Using Demineralised water to top up coolant level?

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michaelqian, Jan 5, 8:03am
Hi all. I have a 2003 BMW 530i. There is a slight coolant leak. I think it is at the top of the coolant expansion tank. Right now level is very low. Is it ok to use demineralised water to temporarily top it up until it's fixed! Thanks
pettal, Jan 5, 8:17am
yep .
johnf_456, Jan 5, 8:18am
Sure is
robbo36, Jan 5, 8:48am
Be careful using demineralised water long term in a engines cooling system, as it is very mineral hungry and aggressive. As you can imagine with demineralised water it is looking for minerals and will strip them from whatever it comes into contact with, especially metals such as copper and aluminium.
a.woodrow, Jan 5, 8:50am
Nothing wrong with using regular old water also
michaelqian, Jan 5, 9:02am
So is it actually better to just use tap water!
johnf_456, Jan 5, 9:04am
Just use tap water
michaelqian, Jan 5, 9:32am
Probably a pedantic question, since I'm always extremely careful by nature. The density of engine coolant is 1.11 kg/m3, while that of water is 1.00 kg/m3. Would mixing two liquids of slightly different density cause a problem, especially with the pump! Thanks
leonard57, Jan 5, 9:40am
8-lol,nice one
michaelqian, Jan 5, 9:45am
Actually forget about that last post. If I have say 80% water and 20% coolant in my system, I imagine there will be a risk of the water boiling! If the engine reaches around 100C and the water boils, wouldn't I run a risk of something blowing up!
00quattro00, Jan 5, 9:50am
Water boiling temp is raised when under pressure
chris.f, Jan 5, 9:50am
Unless your running a non pressurised cooling system, the boiling point of the water will be above100deg C, the actual boiling point dependent on the PSI rating of the cap.
gunsmoke4, Jan 5, 9:56am
100 at sea level.
johnf_456, Jan 5, 10:05am
anti freeze is also anti boil as well
morrisman1, Jan 5, 10:06am
Just use tap water, unless your tap water comes from an underground bore, then Id be a bit more careful.
lugee, Jan 5, 10:10am
Most municipal supplies are bore water.
granada, Jan 5, 10:16am
I think the real question is when are you going to get it fixed. Tomorrow, next week , next month or next year. The answer to this question will determine what type of water you need.
When it is sorted drain and replace the coolant with the quality and mix as specified by BMW.
meathead_timaru, Jan 5, 11:17am
You're confusing density with viscosity.
budgel, Jan 5, 9:48pm
Get it fixed ASAP!BMWs seem to be more sensitive to cooling issues than most cars from what I see on BMW forums.
lazeeboy, Jan 5, 11:21pm
You have absolutely no clue.
thejazzpianoma, Jan 6, 1:30am
Yes there is, that is why the manufacturer usually says not to do it.
Sometimes you might be O.K, sometimes you may not, depends on whats in your local water supply. Why you would be lazy and use tap water in a modern cooling system escapes me given the low cost of demineralised water.
a.woodrow, Jan 6, 1:38am
Why! because they have a coolant leak and the motor is probably already wrecked. That's why.
kazbanz, Jan 6, 2:04am
OP-frankly I wouldn't be mucking around with your car.
Its a 2003 car worth what -10-20k
So if the car is at home -LEAVE IT THERE.
Organise for the radiator top tank (or complete radiator) to be replaced/repaired.
Put tap water in TO DRIVE IT TO THE RADIATOR PLACE. Tell the radiator place what you have done so they can flushthe system and put the correct coolant into the car.
Otherwise you may well find you are up for a VERY expensive repair later
mugenb20b, Jan 6, 2:09am
"demineralised" water.but how do you know it's not just tap water they are trying to sell you!
purple666, Jan 6, 2:10am
Well I for one never thought I would see the day when tap water wasn't good enough for your radiator, and they call this progress!