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How do I Fix an Antifreeze Leak?

By Ron Marr
Updated Feb 01, 2024
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The one good thing about an antifreeze leak is that it makes itself apparent very quickly. Your temperature gauge soars, warning lights comes on, and sometimes steam pours from beneath the hood of your car, truck, or SUV. When these things occur, pull to the side of the road and stop the car as soon as safely possible. Continuing to operate a vehicle that has lost its coolant can easily lead to the destruction of its engine.

An antifreeze leak can be either external or internal. If you are experiencing an internal leak, something like a bad head gasket or a cracked engine block, it is best to have the vehicle towed to a mechanic. A broken head gasket or cracked engine block may be leaking antifreeze into a cylinder or your oil crankcase. These are not simple repairs, and will often cost well over $1,000 US Dollars (USD).

An external antifreeze leak is easier to diagnose and repair. First, you should determine where the leak is occurring. The most common sources of leakage are the upper or lower radiator hoses, the radiator cap, the radiator overflow reservoir, or within the radiator itself. Leakage can also take place around the water pump, heater core, and intake manifold gasket.

To diagnose and repair an antifreeze leak, first check the radiator cap. If you are very lucky, and cannot spot any other leaks, then the problem may simply be that the cap has been damaged and is unable to contain the pressure of the hot coolant in the radiator. The solution is to buy a new cap. Remember to wait until the car has cooled before removing the old cap, as a facefull of boiling antifreeze is a less than pleasant experience.

Next on the list is a check of the upper and lower radiator hoses and hose clamps. You should easily be able to tell if a hose is cracked or split, as the coolant will either be dripping out or spurting like a fountain. Replacing the upper hose is a relatively quick job. Replacing the lower hose is often a difficult and dirty task. If the hoses appear to be fine, check the clamps.

Like all mechanical parts, hose clamps can weaken and loosen over time, leaving tiny gaps and spaces around intake and outflow openings. Just replace the clamps with new ones. Replacement of the upper hose clamps is a breeze, as they are easily accessible. Again though, due to the cramped engine compartments of virtually all late-model cars, replacement of the lower hose clamps may lead to scraped knuckles and cursing.

The next most common source of an antifreeze leak takes place in the radiator itself. You can try the quick fix, which is to pour in a can of one of the many additives that profess to stop pinhole radiator leaks. Sometimes this will work, and sometimes it won’t. A radiator can be damaged by internal corrosion, flying rocks or debris, and sometimes simply by age itself. In any case, an additive repair is usually a temporary solution, and eventually your radiator will either need to be repaired or replaced by a professional.

The final simple repair for an antifreeze leak lies in your radiator’s plastic overflow reservoir. This reservoir takes in coolant when it becomes too hot. After it has cooled, it is sucked back into the radiator. If there is a hole or crack in the reservoir, you will lose coolant on a regular basis. The choices are either to try and repair the crack or hole with glue, or purchase a new reservoir.

Fixing a leaking water pump, heater core, or intake manifold gasket is more complex. Unless you are a qualified mechanic, they fall into the “don’t try this at home” category. The odds are, unless you are very knowledgeable in automotive repair, you will cause more damage than already exists.

WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

By Glasshouse — On Sep 03, 2010

@ ValleyFiah- It can be hard to diagnose a blown head gasket or cracked head/block. The only way to know for sure is to physically inspect the head and gasket.

However, there are a few telltale signs that can give clues to the health of your head gasket. Blown head gaskets often lead to oil leaking into the coolant, or coolant leaking into the oil. Milky colored oil, sweet smelling exhaust, or white smoke/steam coming from the tailpipe are all signs that there is water and coolant in the oil. White crust around the coolant filler cap, and oily coolant are signs that oil is leaking into the coolant. Bubbling coolant, low compression in a couple cylinders, or missing and rough idle can also point to a blown gasket or warped head.

By ValleyFiah — On Sep 03, 2010

How do I know if I have a blow head gasket?

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