Mixing coolants

[r5gtt]

I've never used de-ionised water!  I've never seen dealers or indies use it either!  What is the reason for using it?  Just curious.

I believe the coolant already contains water conditioners, assorted other lubricants and rush inhibitors etc.

De-ionised water has been filtered to remove chemicals that could scale the metal surface. A good example of this would be looking down your kettle's heating element if you just used unfiltered tap water for a while. Brand new it would be shiny but over time the tap water's chemical properties such as calcium, chlorides and magnesium would dull out and scale the metal surface. You can imagine what this can do to the cooling system in our cars so it is preferable to use De-ionised water if you can to reduce the build up of this problem (I live in the Midlands where we have really hard tap water so it's a no-no for me).

Not all coolant are ready-mixed, some are concentrated and need dilution. I have a Mobil 1 Advanced Antifreeze (G12+) that needs diluting on application, just check the instructions, apply the right amount and you be good to go! 

the guys are right and if living in London the water is awful as for a young age I never liked this water and only recently found out why 

[grey golfster]

De-ionised water is not the same as distilled water, but in my experince either is good enough for engine cooling.
Just don't put that cr@p that they have in London, or other similarly "hard" water into your engine!

I use the condensate out of my dehumidifier,  there's plenty of that here at this time of year!

I recall you can buy deionised water in Tesco/asda (used in steam irons), probably as cheap as anywhere?

[pudding]

OK cool.

I've had VWs since 1990 and always used tap water, and yeah, it's the East Anglian rock hard variety that scales up a kettle in 3 weeks 

Over the years, the various blocks, heads and water pumps I've stripped down or worked on have never shown any signs of scaling up when using VW coolant.  I don't disbelieve it, just saying 

I'm pretty sure G13 will have some kind of water conditioners in it, since VW can't guarantee the water quality around the globe.  I bet there are some tribes in deepest Africa that use muddy water from wells in their engines!