Can I put water in the radiator in an emergency?
You’re on a family trip and just a few hours from your destination when your car’s temperature gauge starts to spike and an unexpected event abruptly ends your trip.
A quick look under the hood reveals that the cooling system’s overflow tank is low on coolant and has an obvious leak. The salesperson offers you a few gallons of water to top off your car’s cooling system, even though the closest store within walking distance doesn’t stock any coolant.
This raises an interesting question: Can I add water to my car’s radiator or cooling system in an emergency? Does this pose any danger to my car’s engine?
What if I use water instead of coolant? In most cases, it is completely safe to top up your vehicle’s cooling system with water in an emergency. However, before you do this, it is important to understand that water offers no protection from antifreeze, and furthermore, it boils at a lower temperature than antifreeze.
Therefore, water should only be used as a temporary substitute for coolant. Your vehicle’s cooling system should be refilled with the proper coolant once the underlying leak has been repaired. If this water is not replaced with the proper coolant, a variety of problems can occur over time.
Long-term use of water can cause corrosion in your vehicle’s cooling system. If this corrosion is allowed to worsen, rust particles can clog the cooling tubes and clog the radiator, making overheating issues even worse.
This corrosion cycle is difficult to stop once it begins and can cause overheating issues for years to come. Water has no freeze protection, so you should drain it from your engine before the cold sets in. When water freezes, it expands and takes up a much larger volume than it does as a liquid.
Most engines have freeze plugs designed to relieve the pressure from this expansion, but there is still a high risk of damage if water in your engine’s cooling system freezes.
Engine blocks and cylinder heads have been known to crack and break due to the stress caused by the expansion of frozen water. With that much expansion, even your cooler stands little chance. In the end, such issues often turn out to be much bigger problems than the problem that caused the engine to originally leak coolant.
Does the type of water matter?
While any type of water should never be used (alone) for extended periods in an engine’s cooling system, some types of water are more suitable for such purposes than others. This is because certain types of water increase the risk of corrosion and limescale build-up in the cooling system.
If possible, you should avoid using ordinary tap water for such purposes. Tap water contains many minerals that act as corrosion catalysts. Therefore, using tap water in your engine’s cooling system can promote the formation of problematic deposits and, in turn, cause overheating problems.
To avoid problems caused by tap water, soft or purified water should be used as an alternative whenever possible. However, distilled or bottled water can also be used for the same purpose if it is readily available.
Uses: Purified, soft, distilled water
Do not use: Tap water, spring water
Will my car overheat if there is only water in the radiator? Water is relatively efficient at cooling an engine, but it has a slightly lower boiling point than coolant. Water boils at a temperature of 212°F, while 50/50 coolant boils at 223°F.
This difference may seem small, but it is significant enough that coolant is much more effective than water at preventing boilover. Therefore, using only water in a vehicle’s cooling system will make the engine more susceptible to overheating under intense or harsh conditions.
While this inefficiency may not be obvious at cruising speeds, drivers should be aware of the fact that their engine will not be adequately protected from overheating if they are using pure water in their cooling system. Should I pour water on my engine to cool it down?
When an engine overheats, most drivers obsess over using any means possible to provide additional cooling. However, acting immediately without considering the possible consequences can cause more harm than good. A classic example is pouring cold water on an overheated engine.
The reason is very simple: When metals, such as engine blocks and cylinder heads, heat up, they expand. When they cool, the metal contracts again, returning to normal.
If the heating/cooling is done slowly, the metal can withstand these fluctuations. Rapid heating or cooling, on the other hand, can cause one or more cracks in the metal surface.
Dousing an overheated engine with cold water is a major cause of thermal shock damage. When an engine is cooled rapidly by pouring water on it, the block and cylinder head shrink rapidly.
In most cases, this results in the formation of one or more cracks in the engine’s vital structural components. Repairing this type of damage can be quite costly, sometimes exceeding the total price of the vehicle itself.
How to Safely Refill Coolant in a Radiator Water can be used to refill a vehicle’s cooling system in an emergency, but there are some special steps you should take if you intend to perform such a task.
By following the steps below, you can safely fill your engine’s radiator with water.
#1 – Let the engine cool
You should never add water to a warm engine. Conversely, you should wait until the engine cools down to ambient temperature before refueling the system.
#2 – Remove Cap
With the engine cooled, you will now remove the fill cap to your engine’s cooling system. In some applications, this cap will be found along the upper radiator tank, while other systems will be capped at a remote overflow reservoir.
In any event, this cap should be opened slowly, with the use of a rag or towel covered hand. You DO NOT want scalding hot coolant spraying on your hands, arms, or even face.
#3 – Add Water
Water should be added slowly to any cooling system, allowing as much air to escape from the system itself as possible. Most overflow reservoirs are stamped with a “full” mark, which will provide visual confirmation as to the level of fluid within the system.
Alternatively, systems without a radiator should be filled until reaching a level just beneath the radiator’s fill neck.
#4 – Burp System
With water added, it will now be time to “burp” your engine’s cooling system of air. This is accomplished by letting the engine idle, with the system’s fill cap still removed. You should notice small bubbles being expelled upward through the water contained within the system.
Burping should continue until the engine has heated sufficiently enough, to allow the system’s thermostat to open. At this point, water again will be added as necessary, and the system’s fill cap will be reinstalled.
#5 – Keep A Watchful Eye
When driving, one should keep an eye on their vehicle’s temperature gauge, in a bid to identify the earliest signs of overheating. Identifying the root cause of your engine’s initial coolant loss should also take precedence.
Once all repairs are made, water should be drained from the system, and the appropriate coolant added. Be sure to consult your vehicle’s owner’s manual, when determining the types of coolant that are acceptable for use.
