Engine Coolant Leaks – How To Find Them – How Bad Are They

Engine Coolant Leaks - How To Find Them - How Bad Are They
Engine Coolant Leaks - How To Find Them - How Bad Are They

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 indicator. As a result, 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 colour 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 odour 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 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 engine block, cylinder head, intake manifold
  • Blown head gasket leak externally

Internal Leaks

Internal Engine Coolant Leaks
Internal Engine Coolant Leaks

An internal leak would be noticeable, 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:

  • A cracked block
  • Cracked cylinder head
  • Leaking intake manifold
  • Blown head gasket

Rad Cap Leaks

Rad Cap Engine Coolant Leaks
Rad Cap Engine Coolant Leaks

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

Other Things Could Be:

  • The cap is not fitting property
  • If the cap is the incorrect 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 considerable 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. 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, providing a path to your leak point.

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 to the pressure rating on the radiator cap.

For example, if you have a radiator cap that says 12 pounds; you pressurize the radiator to 12 lbs. and 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. Finally, if you cannot see any visible leaks on the outside; it means the leak is inside the engine.

Internal Leaks Are The Worst Kind:

  • A blown or leaking head gasket
  • Cracked cylinder head
  • Leaking engine block

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 colour, 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; either by lowering coolant levels or from evidence of a leak, you need it repaired ASAP. As a result, this will help stop overheating and major engine damage.

Thank You !