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Today, after a very hot day, I saw that my coolant was almost reaching 100C/212, I pulled over, stopped and took a look over the hood. The very little water that remained in the coolant tank was all boiling. So, I went to a gas station, bought some water and refilled the tank. When I got home, almost the same problem, the water in the tank was boiling.

Now, my questions:

  1. I would like to drive the car to the nearest qualified service, but there is a fair distance to it (about 8km) as I'm living in a remote location. Is it safe to drive it that distance if I refill the entire coolant tank?

  2. What can the cause be? I know that is impossible to diagnose a car without seeing it, however, if you have any idea what could the problem be, I would really like to hear it.

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@mindnose, I think this is a great question. I assume that you're talking about the overflow tank when you said you checked the "coolant tank". If you'd opened the radiator cap, I think you would have had terrible burns. –  Bob Cross Jul 11 '11 at 1:33
    
Yes Bob, indeed, I didn't touch the radiator cap. Even the overflow tank was very very hot because the water was boiling in it, so I had to use some tick cloth material to open it. –  Valentin Radu Jul 11 '11 at 10:40
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6 Answers 6

up vote 11 down vote accepted

I would like to drive the car to the nearest qualified service, but there is a fair distance to it (about 8km) as I'm living in a remote location. Is it safe to drive it that distance if I refill the entire coolant tank?

I would say yes, you can drive the car. Load the car with much more water than you think necessary: I find that two liter soda bottles make excellent transport and pouring vessels for this sort of thing. While driving, watch your gauge: if you see a high reading, get out and add water to the overflow tank (never open a hot radiator cap). Repeat as necessary.

What can the cause be? I know that is impossible to diagnose a car without seeing it, however, if you have any idea what could the problem be, I would really like to hear it.

The water is clearly doing what it is supposed to do: carry heat away from the engine. Unfortunately, something is preventing the heat from leaving the water (e.g., sludge as previously mentioned, fouling in the cooling fins or just impeded airflow) or you have a leak.

I think that your instinct to go straight to a service station is a great idea.

If, however, you were to choose to try to diagnose this situation yourself (which I'm not recommending if you're not feeling confident), you could try running the car up to temperature, turning it off and listening and looking for a pressure leak (hissing and / or white steam).

For clarity, never never never feel around for a steam leak with your bare hands. Best case: you'll get a terrible burn.

Following up on that last paragraph to add this lovely quote from Dan:

Clouds, and the visible "steam" squirting out of a kettle or a steam locomotive, are liquid water droplets with a ceiling temperature of 100°C at sea-level air pressure. It's possible for actual invisible-vapour steam to be swirled in with condensed droplets as it mixes more or less chaotically with the outside air, but "pure" steam is invisible, and has no ceiling temperature. Put your hand in the visible portion of the steam coming out of the side of a locomotive and you may get scalded, but putting your hand in the invisible jet close to where it's exiting may flense the flesh from your bones.

The key phrase there is "no ceiling temperature."

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Thanks Bob for this very good answer. Indeed I think it has a pressure leak as you said, because this morning I started the engine, fulled the tank, and after a while I heard the hiss (however saw no steam). More than that, it seems the water gets 'consumed' quite fast. Will go straight to a service station. Thanks for the answer! –  Valentin Radu Jul 11 '11 at 11:01
    
@mindnoise, good luck, those radiator leaks are super annoying. –  Bob Cross Jul 11 '11 at 18:28
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Your coolant shouldn't be boiling at 100C/212F if you have a proper mixture of water and anti-freeze (typically 50/50 ratio is recommended).

Water's boiling point is 100C/212F. Even though it is called anti-freeze, it also raises the boiling of the water.

You can buy a coolant mixture tester for a few dollars at a local auto parts store, you suck some of the fluid up into it and it will show what the freezing and boiling points should be (mine is about 270F).

Still attack the other items listed in the other answers, but it sounds like you are running none or almost no anti-freeze in your system and so getting some in there will allow your cooling system to continue operating at the higher temperature until you get the source of the problem sorted out.

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You are correct: "With proper antifreeze a wide temperature range can be tolerated by the engine coolant, such as −34 °F (−37 °C) to +265 °F (129 °C) for 50% (by volume) propylene glycol diluted with water and a 15 psi pressurized coolant system" from en.wikipedia.org/wiki/… –  Bob Cross Jul 11 '11 at 18:26
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When I've had overheating problems and unable to get it fixed or checked out immediately, driving with the heat on full blast (yes, in the summer) is an excellent way to reduce the engine temperature and get you to where you need to go without damaging your engine.

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Yes, I had to do exactly this when I had my radiator hose blew. Driving around in big clouds of steam while roasting alive inside the car is not super duper fun. –  Bob Cross May 10 '13 at 19:46
    
open windows, point the vents out the car. –  Juann Strauss Apr 9 at 11:05
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You shouldn't be losing fluid - did it all boil off?

If you are ending up with low coolant, I would suspect a leak.

If the level is okay, I would suspect either a restriction in a pipe or the radiator itself, or possibly a damaged thermostat restricting the flow.

Check for a bent or twisted radiator hose or damage to the radiator.

If nothing is obvious, I would make sure the coolant level is where it should be then drive slowly to your garage - you did say this only happens at higher speeds.

The radiator could have a build up of rust or sludge, so having a garage flush it could be useful, and they can get a full check of the colant circulation path.

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Hey be carefull but not overly worried.

Probably everything was fine, the cap on de radiator keeps the water under pressure so it only boils above 120 C. I was not boiling, only when you opened the cap and the pressure was gone. Very dangerous to open that cap on a hot engine.

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the bottom radiator hose contains a spring to prevent collapse.These sometimes corrode so if your hoses are old could be worth a look

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