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Aluminium engine radiator flushing - tap or deionised water?


 
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iam_TJ
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PostPosted: Wed Sep 23, 2020 21:25    Post subject: Aluminium engine radiator flushing - tap or deionised water? Reply with quote

I'm about to replace the coolant in the 6G74 3.5 GDi engine. There's signs of rust in the water so I intend to flush the system. I've bought a bottle of Holts SpeedFlush.

The instructions on the bottle are slightly obtuse since it tells you to drain and flush the system before adding SpeedFlush! At first read it sounds like it'd be pointless to add SpeedFlush if the engine has already been flushed!

HOWEVER, aside from my being pedantic, I'm wondering whether it is OK to use tap-water to do the initial flush after draining to rinse out the worst of the contaminants before adding SpeedFlush and deionised water and running the engine and heaters as recommended ?

I've read various arguments for and against the use of tap water for flushing. Logic would suggest it won't do any harm since:
    * it won't be in for long
    * won't be used as a coolant so shouldn't result in heat-related chemical reactions
    * will be almost completely diluted and flushed out by the following SpeedFlush treatment
    * any minerals remaining will be neutralised when the 50/50 coolant and deionized water is added

Anyone got knowledge or links to authoritative information on flushing aluminium engines with (UK) mains-supplied tap water?
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alanymarce
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PostPosted: Thu Sep 24, 2020 16:38    Post subject: Reply with quote

I think that it depends on your tap water. Some places have mains water which has a lot of stuff added (I don't plan to get into whether this is good or bad) and also hardness levels vary from one area to another. If you have relatively "pure" mains water then I don't see a problem using it.

Similarly if you have well water, it depends on the same things.
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peteinchad
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PostPosted: Thu Sep 24, 2020 17:47    Post subject: Reply with quote

I can't see any problem, I have always flushed out all my engines with tap water and Holt's RadFlush - and I have always flushed my cooling systems every year. Using a hose pipe is the only way to get enough pressure to give it a good flush - so tap water is the only option.

I refill with distilled or deionised water and a good quality antifreeze at a 50% mix.

Any potential problems caused by the small amount of tap water remaining will be nullified by the anti corrosion additives in the antifreeze.
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iam_TJ
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PostPosted: Fri Sep 25, 2020 8:39    Post subject: Reply with quote

That was my analysis as well. One issue where my research suggests you need to be careful:
peteinchad wrote:

I refill with distilled or deionised water and a good quality antifreeze at a 50% mix.

According to several authoritative sources (coolant manufacturers specifications) there is a big difference between Distilled and Deionised water in terms of what is removed, and we should use Deionised water, not Distilled. E.g:

Comma Super Longlife Red - Antifreeze see the technical data sheet "Dilute with de-ionised water in accordance with the
vehicle manufacturer's instructions."

Why You Should Never Use Distilled Water in Your Cooling System

The Difference Between Deionized Water and Distilled Water
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peteinchad
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PostPosted: Fri Sep 25, 2020 12:02    Post subject: Reply with quote

Maybe technically those two links are correct but in real life all you are trying to do is stop limescale being deposited in the cooling system.

Deionised and distilled will both stop the deposition.

The free ions in distilled water will soon dissipate as the water in the cooling system will absorb impurities that are present in the system no matter how well you flush it, and adding the antifreeze / coolant will also affect the ion balance whichever water you use.

I have used both - in engines that are all aluminium or have aluminium cylinder heads and I have never seen any detrimental effects. That means that any reaction with distilled water is either extremely slow or it doesn't cause any adverse effects.

I have always changed coolant yearly - using RadFlush or similar and I think that the chemical used for flushing is more likely to cause damage - but it is really the only was to remove any contaminants from the system.

I have worked in a few laboratories in the past and distilled water was always preferred - but Deionised was used as a substitute if necessary.

It is easy to overthink this subject - I think that any adverse effects will take so long to show that it is not a problem, the bodywork will have rusted to dust in the time it takes for the engine to suffer from distilled or deionised water.

Just make sure you don't use tap water - or like my dad who used rainwater because he reckoned it was pure water .... but that was 50/60 years ago and many people did not know much science.
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iam_TJ
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PostPosted: Fri Sep 25, 2020 21:55    Post subject: Reply with quote

Agreed about over-thinking - I was more interested in resolving the various opinions on what (not) to use and the sometimes nebulous reasoning. In this arena there are too many armchair professors and it is hard to recognise fact from fiction!
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