Rust in Coolant: Causes and How To Fix the Problem Easily

Rust in coolant may appear insignificant, but it can cause damage to your vehicle if left unchecked. A rusty coolant can be caused by several factors, one of which is insufficient coolant level. If you leave your coolant rusty, it can leak or even become jammed.

Rust in Coolant Causes and Fixes


This complete guide will discuss the possible causes of a rusty coolant and how you can immediately fix this.

What Are the Reasons for Rust in Coolant?

The reasons for rust in coolant can include insufficient coolant levels, using a worn coolant, water pump leak, or air trapped in your radiator. However, some other factors can also cause rust to appear in your coolant system, and these include:


– Water Pump Leak

A common cause of rust in your coolant system is a water pump leak. A water pump is an essential component of your vehicle that helps circulate coolant from the radiator to the engine and back.

Although it doesn’t seem like much, a water pump plays an important role because it prevents your engine from overheating. The water pump comprises several gaskets that can get damaged due to long-term use. When this happens, your coolant will leak and cause rust in the coolant system.

A telltale sign that your water pump is leaking is that you’ll notice a puddle of coolant under your vehicle. You may also notice that your vehicle overheats and produces more smoke from the hood. Upon close inspection, you may also detect whining and weird noises coming from your vehicle, as well as corrosion on the water pump itself.

– Using the Wrong Coolant

Using the wrong type of coolant can also cause rust to form on your coolant system. Most car models have recommended coolants that car owners should use. Although it doesn’t seem like a big deal, using the wrong coolant can affect your coolant system and cause rust to form on it. Also, using the wrong type of coolant will affect your coolant system’s performance.

In the same vein, mixing several types of coolants for use isn’t ideal because it can lead to serious damage due to their different compositions. The wrong coolant won’t only cause rust to form on your coolant system but will also cause damage to your cylinder gasket, the radiator and its hoses, and even the water pump. Some symptoms of using the wrong coolant include engine overheating and underperforming, and reduced fuel economy.

– Insufficient Coolant Levels

Rust in your cooling system can also be caused by insufficient coolant levels. Since most cooling systems are made up of metal materials, having less coolant flow through will cause them to rust. Also, a radiator leak can cause low coolant levels through the engine head gasket. Whatever the cause, having insufficient coolant level will not only cause rust to form, but your car will also start to underperform.

You may notice that your engine overheats, and the temperature gauge will be very close to red. Your car AC will also start to malfunction. Another symptom of insufficient coolant level is that your car produces a weird, sweet odor.

– Air Trapped in Radiator

Another common cause of a rusty coolant system is air trapped in the radiator. The radiator helps to reduce engine overheating and acts as a pathway for the coolant to get to the engine block. When air is trapped in your radiator, it will prevent the coolant from circulating to components where it is needed. Several factors are responsible for air getting trapped in your radiator, and the most common one is a broken radiator cap.

You can also get air in when you have a blown head gasket, leaking radiator hoses, or even improper coolant levels in the car. Also, the air gets trapped in the radiator if the coolant that doesn’t get through cools when you turn off the engine. Ultimately, these cool coolants contract and then cause air pockets.


– Worn Coolant

Not changing your coolant after long-term use can cause rust to appear in your coolant system. Coolants are made with several additives that contribute to their effectiveness. However, like most products, coolants have an expiry date and need to be changed.

It is normal not to pay attention to this, but using a coolant past its expiry date can cause issues to your cooling system. It could lose its additives and become acidic, causing rust to form on the metal parts of your coolant system.

Replacing Car Worn Coolant

If your car starts to overheat easily while driving, it is a sign that it needs more coolant. Also, pay attention to your air conditioning system. If it starts to malfunction, it is another obvious sign that your car needs more coolant. You’ll also notice that your car makes weird gurgling noises as well. Once you detect all of this, top off the coolant immediately.

How Do You Fix the Problem of Rust in Your Coolant?

To fix the problem of rust in your coolant, you need to top up coolants where necessary, flush out excess coolants, and bleed out air from your radiator. Although this issue can be slightly worrying, it is usually easy enough to fix.

Remedies of Rust in Your Coolant


Here are some great fixes for rust in your coolant:

– Flush Coolant System

The most efficient way to eliminate rust from your coolant system is to flush it. You can start by draining the coolant system of residual coolants. Ensure it is drained properly, then rinse the cooling system to remove residual dirt, debris, or contaminants. Once that is done, refill the coolant system with fresh coolant and add a rust inhibitor.

Carry out proper cleaning using clean water to remove any remaining dirt or particles. Refill the cooling system with fresh coolant and let the engine run for some minutes. Doing this will bleed out excess air that may have gotten into the radiator. Shut down the engine after about 15-20 minutes, then replace the radiator caps and screw them tightly.

Adding a rust inhibitor will prevent the cooling system from getting rusty or corroded. After doing this, bleed out the radiator so that air pockets do not form, and that’s all.

– Add Coolant the Right Way

You can properly add coolant to a car by turning off the vehicle’s engine and waiting for it to cool. Pop open your hood and locate the radiator. Take out the radiator cap and add new coolant to the radiator cap once you’re certain the coolant level is depreciated. Make sure to add the coolant carefully and avoid spills.

Once you’re done, screw the radiator cap back in place tightly and then start your engine for about 10-15 minutes to let it circulate. Turn off your engine and check the coolant level to be sure it is appropriate.

– Fix Water Pump Leak

One of the quickest fixes for rust in your coolant is to fix the damaged water pump as soon as it is diagnosed to be the problem. Fixing a water pump is quite simple and can be done in a few steps once you have the technical skills and tools. First, you should try flushing the coolant system and then draining it of all coolant. Locate the engine belts and take them off gently until you can see the water pump.

Gently take out the water pump bolts with a wrench or screwdriver and remove the water pump itself. Replace the old water pump O-rings and gasket if they have issues before installing a new pump. If this repair proves too difficult for you, you can contact a professional mechanic to do it.

– Use the Right Coolant for Your Vehicle

Another easy way to stop rust from forming on your coolant system is to use the right coolant recommended for your car. You can refer to your car manual guide to find out this information. If you can’t find it there, consult an experienced mechanic who will decide what type of coolant your car needs.

You should also avoid mixing different coolants. These coolants are usually made of different components, so mixing them for your car is not ideal. Once you use the recommended coolant, your cooling system should stop producing rusty water.

– Top Off or Reduce Coolant Level Where Necessary

If your coolant level is low, you should take it up to the proper level by topping it off. Since insufficient coolant can cause your engine to overheat, blow your head gasket and even cause the car to shut down, you need to top it off regularly.

In the same vein, you should also drain out the excess coolant from your cooling system as it can have an adverse effect, especially when it comes in contact with wires. Keeping the coolant at the proper level will prevent rust from forming on your cooling system.

– Bleed Out Air From Radiator

You can fix rust from forming on your coolant or prevent it by bleeding out air from the radiator. Air in the radiator can cause acidic air pockets to form and cause rust, so removing excess air will prevent this. Doing this is pretty simple, although it can be technical if you lack the needed skills and equipment. We recommend seeking the service of a professional mechanic to do this.

– Replace the Worn Coolant

Another way to fix the rust forming in the coolant system is to replace the worn coolant with a fresh one. Once you’re certain your current coolant is past its expiry date, you should replace it with a new one. Make sure you properly drain out the old coolant before refilling the cooling system with the new one. Also, make sure that your coolant is high quality and the right type for your car.

To prevent engine corrosion, first check your coolant level and ensure that it is at the right amount. Make sure you are using the right type of coolant for your vehicle. Also, change your engine oil regularly and pay attention to the fluid level.

Always ensure you use high-quality synthetic lubricants for your engine and lubricate as often as possible. You can also prevent engine corrosion by ensuring that your fuel filters and injectors work perfectly.

– Take Preventative Measures

You can prevent rust from forming in your coolant by checking and topping off the coolants where needed. Also, replace the old coolant and bleed air out from your radiator whenever you work on the cooling system. Your coolant should also contain water laced with a rust inhibitor.

If your car starts to overheat, first turn off the AC unit if it’s on because it could be causing unnecessary strain on your engine. If the AC isn’t turned on, you should park and turn off your engine for a while. Also, check that you have the right amount of coolant, and if you don’t, immediately add more coolant.

Conclusion of Rust in Coolant


Leaving rust to form on your coolant can spell trouble for your engine unless it is fixed. Here are the main points discussed in this article:

  • Rust in coolant is caused by water pump leaks, insufficient or low coolant levels, as well as using the wrong type of coolant. 
  • It can also be caused by using coolant past its expiry date or air trapped in the radiator.
  • You can fix this by flushing out the coolant system and bleeding air out from the radiator. Also, use the right coolant type and maintain the proper coolant level.
  • Flushing the coolant system is something you can do on your own. If you’re not certain how to do this, contact an experienced mechanic.

Now that you know what causes rust to form in your coolant, you shouldn’t waste time fixing this. Keep our tips and tricks handy so you know what to do when you encounter this problem.

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