling system (with a special attraction it seems to the passage way near the block drain tap) that you remove by flushing. To flush the radiator properly, remove it, turn it upside down and put a hosepipe in the bottom
pipe. Run till the water is clear shaking the rad every so often. While you've got the hoses off you can do the same to the block although shaking it is a lot harder. As an alternative there are also plenty of cooling system cleaning chemicals out there which are worth trying.
Malcolm Asquith

This issue is a "hot button" with me. Without citing professional credentials, I'm a chemist who has studied surfaces and corrosion for longer than I care to admit. There is simply no practical difference in the solubility of metal ions related to automotive cooling systems in distilled water and tap water. The idea behind "hungry water" is largely an urban legend worthy of "Myth Busters." Depending on pH, hard water can have a near saturation of calcium and/or magnesium ions, but still will permit corrosion of iron at about the same rate as distilled water with similar conductivity bought about by different adventitious electrolytes. Anions, including sulfur and halide, when present in water can greatly accelerate dissolution of metals - far beyond any corrosiion rate achievable with distilled water. Using distilled water in automotive cooling systems is neither beneficial or detrimental, only inconvenient and more expensive.

Radiator flushing usually is performed at elevated temperatures with oxalic acid. (Pour the stuff in, run the engine and flush with clean water.) Sometimes, the flushing hose is connected at the radiator return to "back flush" the system. Sometimes fresh water is just added to the radiator with the tap open or heater hose removed until the water runs clear. Some people remove the thermostat during the flushing process.

Modern antifreeze solutions have rust inhibitors added. Phosphate used to be used extensively, and is still the best for iron. However, with more aluminum used in engines, other, often organically based, additives are being used.

The B-series engines are very difficult to flush completely. Anyone who has tried to use the block drain knows that despite coolant circulating in the block, rust will build up that blocks the drain tap, as well as the threaded boss passage. Most flushing is performed for too short a period of time to completely dissolve such relatively large accumulations of compacted rust particles. That is why the rust often reappears after flushing. It's not because the block is continuing to rust, only that the deposits are loosening over time since they are not being replenished with fresh material.


Steve
Steve Brandt

SB, in reading my antifreeze bottle it says it has anti corrosion properties but only contains 'ethylene glycol', is this the inhibitor if not where are the other goodies? Should we be adding extra inhibitors?
NP I checked out your Castrol Coolant since it sounded good but it turns out to be only 50% antifreeze with 50% deionized water. With the above comments in mind it may not necessarily be the best solution but I'm beginning to see this how whole subject is quite contentious.
J H Cole

Ethylene glycol is the actual chemical compound used as antifreeze. When added to water, it both raises the boiling point and lowers the freezing point of water. It's not unusual for antifreeze containers not to spell out the corrosion inhibitors used. Just stating that the mix contains them seems to be enough to satisfy government ingredient requirements for these products. When changed regularly, about every two years and/or 25k miles here is really no need add additional compounds. There are also "permanent" antifreezes on the market now, but I have not made a close inspection of their composition. Simply "Googling" "antifreeze" will open up a wealth of information, if you want the details.

By the way, the "pre-mixed" antifreeze is just ethylene glycol that has been diluted for immediate use out of the bottle. Excluding the extra water, it is exactly the same chemistry as in the straight antifreeze solutions from the same company. Since the price of these pre-diluted mixtures is about the same as the straight antifreeze, you wind up actually paying about 2X the price for the active ingredients if you go this convenience route. It's all about the marketing.

Steve
Steve Brandt

This thread was discussed between 18/08/2008 and 19/08/2008

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