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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
    
I like your contributions. Just started driving last month, I will start contributing after gaining more experience in driving. Thanks. – user6906 Sep 5 '14 at 13:03
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From your update, it sounds like you may have blown your headgasket. You'll need to have a compression test done to verify. – Juann Strauss Sep 5 '14 at 13:14
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@JuannStrauss - It is interesting that you mention that. About a year after this happened the car did blow its head gasket. It caused the engine to be flooded and as a result we had to replace it. Perhaps these were just the first signs of the gasket going. – Travis J Sep 5 '14 at 20:26
up vote 7 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

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

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

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

I am glad you got a good outcome, but would like to answer because I have a fair amount of experience with difficult cooling system issues, and the most recent one occurred while I was over 1,000 miles from home. Had I been close to my home it would have not been very inconveniencing. On top of that, it was the hottest time of the year and I had traveled 1,000 miles south into hotter territory. The issues began about 40 miles from home and I made the very bad decision to top off the coolant and proceed rather than turn around back home and choose a different car. Below is my advice based on a lot of experience with managing a vehicle that is overheating.

First rule is simple -- if the temperature is above the normal (usually half-way, or in some cars just a hair above half-way on the gauge), pull over and stop the engine. That is your safest bet to avoid damage and turning a minor problem into a major one. Most cooling issues are solved by replacing a hose, an $8 thermostat, a $50 radiator fan motor, or a $200 radiator. Water pumps are cheap, but not easy to change on a lot of modern cars, so I don't consider that a "minor" fix because of the high labor costs. Driving the car after it crosses the normal temperature for any amount of time increases the chances that a cheap problem will turn into a $1,00 head gasket or $2,000 engine rebuild.

If for some reason you cannot do that, your first order of business is to turn off the air conditioner, roll down the windows, and turn the heat onto the hottest and the blower to full blast. This will increase the cooling system capacity by allowing the heater core to dissipate engine heat -- obviously at the expense of cabin comfort. Also, by killing the AC, the AC condenser is no longer dumping an additional heat load onto the cooling system. If you do this and the temperature stays within normal range (which is often the case) pull over when you can and check the coolant level.

If the coolant level is down, fill it. If you cannot get proper coolant and have to use water from a jug or a hose, that is better than low coolant. Keep in mind that you should circle back after the repair and drain/flush and refill the system (if it was not required for the fix) so that you have the proper proportion of anti-freeze to water. Also keep in mind that spring water is best for your cooling system, and if you ended up getting it from a hose that might introduce contaminants that over time will cause problems, like corrosion or mineral buildup that clogs the radiator, etc. But, dirty water is better than no water.

If the coolant level was low, the question becomes "how fast is the leak"? If you can't see it, like gushing out of a broken hose or oozing from the radiator, then all you can really do is fill it and then proceed (AC off, heat on, driving very delicately) and see how far you get before the temp breaks the normal reading. Obviously, you carry extra water/coolant with you when you go down this path.

If the coolant level wasn't low, then proceed.

As you drive with a cooling issue you want to avoid stopped traffic and keep the car moving 20mph or better. The reason is the movement creates airflow over your radiator. When you are stopped in traffic, there is no airflow, and the only thing keeping you from overheating is the radiator fan -- and it is very possible that has failed and is the reason you overheated to begin with. If temps stay normal while moving but creeps up over normal while stopped, it is probably the fan. Avoid stopped traffic.

You also want to avoid heavy loads. You may be able to drive with a compromised cooling system at 55mph without overheating, but at 65mph it overheats. This is because engine load is higher, and if you are on the highway driving a long time with a compromised cooling system, the load is higher than the cooling system can dissipate the heat.

Hills are not your friend when driving with a compromised cooling system. If you can't get up the hill without loading the engine to the point it overheats, there isn't much you can do about that.

It is worthwhile to also check the auto transmission fluid, because if that is low the tranny is running hotter than normal and most radiators have a section that is your transmission fluid cooler which is mounted to the radiator putting additional heat on the cooling system.

Using these techniques you might be able to get a car where you need it to be with a compromised cooling system. It is impossible to guarantee results.

If the question becomes "how hot can I run it without doing major damage", the answer to that question depends on the specific engine. Some cars, such as those with steel block and aluminum head, any overheating runs the risk of warping the head (because steel and aluminum expand at different rates). If you can manage to get home or to a shop by using the above techniques, there really isn't too much to worry about. But if you can't do that and must press on with the temp over normal, you are running a serious risk of making a bigger problem. Whether damage is done depends on how hot it got and for how long.

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