Engine Coolant Leaks – How To Find Them – External And Internal

Engine Coolant Leaks - How To Find Them - External And Internal
Engine Coolant Leaks - How To Find Them - External And Internal

Checking your cooling system for engine coolant leaks, is easier than you think.

So, engine coolant leaks can happen, anywhere in the cooling system.

Fortunately, nine out of 10 times, engine coolant leaks, are easy to find.

So, the first sign of engine coolant leaks, is usually an engine showing, a low coolant level.

Consequently, this is followed by, a high engine temperature reading or actual engine overheating. Usually, the coolant can be seen dripping, spraying, seeping or bubbling, from the leaky component. Antifreeze is a concentrated product, normally based on glycol and containing inhibitors.

As a result, it has to be diluted, to a suitable concentration for use. The diluted liquid, is usually called coolant.

So, if you suspect the vehicle has a coolant leak, visually inspect the engine and cooling system. Look for any sign of liquid leaking, from the engine, radiator or hoses. Consequently, the color of the coolant may be green, orange or yellow. All depending, on the type of antifreeze in the system.

You may also notice, a sweet smell, which is a characteristic odor, of ethylene glycol antifreeze. First of all, you need to know, what type of engine coolant leaks you have.

There Are Primarily, Three Places You Can Have, Engine Coolant Leaks:

  • External leaks
  • Internal leaks
  • Leaky rad caps

Finding, External Leaks

External Engine Coolant Leaks
External Engine Coolant Leaks

External leaks, are the easiest type to find. Because, most of the time you will just, visually see them.

The source may be:

  • Rad hoses
  • Water pump
  • Freeze plugs
  • Heater core
  • Radiator
  • Overflow tank
  • Cracks in the engine block, cylinder head, intake manifold
  • Blown head gasket, that is leaking externally

Internal, Leaks

Internal Engine Coolant Leaks
Internal Engine Coolant Leaks

An internal leak, would be apparent when the coolant level, does not stay constant. And, you find that you need to, constantly refill the tank or your engine overheats.

The source of internal leaks, could be the fault of:

Rad Cap, Leaks

Rad Cap Engine Coolant Leaks
Rad Cap Engine Coolant Leaks

So, if you have a leaky, weak or damaged radiator cap, you may experience loss of coolant. This could also create, an air lock in the radiator as well.

Other Things Could Be:

  • The cap, is not fitting property
  • If the cap, is the wrong cap for the radiator

This will also cause, pressure loss and engine coolant leaks.

SAFETY FIRST: Do not open the radiator cap while the engine is hot! Even if the cooling system is leaking, the coolant will be under a lot of pressure. Especially, if it is low and coolant is boiling inside the engine. Shut the engine off and let it sit about an hour, so it can cool down. Then, place a rag over the radiator cap and slowly, turn the cap until it starts to release pressure. Wait until all the pressure has vented, before turning the cap, the rest of the way off.

How To Check, Your Cooling System For Leaks:

Using A, Leak Detection Dye

Using A Leak Detection Dye
Using A Leak Detection Dye

Adding leak detection dye to the coolant, can make a slow leak easier to find. Most auto parts stores, sell UV dye and light kits. So, you can add the UV dye to your engine cooling system. Then drive your car for a few days, to make sure the dye circulates through everything. Then, park your car in a very dark place and use the UV light, to search for your leak. The dye will show up, very brightly under the UV light. As a result, show you a path, to your engine coolant leaks.

Pressure Testing, The Cooling System

There are several ways to find out whether or not your cooling system, is holding pressure. So, top off your cooling system, tighten the radiator cap and start the engine. When the engine reaches normal operating temperature, turn on the air conditioner. Consequently, (to increase the cooling load on the system) and or take it for a short drive. Then check the radiator hoses and water pump, for seepage or leaks.

Radiator, Pressure Testing Pumps

Coolant System Tester
Coolant System Tester

This tool is nothing more, than a little hand pump. It comes with a combination vacuum pressure gauge and a fitting, that is attached to the radiator filler neck. To check for engine coolant leaks, attach the tool to the radiator and pressurize the radiator.

Furthermore, if you have a radiator cap that says 12 pounds, you pressurize the radiator to 12 lbs. Then, wait to see what happens. If there are no leaks, the system should, hold pressure for 10 to 15 minutes. But, if it does not hold pressure, the system is leaking. So, if you cannot see any visible leaks on the outside. Then, it means the leak is inside the engine.

Internal Engine Coolant Leaks, Are The Worst Kind:

Cylinder Head Gasket, Leak Testing

Block Leak Tester
Block Leak Tester

A block checker, is another tool that can be used, to detect a leaky head gasket. The gas sensitive blue liquid, changes color, if there are any, combustion gases, in the coolant system.

Topping Up, After Repairing Engine Coolant Leaks

When refilling the cooling system after making a repair, always use a 50/50 mixture of antifreeze and water. Never use straight water. Because, it has no freezing protection, no corrosion protection and it boils (212 degrees F.) But, a mixture of antifreeze and water (which protects to 240 degrees F.)


Finally, the best way to avoid, low coolant levels, is to regularly check your coolant level.  And, once you’ve discovered a leak, you need it repaired ASAP. Finally, this will help stop overheating and major engine damage.

Thank You !