Why Radiator Keeps Pushing Water Out?


You may have to figure out a dozen probable causes if your radiator keeps pushing water out. Instead of giving up, however, you’ll need to assess potential causation or correlation with any recent changes you have made to your vehicle, especially the radiator components. 

A radiator may keep pushing water out due to a bad cap, trapped air in the cooling system, coolant leak, faulty thermostat, and broken seals or o-rings. Also, you may have a damaged head gasket, leaky heater core, old hoses, and other failing radiator parts. 

A few problems are easier to detect and relatively inexpensive to fix. However, some problems require a professional inspection. In this article, I’ll explain the various typical causes why a modern radiator may keep pushing water out and what you can do to solve these problems.

Why Your Radiator Keeps Pushing Water Out?

Always begin your inspection with the part of the radiator that you think is the triggering factor. Otherwise, the entire inspection can be a long and tedious process. Also, observe the precise circumstances when the radiator keeps pushing water out, like when the engine is overheated. 

Prioritizing the possible triggers can help you eliminate the other common causes explained in this guide. Furthermore, inspect any radiator components that you may have changed recently, such as the radiator cap, thermostat, coolant, or seals. 

1. You Have a Bad Radiator Cap

The radiator cap is also a valve, which regulates the pressure at the radiator filler neck. Thus, a properly functioning radiator cap should keep the coolant inside the unit, not let it leak, bubble up, or gush out. 

A radiator cap’s valve allows excessively hot liquid coolant to rise to the filler neck and flow into the overflow tank. This process reduces the pressure inside the radiator and the coolant’s temperature. 

However, a bad radiator cap won’t contain the hot fluid inside the pressured unit.

How To Fix?

You must replace a bad radiator cap. Match the part number and check the pressure rating before you buy a new radiator cap so that you don’t have the same problem again. Fortunately, this solution is inexpensive and straightforward, but unfortunately, your problem may be elsewhere.

Read: Why Radiator Fan Goes ON and OFF?

2. The Cooling System Has Trapped Air

One reason that radiator caps fail is through overheating. 

A super hot coolant due to leakage or engine overheating exerts more thrust on the radiator cap than it can endure. Since the valves have a pressure rating, the radiator caps will fail when the force is greater than the threshold. 

Another reason for these caps failing and a radiator pushing water out is trapped air in the cooling system. The entire cooling system, including the radiator, is a sealed and pressurized unit. 

The various valves, inlets, and outlets function optimally in the expected pressure range. 

Trapped air inside the cooling system and radiator will alter the pressure. Also, the lighter air pockets compared to the coolant fluid rise to the radiator filler neck. Now, the cap’s valve is engineered to regulate the coolant flow, not compressed air, which means that you may have a problem.

How To Fix?

The solution to eliminating trapped air pockets from the cooling system and radiator is known as bleeding. All you need is a spill-free funnel. However, this remedy will work only if everything else about your radiator is alright. 

Here are the steps to bleed your vehicle’s radiator:

  1. Allow the engine to cool down to room temperature.
  2. Open the radiator cap and install the spill-free funnel.
  3. Start the engine and let it run for a few minutes. 
  4. The pump will circulate the coolant and the trapped air.
  5. Some coolant and water will pop up inside the funnel.
  6. The trapped air will rise, form bubbles, and escape.
  7. Stop the engine when there’s no noticeable bubbling. 

Ideally, you should use the bleeding method whenever you refill the coolant or interact with the radiator. Trapped air pockets don’t create major issues immediately, so you won’t know that the pressurized and sealed cooling system is compromised until there’s an evident problem. 

Read: Why Radiator Fan Always On?

3. The Radiator Thermostat Is Faulty

Like the pressure-rated cap, the radiator thermostat has a valve designed to regulate coolant circulation inside the system. Essentially, the thermostat keeps the coolant circulating through the engine until the fluid breaches the maximum operating temperature. 

At this point, the valve of the thermostat allows the super hot coolant to flow out to the radiator. 

A faulty thermostat won’t regulate the coolant’s circulation as intended. Suppose the valve in the thermostat opens too late when the coolant is much hotter than it should be. This super hot coolant will exert unusually high pressure on the hoses, seals, and the radiator cap’s valve. 

Thus, the cap may fail, your radiator will push water out, and you may have other problems.

How To Fix?

You need to replace a faulty thermostat. The typical thermostat isn’t expensive unless you own a sports car, and you can replace it yourself. However, ensure you buy the right thermostat for your vehicle and install it correctly. Otherwise, you may have the same problem again. 

Read: Why Radiator Fan Is Not Working?

4. The Radiator Has a Coolant Leak

Coolant leakage causes overheating, so you’ll have hotter fluid in the radiator exerting more pressure at the filler neck under the cap. Also, if the coolant volume in the system is low, it’s a telltale sign of a leak, because a sealed system shouldn’t lose coolant without any leakage. 

Coolant may leak due to the following reasons: 

  • Bad radiator cap.
  • Worn thermostat seal.
  • Broken water pump seal.
  • Worn or damaged hoses.
  • Leakage in the heater core.
  • Cracked radiator. 

How To Fix?

The solution depends on what you find during the inspection. Accordingly, here are your options:

  • Replace the faulty radiator cap, broken seals, or old hoses. 
  • Use a sealant to fix leakage in the radiator or heater core.
  • Consult your mechanic to fix significant leaks and cracks. 

Choose a premium-quality sealant if you opt for a DIY solution. A sealant shouldn’t have much residual buildup inside the cooling system. Otherwise, you may have an unpleasant clog inside the radiator. Also, contamination may impair the efficient functioning of the coolant and radiator.

Read: Radiator Fan Replacement Cost

5. The Head Gasket Is Damaged

A cracked or damaged head gasket will compel the radiator to keep pushing water or coolant out. A tiny or pinhole crack may be repairable but significant damage is usually beyond the sealants you can buy online. 

Here’s how you can gauge the extent of head gasket damage:

  1. Allow the engine to cool so that you can safely remove the radiator cap.
  2. Remove the radiator cap, start the engine, and wait for some time. 
  3. Observe the bubbles forming at the radiator filler neck. 
  4. Small and sporadic bubbles imply a pinhole crack on the head gasket.
  5. Medium-sized and consistent bubbles indicate substantial damage. 
  6. Overflowing water or foamy coolant at the radiator filler neck means critical damage.
  7. Also, you may check if the engine oil is milky, which might mean it’s contaminated with the coolant. 

How To Fix?

You may use a sealant like this Bar’s Leaks Blown Head Gasket Repair (available on Amazon.com). This bestselling sealant can fix a blown head gasket, cracked cylinder head or block, heater core, and other leaks in the radiator. 

However, such sealants may work only on small and other moderate cracks or damages. You may have to replace the head gasket if it’s damaged beyond the scope of such a solution. 

Read: Why Car Overheats?

6. Your Radiator Is Past Its Prime

Last but not least, your radiator may keep pushing water out if it’s past its prime. Radiators wear out in time, the heater core may corrode, detritus buildup can cause clogging, and the tubes and fins might become ineffective. As a result, your engine will overheat, so will the coolant. 

How To Fix?

It’s not practical to generalize if a specific radiator is beyond repair. You have to decide based on your assessment after checking for all other problems. Generally, an unusable radiator is the last pitstop if nothing else is causing water, coolant, and possibly some engine oil popping out.

Final Thoughts

Don’t use tap water to compensate for coolant leakage or loss. Also, don’t top up coolant before locating and fixing all the leaks in the system.

Furthermore, avoid diluting the coolant to the extent that its boiling point drops significantly, even if you use distilled or deionized water. Otherwise, you’ll defeat the coolant’s purpose, and the radiator may keep pushing water out without any other problems.

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