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)?
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.