Deionised, or from the tap? - Robert Fleming
About to replace the anti-freeze in the Golf.

Is it worth using deionised water? The olde Polo seems happy enough on chlorinated fare, but the Golf's cooling system has suffered under previous owners, and looks a little rusty coloured.

Rob F
Deionised, or from the tap? - Rich Mixture
I've pondered this one myself Rob. SWMBO's Corolla handbook specifies deionised water for the coolant, but I was in a hurry when I changed it so I used tap. Next time I think I'll definitely use deionised as it seems like a sensible thing to do, given the nominal cost of 5 litres of deionised water at Halfords. We live in a very hard water area and I guess the less limescale you stick into your rad, block and heater the less likely it is to end up looking like my kettle (or the fact that washing machines seem to have an average lifespan of about 14 months in our house - due, according to the repairmen to excessive scaling. Good job they're insured!).

Deionised, or from the tap? - blank

Chlorine is not a problem. Hardness deposition (scale formation)is a BIG problem. So is corrosion.

To prevent scaling, use deionised, or at least soft, water. When I lived in Lancashire I had no problems useing tap water. Now I am in Kent I use deionised. If your tap water is hard at all, used deionised.

To prevent corrosion, use a decent quality coolant additive, commonly known as antifreeze, but it does much more than prevent freezing. It also prevents corrosion. Change it regularly, as recommended.

In short, to answer your question, yes.
Deionised, or from the tap? - lauriew
Some car makers sell their own brand coolant ready-mixed. Have you checked with VW.
Deionised, or from the tap? - bazza
Andy S is correct. Tap water is not the culprit, it is lack of coolant changes. I would reverse flush your car's system and re-fill with a strong antifreeze solution, buy the best quality as well. Unless you live in a very hard water area, tap water will be fine. Then if you keep the car, change the coolant regularly, probably every 2 years minimum. Also, if you have to top up, use the same anti-freeze blend, not water.
Deionised, or from the tap? - Onetap
Use anti-freeze pre-mixed with deionized water. Don?t use plain de-ionized water, it?s aggressive and will attack the engine parts. Plain tap water would be preferable.

Scale shouldn?t be a major problem with tap water, unless you?re topping up the system continually. Water in the London area has about 250 ppm (or mg/l) of hardness, so 5 litres would introduce about 1.25 gms into your cooling system. The dissolved solids are a problem, in that they ?consume? some of the corrosion inhibitors in the anti-freeze mixture, reducing the life of the coolant.

Most car anti-freeze mixtures contain mono-ethylene glycol. In the presence of heat and oxygen, this will oxidize into acidic compounds (sorry, don?t know the formulae). When the corrosion inhibitors have been exhausted, the solution will then start to corrode the metal components in contact with the coolant. Head gasket failure is, I think, the usual result. The only prevention is regular flushing and renewal of of the coolant. The recommended interval is about 2 or 3 years.
Deionised, or from the tap? - Cyd
"Don’t use plain de-ionized water, it’s aggressive and will attack the engine parts."

Can you illucidate, please.
Deionised, or from the tap? - M.M
I'd like to know too Cyd. If afm is right all the "caring" garages around me are wasting their time buying de-ionised water in 25lit tubs and mixing it with glycol.

Deionised, or from the tap? - Onetap
"If afm is right all the "caring" garages around me are wasting their time buying de-ionised water..."

No, that's the right way to do it.

Sorry if I didn't make myself clear. What I meant was that you shouldn't use neat de-ionized water, it is corrosive. It will not remain de-ionized, but will strip ions from the cooling system components.

De-ionized water systems are generally piped in plastic, ABS or uPVC for this reason. It can corrode stainless steel.

De-ionized water mixed with an anti-freeze mixture has got loads of ions in the solution, it is not corrosive and is what you should be using.

Hope that's as clear as DI water.
Deionised, or from the tap? - Andrew-T
Sorry, afm - I'm still not convinced that DI water is 'corrosive' just because it contains no ions. When fresh it should have a pH of 7 (i.e.neither acid nor alkaline) and should do no damage to anything. However I doubt whether you can stop it absorbing air (i.e.oxygen) which will start the corrosion process. The important thing is to add corrosion inhibitors (in the antifreeze) and avoid including mild alkalies in the form of calcium ions in hard water.
Deionised, or from the tap? - Onetap
Isn't that what I was saying, pre-mix it with the anti-freeze? I might, in an emergency use plain tap water in a cooling system, but I wouldn't use plain DI water.

I don't know why it's more corrosive but, believe me or not, it is. It may be because it can absorb more oxygen or carbon dioxide than ordinary water. The effect of a DI water leak onto any metal can be costly, possibly because it's assumed it's 'only water'. Since we all seem to agree that we wouldn't use it neat, it's not really relevant. It would certainly perforate most of the usual metal alloys (stainless, brass, bronze, steel, copper) in a DI generation system, but this involves a continuous flow of fresh DI water and not a single charge of 7 or 8 litres, as in a car.

I'm not going to monopolise the thread any more, we've talked it to death. Thank you all, interesting discussion.

Deionised, or from the tap? - Cyd
Flush the cooling system with a cleaner, such as Holts Radflush. Then fill with best quality antifreeze and deionised water. The water only costs a few ££s and you will prevent further limescale deposits.
Deionised, or from the tap? - Mondaywoe
You can buy ready mixed stuff in accessory shops.I filled my Mum's Clio with this a couple of years ago. I think it was 'Comma'. I used to run Renaults in the past aND I always bought the ready mixed stuff (Renault's own) It was a bit pricey, but I never had any problems with radiators hoses, pumps, head gaskets etc. The Comma version is cheaper and claims to be long lasting. Must check, but I think they said to leave it 3 years.
Deionised, or from the tap? - DGW
Are there any drawbacks to using water collected from a condenser tumble dryer?
Deionised, or from the tap? - Dwight Van Driver
......or a room dehumififier?

Deionised, or from the tap? - Dwight Van Driver
I Must learn to spell x 100 (Dehumidifier)

Deionised, or from the tap? - Phil I
Not to worry DVD. I think this may be the only forum on the web with grammar and spelling monitors.!!! :-)

Phil I
Deionised, or from the tap? - Onetap
It's got lint and dust in it and any soluble gases it may have picked up from your rooms or from your laundry. Try it if you like a gamble, I wouldn't. Why would you bother? DI water can't be that expensive, can it? I have access to a DI water system so don't often buy itn.

I regularly read posts on a US heating forun ( In rural areas, the water supply will often be drawn from a well, and the water can be unsuitable for filling a heating system. They also have many heating systems containing anti-freeze, because of their severe winters (usually mono-propylene glycol, non-toxic). In both instances, they would buy DI water and the cost mentioned was about 8c per US gallon.

We'd expect to pay much more for the same product.

Incidentally, car anti-freeze is very toxic. It will kill 100% of everything. Does anyone know how it should be disposed of other than letting it run into the surface water drains and so the rivers?
Deionised, or from the tap? - Cyd
Used antifreeze should be poured down the toilet and flushed away. It will them be dealt with via the sewerage system. Surface drains go straight to the rivers, so it should not be poured down them.
Deionised, or from the tap? - Onetap
No. It is toxic chemical waste. It should not be tipped into any drain. Most drained anti-freeze is drained onto the street, from where it makes it?s way into the surface water drains, the rivers and the sea. It could be most easily re-cycled or destroyed if it wasn?t diluted with sewage and industrial effluent.

At a sewage plant it will destroy some of the bacteria which are cultivated to digest the sewage.

Does anyone know of a means of responsibly disposing of small quantities of anti-freeze? I?ve paid a specialist waste disposal contractor in the past, but that was for several thousand litres. I?ve used small quantities to treat my garden fences as a wood preservative.
Deionised, or from the tap? - CMark {P}
Actually, afm, I am 100% with Cyd.

Ethylene glycol is very toxic, as you say, so never tip it down street drains but it is safe to pour single vehicle quantities down the toilet as the sewage system will deal with it properly.

In fact it says on my spare bottle of US made antifreeze/ coolant concentrate "we recommend disposal in sanitary systems".

You can get antifreeze which is non-toxic - propylene glycol.

Also never use softened water in a cooling system as it substitutes s**ium salts for calcium. This s**ium is very corrosive to all metal surfaces and will tend to negate the corrosion inhibitor additives present in the coolant.

I always use de-ionised water when mixing with coolant concentrate. Also now I put it in the screen wash bottle.

Deionised, or from the tap? - Robert Fleming
Well thanks people - received wisdom is to use deionised, which I did (at £3.25 for 5 litres from Halfords, which was a little steep for my liking).

Also I used G11 (VW coolant), which I felt was worth paying for, as its green sibling G12 (no longer available, so I'm told) has prevented even a whiff of corrosion in the venerable Polo, which has a similar alloy head/iron block setup (I think).

After sneering at the price of the G11 at the silver-plated VW dealer, they gave me 12.5% off. So they can damn well do the same if I get a genuine exhaust from them....


Rob F
Deionised, or from the tap? - blank
Is VWG11 the lurid pink stuff? I'd love to know what they put in it to send it that beautiful almost luminescent shade!!

Deionised, or from the tap? - nick
Rainwater is ok, buy a water butt.
Deionised, or from the tap? - steve52
I have access to Double Distilled water from a laboratory. What is the recomendation or otherwise for using this mixed with antifreeze? (How does it know if it's antifreeze or summer coolant!?)
Deionised, or from the tap? - Onetap
Chemically, it's about the same as de-ionized. Usually the water goes through a de-ionization process (softening, RO, CDI) which takes out virtually all the dissolved solids. Distillation is required to kill off any organisms in the water.

PS I still don't agree with tipping MEG down the drains, the water supplier indicated it's very unwelcome. It seems no-one knows of a more environmentally friendly way to get rid of it.

See also;
Deionised, or from the tap? - Cyd
...PS I still don't agree with tipping MEG down the drains... I said toilet not drains. And...

I knew I got the disposal advice from a reputable source, it just took me ages to remember where.

On the back of a recently purchased bottle of Halfords Advanced Protection Anti-Freeze it says..."Used anti-freeze: dispose via sink or toilet and flush copiously with water. Do not put down surface drains."...

If you still disagree, take it up with Halfords and let us know their response.
Deionised, or from the tap? - Onetap
Surface water drains go into the rivers, foul water drains connect to the sewage system and n'er the twain should meet. I was told that the water suppliers, who also operate the sewage system, didn't want any mono-ethylene glycol tipped down any drains. It was not welcome at their sewage plant. The proper disposal method was to dispose as chemical waste. Isn't your toilet connected to a drain pipe?

I'm not interested in Halford's expert opinions. Should I follow the advice on the back of a Halford's bottle, or that of a chemist employed by a water board? Oooh, hard choice, that.

A lethal dose for a child/small animal is probably about a tablespoonful, so I think it's probably inadvisable to put it into a sewage system. A large proportion of the liquid waste is re-cycled back into the drinking water supply. Waste anti-freeze probably has some value and could be recycled. There is probably a much larger cost in neutralising it once it's in the sewage.
Deionised, or from the tap? - Onetap
As stated below, rather than dispose of it, it would be most sensible if the manufacturers were obliged to list the corrosion inhibitors and recommend suitable test kits and inhibitor top-up solutions.
Deionised, or from the tap? - blank
I hesitate to disagree with you, because you have written a lot of sense on this thread and I suppose I don't actually disagree with you. Let me explain!

1 - Some people change coolant in their cars. Usually one or two cars, perhaps every couple of years. I guess, only a guess, that 90% of the coolant removed is dropped into a surface drain. This is because the 90% don't know any better or can't be bothered doing anything else with it. This coolant will cause environmental damage in small water courses where it will inevitable end up fairly soon after dumping.
2 - There is no chance (IMO) of convincing any significant proportion of the aforementioned 90% to pay a contractor to dispose of their toxic waste for them.
3- With a bit of effort, there is a possibility that some of the above 90% will flush waste coolant down the toilet or sink.
4 - It is better for toxic waste to be hugely diluted, treated by a 3-stage effluent treatment plan then discharged to a large river of the sea.

I'm with Cyd and Halfords I'm afraid, though of course you are right really!

Deionised, or from the tap? - Onetap
Why, thank you, kind sir! I'm not disagreeing with anyone, really. It is, of course, preferable to tip it into the sewerage system rather than the surface water drains. My question was whether anyone knew of a better method of disposing of it. The answer seems to be a resounding silence.

Some years ago, many of your 90% probably tipped their waste oil into the road-side drains. Now most local councils provide re-cycling tanks and most people, but not all, don't tip oil into drains. Similarly, many local councils collect scrap cars free of charge, because it costs them less than collecting the car after the joy-riders, vandals and arsonists have made use of it. I wonder what the hidden, environmental costs of anti-freeze disposal via the sewerage system are, and whether the costs of providing re-cycling tanks could be justified. I don't know the answer.

Deionised, or from the tap? - John F
Absolutely. The tap on a butt is a few inches from the bottom, so very few contaminants which will either float or sink. And never change it. Oxygen is required for corrosion/rusting, and once the oxygen in the water has been used up there will be no more corrosion.

I saved the coolant in my 1980 TR7 when I changed the water pump last year [bearing, not corrosion failure] - the rad, heater element, etc are original and the head has never been off.

The antifreeze doesn't go off, either - I tested a sample in the freezer. I know of know scientific [as opposed to commercial] reason for changing coolant every 2yrs - you just introduce more oxygen.

Deionised, or from the tap? - Onetap
My earlier reply was in response to the query about using distilled water.

Anti-freeze does, most definitely, go off; see previous responses.

It is good practice to keep the water in a heating system, but with heating systems you should be adding oxygen scavenging chemicals to remove the any absorbed oxygen.

Car radiator hoses are usually permeable to oxygen, and the coolant will absorb more oxygen on every trip to the expansion/filler bottle. You need to change the coolant every 2 or 3 years.
Deionised, or from the tap? - blank
Just to add to afm's post, correctly I hope! It's the corrosion inhibitors that go off, rather than the freezing-prevention parts of the coolant additive. That's why it should be replaced regularly.
With a TR7 (if it's got and iron head and block) corrosion is unlikely to be a problem, but with aluminium block, head or both it could become a serious problem in little time.

Deionised, or from the tap? - Onetap
True, and when the corrosion inhibitors have expired, the coolant gradually becomes more acidic. It would be interesting if John F got hold of some litmus paper and checked the pH of his TR7 coolant.

I think bad coolant might also attack the radiator through galvanic corrosion, I'm not sure whether it's the copper or iron that corrodes without looking it up.

Deionised, or from the tap? - John F
Admittedly it is over 30yrs since I got A level chemistry but I fail to see how a chemical like ethylene glycol can 'go off' if it is not subjected to other chemicals or a digestive process of some sort. As I said, a sample of my fairly ancient coolant remained liquid in my deep freeze.

As far as 'corrosion inhibition' is concerned, if you take steps to prevent the incursion of oxygen by not changing the water frequently, corrosion will only occur very slowly. I agree that there is a theoretical possibility of perfusion across the flexible tubing but this is a very tiny effect. All the tubing on my TR7 is original and in good condition - a credit to modern materials.

Other cars I have/have had have travelled 190,000 145,000 and 215,000 with no incontinence/head problems following this policy. [there is a lot of dogma and kid-ology in business and the motor trade is no exception].
Deionised, or from the tap? - RichardW

There's a really good aritcle on the web somewhere that explains why you MUST change the coolant regularly, and particularly on iron / alloy engines where electrolytic corrosion makes matter worse. Don't know the URL off hand though.

Basically, there are 2 components to 'anti-freeze' - the antifeeze part (MEG or similar) and the corrosion inhibitor parts. What happens is that over time with the heat from the engine the glycol breaks down and forms acidic components. These are dealt with by the 'buffers' in the antifeeze which maintain the pH at around 10. Once these buffers are used up, the pH begins to fall, and you get acid promoted corrosion. 2 tests then are really required to see if the antifreeze is any good - the freezer test, plus a pH test. Anything below say pH 8.5 would indicate a change is required.

The article also covers the Organic Acid Technology antifreezes which are much longer lasting - typically 5 years - and generally the orange / pink fluids seen in most new cars. OAT and MEG should not be mixed together as this reduces the protection down to the levels in the OAT.

I believe corrosion is more of an issue in modern cars with multi metal engines, and minimum thickness walls - rather than 30 year old designs which were 'substantial' by today's standards!

Deionised, or from the tap? - Andy P
Since when has deionised water been "corrosive" and "aggressive"? To me, hydrochloric acid is "corrosive" and "aggressive". Deionised water is only weakly acidic due to dissolved carbon dioxide forming carbonic acid, but this happens with water of any kind.

The process of forming deionised water involves removing anything that can ionise - acids, alkalis, metal salts etc, so as produced, deionised water is not corrosive.

Deionised, or from the tap? - RichardW
Hmm, that post was supposed to come out in the middle, where it would have been more in context and I wouldn't have repeated a lot of what had already been said that I hadn't read!

Anyway, here's the URL I mentioned:

Interesting reading (OK, I'm a bit of tech nut!)

Deionised, or from the tap? - John F
Thanks, Richard, the 'babcox' is v interesting if slightly contradictory.

'the additives [inorganic salts] form a protective coating'. Good.

'the higher the percentage of minerals and salts, the better it conducts electricity' - resulting in electrolytic corrosion. Not so good!

'ethylene glycol can be recycled'. Agreed!

So it would seem the best thing to do is to flush well, add a good quality 50/50 mix with pure butt water so the additives leave the solution and form a protective coating leaving a non-conducting and eventually virtual oxygen-free fluid.....and forget about it for the life of the system.
Deionised, or from the tap? - Onetap
In this thread about coolant, three different types of water were mentioned.

Softened water is more aggressive/corrosive than tap water. It can perforate copper pipes or metal storage tanks in 10 or 15 years. De-ionized water is more aggressive/corrosive yet. It will leach ions, i.e., dissolve metal, from any metal components that it contacts. It?s probably only capable of corroding something of the order of 0.1 grammes per litre but, for water, it?s fairly aggressive stuff. It is nowhere near as corrosive as hydrochloric acid, but no-ones suggesting using hydrochloric acid as a coolant.

With a closed loop heating system, it is good practice to keep the water in the system, The dissolved oxygen will mostly come out of solution on first heating. However, when in use, the system water can absorb oxygen, e.g., from the exposed water surface in an expansion tank, or from a leak, if the pressure at that point is below atmospheric. It is usual to add oxygen scavenging chemicals, typically s**ium sulphite, and to carry out regular tests to ensure the concentration remains above 200 ppm, I think. If regular top-ups are required, it indicates an oxygen problem.

It is also good practice to maintain the pH at around 9 or 10 (alkaline). This will stop galvanic corrosion between dissimilar metals.

Car anti-freeze contains glycols, which will, in the presence of oxygen and heat, oxidize into acidic compounds. I don?t recall the formula; I?m an engineer and not a chemist. I?ve got it written down at work, if you?re that interested. When sufficient acid has been formed, all the corrosion inhibitors will have been consumed, the coolant becomes acidic and galvanic corrosion begins.

The problem is that most plastics or flexible hoses are permeable to oxygen. Plastic pipes are used in heating systems ( usually PEX, cross-linked polyethylene) but the pipe should have an oxygen barrier. There were major problems with many of the early under-floor heating systems caused by oxygen absorption through the pipe walls, causing corrosion of the metal components. Since car cooling systems have a large amount of flexible ?rubber? hoses, the coolant will be absorbing oxygen all the time. Not a lot of oxygen, but enough to turn the coolant bad in 2 or 3 years.

As stated in the Babcox site "To ensure that coolant remains alkaline for a reasonable length of time, there must be enough corrosion inhibitor to neutralize the acids formed from glycol degradation that occurs over time. This neutralizing capability is called "reserve alkalinity," and it varies depending on the type and quantity of additives used in a particular brand of antifreeze."

It would be much more sensible to monitor the concentration of the corrosion inhibitors, but since we don?t know what these are, and since suitable test kits aren?t commonly available, the only safeguard is to change the coolant regularly. OK?
Deionised, or from the tap? - Onetap
Having resolved not to hog this thread, I stumbled across a thread on an forum about removing small amounts (~1% concentraton) of antifreeze (ethylene glycol) from a wastewater recycling system.

These guys are usually knowledgeable. It seems settlement (100% solubility in water), ultrafiltration and distillation don?t work. However, a glycol recycling plant on a railway used reverse osmosis to separate the glycol from the water and the ?recycled glycol goes back into service. Works fine.? Presumably the concentration was much higher. See link below, but you have to register to access the forum.

I wonder how the sewage works neutralise the MEG? I?m sure they don?t put the liquid through RO before putting it into the drinking water. I think I?ll be putting a carbon filter in, a proper one, not the toy ones you see in the DIY stores. I think I?ll finance them glycol recycling tanks myself.

PS Re the DI water system that I?ve got access to; I installed it and maintained it for a while. I didn?t design it. I did get to re-design the bit that didn?t work properly.


Value my car