How Does a Radiator Burst?

by Cayden ConorUpdated July 06, 2023

Defining the System

A radiator is a non-pressurized system when cool, but when it gets hot it becomes a pressurized system. You can easily check the radiator fluid level when it is cold, but if you check it when hot, you will most likely be burned by the hot water and antifreeze mixture.

Radiator Function

A radiator cools water in the vehicle. The water pump circulates water through the engine and radiator. The water picks up heat in the engine and is cooled in the radiator. There are two hoses between the radiator and the engine. The top hose is connected to the engine via a thermostat housing. The thermostat is what determines the reading on the temperature gauge on the dash. If the vehicle does not have a gauge, it will have a “dummy light.”

Lines In and Out

The radiator also has two small metal lines attached to it: one going into the radiator, one going out. They lead to the transmission. If you do not have a separate trans-cooler, the radiator acts as a cooler for the transmission fluid.


The radiator is also equipped with one or two fans to help the cooling process. They may be electric fans attached directly to the radiator, or you may have one manual fan that is attached to the water pump.

Cause of a Burst

There are a few things that can cause a radiator to burst. If too much pressure builds up, it can cause a weak spot in the radiator core or tank to give way. Too much pressure can be cause by a clogged radiator (lime build up), a restriction in the system or a bad radiator cap. The radiator cap is designed to release pressure.

Damage to the Tank

Some radiator tanks are made from plastic. Because of the amount of heat the radiator is subjected to on a daily basis, these tanks eventually wear out and may crack.

If you run over rocks or other debris in the roadway, and the tires kick it up, it can hit the radiator and will either crack the tanks or damage the metal fins in the radiator, causing a leak.

Water Leaks

If a radiator leaks all the water out, the vehicle will overheat. Once the vehicle overheats, it could cause other engine damage. The engine may lock up and stall the car. If you have aluminum heads, the heads may warp. They could warp just enough to create a hole in the gasket, or they may warp to a point where they will need to be milled or replaced. Either way, it’s an expensive job.

Preventing Overheating

If you notice the water gauge getting up into the red, or if the dummy light comes on, stop immediately and shut the car off to try to prevent further overheating. The car must cool for at least one-half hour before you attempt to open the radiator cap (unless you want to get sprayed with boiling water and antifreeze).


There is one major warning that most people do not realize. If all the water leaks out of the radiator, there is nothing for the coolant temperature sensor to sense, and your gauge will not read properly. It will read as if the car is completely cool. It is pertinent to check the radiator at least once per month for the correct water level.

Video showing what causes a radiator to burst:

Comments on this video:

  • So if the radiator blew and my new hoses are swollen thats a red flag right? I took the top rad hose off to the engine and it appears to have an oily film inside
  • If my ratiator cracks all the way through should I spend the money to fix or do you think the crack cause something else like a warped head or something else?

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