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Currently own a Vauxall Corsa (diesel), that is seemingly leaking engine coolant. Having bought over 3 bottles of coolant this week, and having to fill it up constantly, I will be taking it into a mechanic this weekend to see what's wrong. Because of this leak, the engine temperature warning light constantly lights up as the coolant runs out.

To save the expense of further bottles of coolant (and seeming that it's just leaking out anyway), and just as a temporary measure, can I simply use water instead? We are in the UK, so the temperature here currently is of no concern for anti-freeze.

Would this cause any damage in the short term? Depending on the fix, I might not be able to afford the repair straight away, would water cause an issue for a few weeks of driving? (Not major mileage, maybe 15 miles a day).

marked as duplicate by Pᴀᴜʟsᴛᴇʀ2 engine May 31 '18 at 22:13

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    Short term is ok, but water will boil at a much lower temp than anti freeze, so it could overheat if pure water in the cooling system. – Moab May 31 '18 at 20:10
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    There are other long-term issues with this strategy, but I agree with Moab that as a short term strategy it shouldn't cause you any heartburn. Plus you wont be leaving puddles of coolant all over town. – Tim Nevins May 31 '18 at 20:36
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    How old is the car? The most common cause of coolant leaks is just a broken (rubber) hose. If that is the cause, your mechanic should be able to fix the problem this weekend relatively quickly/cheaply. If you are able to locate a tear in one of the four (?) hoses which carry coolant, you might be able to fix it yourself. There are usually 2 thick hoses going between the engine and the radiator. Another 2 thin hoses go from your engine to the firewall (these thin hoses warm the cabin when you turn on the heat in your car). – Sam May 31 '18 at 22:08
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You can run with water in the system and the pressure cap will raise the pressure and therefore the boiling point of the water so that will be fine.

The issue you will face is that the “anti-freeze” is not only to prevent freezing, but it has corrosion inhibitors in it to protect the various metals used for the engine block, water pump and vanes and radiator.

You should get this leak fixed as soon as possible and get the correct coolant fluid in it, mixed in the correct proportions.

Edit re the temperature change caused by antifreeze : yes the antifreeze will cause the water mix to boil at a higher temperature - about 10 degrees F or some 5 deg C - the temperature difference caused by the pressure difference will cause the boiling point to go up to about 120 deg C ie 248 deg F...

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    How long could you run with just water realistically before causing damage? – PnP May 31 '18 at 21:07
  • Electrolysis won’t wait for you so as I said get it done... – Solar Mike May 31 '18 at 21:10
  • Understood, but for a few days before I can physically get it to a mechanic, wouldn’t be dangerous? – PnP May 31 '18 at 21:11
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    Regarding the pressure cap increasing the boiling point, this is only true in closed systems. If the engine has a leak, pressure will be released, and the system will never fully pressurize. Note: This will not hurt the engine from a mechanical standpoint, but the water will start boiling. – Sam May 31 '18 at 21:46
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    @Sam not air but water vapour ie steam which is water in a different state but not the same as air, it has different properties saturated or not, dryness fraction etc – Solar Mike Jun 1 '18 at 4:39
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This is such a complex topic. I suggest you read this entire article about the topic. I learned SO much from it, and I'm sure you will as well.

From my experience, you will be OK using distilled water. (Make sure it is distilled, absolutely not water from the tap!)

Most race tracks only permit cars and motorcycles to use only water, in case there are spills on the track (antifreeze is very slippery). So I'm sure using straight water will be fine in a daily driver. Just keep an eye on how much water you have in the system. The worst thing you could do is let the water level get too low with the engine running.

To try to prevent corrosion, you could add 1 part antifreeze and 10 parts water whenever you top the system off. I don't know how the antifreeze prevents corrosion in the engine (snake oil??), but since most manufacturers suggest a 50/50 water/AF mixture, keeping a small amount of AF in the system will certainly help.

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    Over prolonged use, water (even distilled) will almost certainly lead to corrosion. As temporary fix, no problem. Race tracks mandate pure water for the reason you described (slippery if leaked), but also pure water provides better cooling than antifreeze - obviously important when pushing an engine really hard, and more important than corrosion protection. – masospaghetti Jun 1 '18 at 17:36
  • Definitely. According to the graph of the specific heat capacity of a water/AF mix in the article I linked, 100% water has a ~15% higher specific heat capacity than a 50/50 mix. Certainly fine as a temporary fix in the case of the OP, but as you say, long term it's not a good idea. – Sam Jun 1 '18 at 18:20

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