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Recently, I was informed that a car I share ('02 Nissan Sentra) was close to overheating. I was told it gets close to the upper limit very quickly upon running the car. When I inspected the vehicle, I realized that the coolant overflow was empty and the radiator's coolant level was rather low (not sure exactly how low but it seems at most 75% remains).

The car must be taken to a mechanic. However, the mechanic I trust and usually use is about 30 miles away. I assume there is a leak in a hose, connector, or perhaps the water pump. The radiator is new so I do not suspect it is the source of this issue.

Because I am assuming there will be a leak, I think that when I drive it, it will most likely loose coolant. Also because of this assumption, I am weary of putting coolant in if it is just going to leak out.

I am assuming I will have to make a few stops to fill the overflow (not touching the radiator). Can I put pure water in the radiator and overflow tank and limp the car 30 miles (mostly on the freeway - yikes)?


Edit

Great answers here, I just wanted to post what I actually ended up doing in the hopes of it helping someone at some point, or maybe to satisfy curiosity.

I decided not to go with pure water because I have read that a 50/50 ratio of coolant to water is desirable and figured even if it were leaking, should it be slow, I should follow best practice.

I was unsure what type of coolant my car used, so I just went to the dealer and got a container of what was standard.

The reservoir was completely empty, and the radiator had a low level of water. I added some water (maybe 1.5L) to the radiator to top it off and I filled the reservoir to the "MAX" line.

I read from a post that a simple test you can do is to start the car, run it a little, turn it off, and then listen for a leak. I tried that, but perhaps the car did not get hot enough, or there wasn't a leak evident to that method.

I then looked on the ground for any evidence of a leak and saw none. I started the car and let it run while looking to see if any fluid was leaking and could not see any after a minute or so.

After this I drove the car trying to maintain under 3000 rpm and made it to the mechanic's shop like that.

Overall, I would say this situation was mild in comparison to what could happen. I am definitely not recommending to drive a car with a major leak, or even with a medium one. My car exhibited no signs of leaking and based off of that I drove it.

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I fill up water in my radiator like every 3 days just to be sure that it would not overheat..I drive a nissan sentra b13 and our place is tropical so I dont think that coolant mix would be necessary since our climate would not freeze the engine. Im not sure if my radiator or hoses have a leak somewhere..but if i forget to put water like after 4 days my car would overheat..any ideas on this?? –  user3588 Aug 21 '13 at 15:51
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5 Answers

up vote 6 down vote accepted

First thing I'd try to figure out is how quickly it leaks - run it, stick your head underneath it as check if there is any visible leaking. If there is, chances are that it's not going to make it for 30 miles. I'd also check for any evidence of oil and water mixing. If there is, don't drive it.

If it's not leaking that badly I'd be tempted to top it up with plain water just to check if that reduces the temperature to something more normal. If it doesn't there's a chance that you either have a thermostat that's failed closed, a blockage in the cooling system or a really bad water pump. Again, check for leaks with the engine running and warm, any visible leaks this side of the odd drip and I'd be very careful about driving the car.

In general, water on its own tends to cool better than water + antifreeze, so you're not risking any damage from running water in the engine provided the outside temperature doesn't drop below freezing. Even then, you probably are going to be OK as hopefully there is a little antifreeze left in the existing coolant. Either way, advise the mechanic that he might have to drain the cooling system immediately depending on the outside temperatures.

If in doubt, I would get the car transported to the mechanic - even if you pay retail for the recovery it's likely to be cheaper than a blown engine, unless the engine is fairly terminal already.

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The first thing you would try is in essence what I did. See my edit for more details. –  Travis J Oct 25 '12 at 17:15
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I agree with Timo - if it is a big enough leak that you can see it clearly, then getting the car transported is much safer.

In general, using water as coolant is OK for a short time or as a "get you home" alternative, but it does not have the anti-freeze and corrosion inhibiting properties of a proper coolant mix, so should not be left in the engine for any length of time, especially if you live in a cold climate.

Additionally, you should avoid adding cold water to a hot engine unless you have no other choice - there is a risk that it can cause a thermal shock and risk cracking the block, which would end up very expensive!

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Good point about the cold water in a hot engine. Although I did not end up doing this, I had considered buying a gallon of water from a gas station and might not have even thought about this common scenario which can be easy to overlook. –  Travis J Oct 25 '12 at 17:15
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If you think there is a leak and have 30 miles drive, then you can reserve some pure water with ride and use it. pure water is not alternative for radiator coolant, because water will be boil quicker than coolant. but its far better than running empty coolant.

One more thing if you are living in cold area do not keep water inside radiator long ,It will freez and make more problems

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I went to the dealership and got some coolant from them to use figuring it would most likely help at least a little to have some in there. Do you think I should stick with water or use a mixture? Silly question: the overflow reservoir should not be empty, right? –  Travis J Oct 25 '12 at 6:09
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I don't think mixture will be problem for a 30 mile drive . yes reservoir should not be empty. –  Ullas Prabhakar Oct 25 '12 at 6:34
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If there is a major leak 30 miles may be too far, and you may cause major (very expensive) damage to your cylinder head or engine block.

Please read this question on driving without coolant! for some good advice (which broadly speaking boils down to don't do it!)

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Kind of banking on a small leak. If it is out of hand then AAA will pick up the slack. Mostly I was concerned with whether or not to just use water in the system while testing to see how bad the leak/situation was. –  Travis J Oct 25 '12 at 8:28
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If the leak is small you can definitely use water - distilled is better than tap water, obviously, but for a short run impurities won't do much damage. –  Rory Alsop Oct 25 '12 at 9:04
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If you are living in tropical climate, coolant is not needed as long as your radiator and water pump is in good condition. Make sure water is always full in your radiator and half in your reserve tank. Anti-corrosion is recommended as a protection to the internal of the cooling system against rust. David

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You are saying "coolant" when you actually mean "anti-freeze" ... and I would completely disagree with you. Anti-freeze is also an "anti-boil" as well. It moves the boiling point of your coolant up to ~240F I believe, then pressure on the system moves it up even more. It also provides the corrosion resistance you suggest. –  Paulster2 Mar 4 at 19:56
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