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What happens if I drive without antifreeze in my car (no water / no antifreeze)? This is my main question. I've added some follow up questions that are specific to my situation but for the main question I just want to know in general what happens.

HISTORY
Let's say someone thought that the low antifreeze light was the low windshield washer light and drove a 12 mile trip to work and home from work in the middle of winter for a month? What happens if they drive in the summer?

UPDATE
For the record, for me, I realize now that I was driving with low antifreeze except for maybe one or two trips (of about 40). I believe a few trips I ran completely out because the temperature shot up 10 to 20 degrees over the span of a mile. I pulled over as soon as I noticed this and could pull off the road or into a gas station and added coolant.

I was able to take it in to get fixed. The mechanics ran pressure tests on it and found the coolant leak in the water pump. They replaced it and it's running fine since then. However, the engine seems to knock / rock very loudly sometimes at start but eventually dies down but that may have already been happening. I don't know. Anyway, no leaks.

NOTE
I took it to one shop and I said that I had a radiator leak. They ran pressure tests and said the radiator and water pump were leaking. I took it to a second shop and they said that only the water pump was leaking. Is the first shop's pressure tester unreliable?

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To clarify, were you low on coolant or at zero coolant? Those are two totally different situations. The first is potentially a don't care in the middle of winter, the second is potentially fatal for the vehicle. –  Bob Cross Mar 18 '13 at 18:55
    
Since this is theoretical (cough cough) what would happen if it was empty? –  1.21 gigawatts Mar 18 '13 at 19:05
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Oh! I've been checking the overflow tank! :P I remember that being empty once. I'll have to check the radiator the next time the light goes on. To answer your question when I would fill it up it was never more than one $10 container from the gas station. –  1.21 gigawatts Mar 18 '13 at 20:36
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Did the heater still work in the car when it was low on coolant? –  Larry Mar 18 '13 at 22:37
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In order for the heater to work you had to have a fair amount of coolant in the system. That doesn't mean it wasn't low, just that it wasn't empty. –  Larry Mar 19 '13 at 15:38
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4 Answers

up vote 5 down vote accepted

Without water and without antifreeze or just without antifreeze? I'll assume that you mean without either, but you should clarify the difference in the future.

This is really simple though. The engine will overheat, quickly, and the seals and gaskets will give out, letting fluids leak in and out of places they should or shouldn't be. Eventually, parts of the engine will stop working all together and depending on how long you let this go on for, the engine will need to be taken apart and repaired or it may just need to be melted down for scrap metal.

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I think you're fine but you need to get your leak fixed.

Based on the comments on the original question:

Oh! I've been checking the overflow tank! :P I remember that being empty once. I'll have to check the radiator the next time the light goes on. To answer your question when I would fill it up it was never more than one $10 container from the gas station.

This sounds like a slow leak of coolant from the system but not one that is terminal. There are two situations where this would really worry me (and did when I was driving a Mustang with a slow radiator leak):

  1. If I didn't bother to mix the coolant properly and had a period of serious cold weather without a lot of driving, giving the coolant a chance to freeze in the system. In fairness, I was young, dumb, poor, engaged and in graduate school. None of those are conducive to proper maintenance.

  2. If the weather got really warm and I was driving around at slow speeds, not letting the radiator get a chance to do its job. That situation is a prime candidate for overheating which will progress to the point of destruction (as described by @hillsons).

For clarity, I strongly recommend that you don't look for a coolant leak using your bare hand around a hot engine. That's an excellent way to get a terrible steam burn.

Instead, try wrapping a white paper towel around a wooden dowel. If the paper towel starts getting wet / turning green, you found the vicinity of the leak. If the dowel gets cut in half, the leak is really bad....

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Assuming you mean with just water and no antifreeze, as long as the outside temperature does not drop below 0°C, nothing bad should happen. If the cooling system is otherwise in good shape, plain water should be sufficient to keep the engine cool. If the radiator is partially clogged, or the thermostat isn't opening all the way or is not opening until the temperature gets much higher, or if the water pump is not working at full strength, then having plain water (which boils at a lower temperature) may lead to overheating. You might also have an overheating problem in extremely hot climates. In any case, the engine temperature gauge on the dash should show you whether you have overheating; if the temperature is below the mid line, it's safe to keep driving.

If on the other hand you mean with no fluid at all, it's almost certainly impossible to drive the vehicle without major overheating and engine damage. If you have a really small 4 cylinder engine and the outdoor temperature is well below freezing, however, you might be able to get by with just air cooling as long as you keep moving fast. I wouldn't try it unless you're prepared to rebuild or replace the engine, though. :-)

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Water will boil at a lower temperature, however, water is a better conductor of heat than antifreeze, so your assumption that water wouldn't work as well in hot climates seems incomplete. In climates where freezing is never an issue, water would be a better fit for the job, were it not for a little problem called rust, antifreeze is still necessary for rust prevention. –  hillsons Mar 15 '13 at 20:50
    
Always remember that heat accelerates chemical reactions. An engine cooled with tap water will accumulate the equivalent of years' worth of rust in just a few days; also, besides eating away at the inside of the engine and radiator, the rust tends to "silt up" and block the coolant lines. –  MT_Head Mar 15 '13 at 21:33
    
Thanks. It's just empty. No water, no antifreeze. I'm waiting for my paycheck to come in as I keep refilling it (and then a day later the light comes on). –  1.21 gigawatts Mar 18 '13 at 15:02
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A dry radiator will cause overheating that is likely to warp cylinder heads and do even more damage. This is expensive to fix.

An empty overflow tank should be topped up with a 50/50 mix occasionally until you get to a repair shop. Keep an eye on your temp gauge and stop driving if the needle is in the red! Your coolant leak prevents proper pressurization and leads to higher coolant temperatures (lower boiling point) and harmful air pockets that cause localized overheating and cavitation that will damage your water pump over time.

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