What Do You Do About a Cracked Radiator

The radiator on your vehicle is an essential part of the cooling system and, if damaged, needs to be repaired for proper engine function. A running engine produces large amounts of waste heat, due to the thousands of explosions happening per minute in the cylinders. Your water pump circulates coolant fluid through cavities in the engine and then hoses direct the hot coolant to the radiator, where multiple small pipes with fins attached allow the heat to dissipate in the moving air as the car moves forward, or as a fan pulls airs through the radiator if the car is stationary. 

What Causes a Cracked Radiator? 

There are a few different circumstances that can lead to a cracked or leaking radiator, and some of them can be avoided with proper maintenance. Modern radiators are a bit different than the copper/brass radiators of old. Modern radiators are made of an aluminum core, with 2 plastic tanks on each side that are pressed on. These tanks have a rubber gasket that seals them to the aluminum core. While a number of things below can cause a radiator crack or leak, the main culprit of failure is two-fold – constant road vibrations, coupled with constant thermal cycling of hot/cold over years of driving. Over time, the gaskets and side tanks get weak, and coolant will begin to seep from these mating surfaces. While there are other issues below that can speed this failure, a good majority of radiators will start their failure very slowly – a small leak or crack begins to seep, and gets worse, and worse.  

An overheating engine can lead to radiator cracks, because of the excess pressures and heat that result. If your engine thermostat is faulty, it can fail to circulate coolant properly and contribute to overheating, or be caused by over-heating itself. A leaking head gasket is another issue that can lead to an engine overheating. If your head gasket is leaking, it means that coolant may be making its way into the combustion chamber, or into the engine oil, neither of which are good. 

Poorly maintained engine coolant is another factor that can block a radiator, crack it, or cause over-heating. Modern coolant is designed to have a service life of five years or 100,000 miles, whichever comes first, so you should flush it at that interval or the interval that is recommended in your owner’s manual. Older coolant will contain dirt and debris that it has picked up throughout the years and that can lead to a plugged or cracked radiator, and older coolant loses its ability to fight corrosion, leading to decay from the inside.  

Extreme temperatures can cause radiator cracks as well. If you live in a hot climate, you have a greater risk of overheating the engine, which can lead to cracks or leaks in the radiator. If you live in a cold climate, you must ensure that your engine coolant has the correct ratio of water to coolant concentrate or else the coolant can freeze inside the radiator and rupture the tubes. 

Finally, road debris or an accident can cause cracks in a radiator. The front of your vehicle is designed to offer some protection to the radiator, but it’s not unheard of for small rocks or objects to make their way to the radiator and cause a crack.

Symptoms of a Cracked Radiator 

If you can catch a cracked or leaking radiator early it may save you a lot of trouble down the road, so keep an eye out for these signs of a bad radiator. 

1. Engine Overheating

If you notice that your engine is starting to run hot, it might be a sign that you have a problem with your radiator. It can also be a thermostat issue, so you might want to check or replace that first to see if it solves the problem, especially if it is in an easy to reach location. Thermostats are usually inexpensive, so it won’t cost much to try.

2. Coolant Leaks

If you notice coolant pooling on the ground under your car after it’s been sitting for a while, or if you can see leaks on the radiator itself, it’s time to address a cracked radiator.

3. Sludge in the Coolant

If you open your coolant reservoir and notice that the coolant is discolored, that can also be a sign of a bad radiator. A crack internally between the engine oil cooler and the coolant side can cause them to mix. Coolant that is in good shape should have a clear, translucent color, and depending on the brand, it can be pink, orange, blue, or green. If you notice that the coolant looks murky or has sludge in it you should definitely do a radiator coolant flush and then monitor it going forward, in case the radiator is cracked and depositing gunk into the coolant.

4. Low Coolant

If you notice that your coolant reservoir is low and seems to be losing coolant after being refilled, you may have a leak in the radiator. Do a visual inspection and check under the vehicle for spotting. Sometimes, coolant from a slow leak can dry before it hits the ground. It’s evident with fuzzy pastel-colored deposits.

Can a Radiator be Repaired? 

It is possible to repair a cracked radiator if the crack is small enough, but it’s important to remember that your radiator is subjected to high temperatures and pressure during normal operation, so the product you use must be designed for that environment. 

If you have a small leak, but you can’t find the exact location, it may be possible to use a Stop Leak product that operates in the same way as your blood platelets. You pour it into the cooling system and allow it to run through the leaks. As it is exposed to the outside air, it congeals and forms a barrier that stops the leak. 

If you can locate the crack in your radiator, you can use an epoxy-resin sealer that you apply directly to the exterior of the radiator to seal the hole. For plastic radiators, there are also products that fill the crack and melt into the original plastic, for a very durable finish. 

A woman showing how to install a radiator by sliding it into the front part of her car.

When Does a Cracked Radiator Need to be Replaced? 

If you have tried to use a stop leak product or located a crack and used a sealant on the exterior, but the radiator still leaks, it may be time to replace the radiator. It’s possible that there are additional cracks where you can’t see them, or that the damage to the radiator is too grave to repair. In those cases, a radiator replacement may be your best option. 

How to Remove and Install a Radiator for Repair or Replacement 

You might come to the point where you have tried to repair a cracked or leaking radiator without success and you need to replace it, or you need to take the radiator out of the vehicle to do the repair. If that’s the case, begin by removing the negative battery cable and allow the engine to cool before draining the coolant from the radiator. Working with the cooling system on a hot engine can lead to serious injuries. The drain cock will be a valve on the bottom of the radiator. You can open the cap at the top of the radiator to allow air into the system for better drainage. There will be an input and an output hose that brings coolant to and from the engine. Disconnect those hoses and you may need to remove your cooling fan and other accessories to access the radiator, as well. Remember all the steps you take to remove the radiator and when reinstalling, go in reverse order. 

If you need Trustworthy Advice or the right parts to get the job done, AutoZone has it. If replacing the radiator is too big of a job, take a look out our Preferred Shops in your area, that can help you with your repair!

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