Can I put water into my car radiator?

How to keep your car radiator cool in an emergency

We’re often asked, “Can I use water instead of coolant for my radiator?”

You can put water into your car radiator if your engine is overheating or the coolant overflow reservoir is very low or empty − but only if you have no other option.

You should only consider this when you intend to drive a short distance. You’ll want to ensure that you flush and refill the radiator with the correct coolant mixture when you arrive.

Natrad can provide you with exceptional engine coolant products and advice. Nip into Natrad to get the right coolant for your vehicle.

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How To Check For A Problem With Your Car’s Cooling System

The first sign of a problem with your car engine and cooling system will appear on your dashboard, where a thermometer symbol will light up. This symbol indicates that your engine is overheating. However, there’s no way to tell just yet why it’s overheating — a component could be broken, or you may have a coolant leak.

What Do You Do If Your Car’s Radiator Stops Working While You’re Driving?

If your engine temperature is rising, you should pull over immediately before your vehicle’s engine overheats.

Never open the coolant pressure cap when the engine is hot, as steam or hot coolant could cause injury. Allow the car’s engine block to cool, and check the coolant overflow reservoir level. If it’s really low or empty, you’ll need to decide whether to:

1. Call your roadside assistance provider for help, or
2. If you know where your nearest Natrad store is, you may be able to drive to us yourself

If you choose to drive to us, you will need to top up your car’s radiator fluid.

If you do not have proper radiator coolant with you, then you can top up your radiator with water in an emergency — but only in an emergency.

Water is not a good substitute for coolant because of its long-term effects on your vehicle’s health. But it is better than nothing.

How long can I drive my car without a working radiator?

Without its radiator, your car will run for roughly 5-15 minutes before the engine overheats. How hard you push the engine, your vehicle’s speed, the strength of the wind, and the temperature outside will also affect how long you can drive.

If you’re going to drive, do not allow your engine to overheat. Driving with an overheated engine can cause significant damage.

How To Fill Your Car Radiator With Water

Here are the steps to take to safely top up your radiator’s coolant levels with water.

1. Make sure that your engine is off and cool, and the vehicle is in Park with the parking brake on.
2. Let the engine cool down before you remove the coolant reservoir or radiator cap. If you attempt to remove the cap while it is still hot, hot coolant can sputter and cause burns.
3. Loosen the cap carefully, using a towel or thick cloth to protect against possible scalding from pressurised gas or fluid. Step back and allow the pressure to release before removing the cap completely.
4. The coolant reservoir will have a ‘Full’ line indicator. Add water until it reaches that line. When adding water directly to the radiator, fill it to the brim.
5. Replace the cap, tighten it until it clicks and shut the bonnet of the car.

How much water does a car radiator hold?

If you’ve had a leak and your radiator is entirely empty, you’ll need to fill it as full as possible before driving it to a mechanic.

To see how much coolant your radiator holds, consult your owner’s manual. It will give you an exact figure. That’s how much water you will need. You can also simply fill your radiator until the liquid inside reaches the “Full” line. 

What Type Of Water Is Best?

If you don’t have coolant available, you should top up your radiator with the highest quality water that you have. Ideally, this would be distilled water. You can also use bottled water or tap water.

Bear in mind that tap water or bore water contains minerals that can leave deposits throughout your cooling system, contributing to corrosion which will reduce the lifespan of the radiator and other components in the cooling system.

Once you reach your closest Natrad store, you must tell our mechanics that you’ve put water in your radiator and what kind of water you’ve used. We’ll flush it all out, clean your radiator, and then top it back up with proper coolant.

Pros and Cons of Using Water

To understand what plain water does to your radiator, you need to understand what radiator fluid actually is.

Radiator fluid (also called coolant or antifreeze) is a 50/50 mixture of distilled water and either ethylene glycol or propylene glycol (plus various corrosion inhibitors and other additives, depending on the brand).

These coolant ingredients have several important functions: 

• Preventing corrosion
• Increasing the boiling point of the water
• Lowering the freezing point of water

These qualities are what makes coolant so effective. But when you add water to the radiator, you dilute any coolant remaining in the system, reducing its corrosive inhibiting and temperature-resistant properties.

You can drive your car if its radiator is mostly or entirely full of water, but only for a short duration. The longer your engine operates with just water, the more lasting damage can occur.

When Can I Add Coolant To The Radiator Again?

Have your radiator checked over by a technician to determine why the coolant was low in the first place. The technician will locate and repair any leaks, replace any compromised parts of the cooling system (like the water pump) and flush the system before replacing the coolant.

Flushing the radiator is essential before coolant is topped up again. Neglecting to flush your radiator properly can lead to its failure. Make sure that your technician does a complete radiator flush after the cooling system has been repaired.

Once the radiator has been thoroughly flushed, you should fill it with the appropriate coolant solution, as specified by your vehicle manufacturer.

If you get into a situation where you must drive your car using water as the coolant, make sure that you get the vehicle to a radiator technician and determine the cause of the coolant loss.

Repairing the radiator as soon as possible will reduce the likelihood of potential extensive damage to the radiator, heater and engine.

A Natrad technician can diagnose a radiator problem, repair and flush your radiator. We stock a variety of high-quality coolants and will refill your vehicle with the correct coolant to ensure your vehicle runs smoothly.

Ask at Natrad for radiator repairs, top-up coolant or a cooling system flush.