How Can I Tell If I Have a Coolant Leak?

What’s that Sweet Smell Coming From My Car?

If you smell a sweet smell coming from your car, your car might be leaking coolant. Learn how to find a coolant leak with and without a pressure tester to find out why your car smells sweet, how to find where the coolant leak might be, and how to fix it.

What Does a Coolant Leak Smell Like?

Leaking coolant, also known as antifreeze, can smell sweet like maple syrup or burnt marshmallows. It can happen inside or outside the car and might mean there’s a coolant leak. If you smell a sweet smell coming from your car, these steps describe how to find a coolant leak.

How to Find a Coolant Leak Without a Pressure Tester

Mechanic’s Tip: Different vehicles have different designs. Follow any hoses in the coolant system and inspect all of them for leaks or damage

1. Check for Coolant Puddles

Check under the vehicle for coolant leaks. The puddle’s location may help lead to the leak.

2. Check the Coolant Level

The coolant level in the coolant reservoir should be near the cold or hot marking if there are no leaks. If the level appears low, there is likely a leak.

3. Inspect the Upper Radiator Hose

Check along and at the ends of the upper radiator hose for leaking or crusting. The hose should feel firm and soft but not collapsed or brittle.

4. Inspect the Thermostat Housing

Follow the radiator hose down to the thermostat housing. If the thermostat housing has an air bleeder, check the O-ring for leaks. Check the gaskets on the thermostat housing where it connects to the engine block.

5. Examine the Water Pump

Check the water pump and the hose that connects to it for leaks. Use a mirror and a flashlight to inspect the bottom of the water pump and the gasket for traces of fresh or dry coolant.

6. Examine the Heater Core Hoses

Follow the heater hose that leads to the heater core in the firewall. Inspect the ends of the hoses that lead to the firewall for signs of leaking.

7. Check the Radiator

Check the hose connections to the radiator and the seams on the radiator for looseness or leaking.

8. Check the Radiator Cap (with the System Cool)

With the system cool, remove the radiator cap and check the coolant level in the radiator, which should be near the top. After a certain amount of years and mileage, the radiator cap can fail. The caps have a spring and are supposed to release pressure. If the cap’s spring or gasket/seal starts to fail, it can release steam. This is usually not visible but it can smell sweet. A weak seal or spring will release more pressure faster than usual, making for a more pungent smell.

Fix a coolant leak yourself with quality auto parts at

How to Find a Coolant Leak with a Pressure Tester

If you find no signs of leaking after checking the parts of the coolant system, you can test the system with a pressure tester. Local parts stores may loan tools, and you can also buy a new one or have a mechanic pressurize the system.

Before looking for a coolant leak with a pressure tester, wait for the vehicle to cool down

  1. Remove the Radiator Cap

    With the vehicle cool, remove the radiator cap from the radiator

  2. Attach the Pressure Tester to the Radiator

    Place the pressure tester on like a radiator cap until it’s secure, and use an adaptor from the pressure tester kit if necessary

  3. Set the Pressure on the Gauge

    Pump up to set the pressure on the pressure gauge between 15-20 psi to reach the psi on the radiator cap. Do not go over this number

  4. Monitor the Pressure

    Watch the pressure gauge—the faster the gauge drops the bigger the leak. If the system is holding pressure at the set pressure and there is no sound of leaking, check the gauge about every 5-10 minutes for 30 minutes and see how much the pressure has dropped. It is at normal pressure if the pressure doesn’t drop significantly after 30 minutes.

This article reviews to steps for using a pressure tester in more detail.

Test the Radiator Cap

  1. Press the radiator cap to a pressure tester until it locks
  2. Connect the tester to the gauge
  3. See if the gauge reaches the same pressure as the psi rating for the radiator cap, which is usually marked on the radiator cap
  4. If the radiator cap can’t reach pressure or loses pressure very quickly, the spring or seal is defective and the radiator cap needs to be replaced
  5. If the radiator cap is working, it will slowly and smoothly release pressure

Repair a Coolant Leak Yourself with 1A Auto’s Videos

Replace coolant system parts yourself with 1A Auto’s how-to videos that cover many years, makes, and models.

Parts to Fix a Coolant Leak Mentioned in This Article

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Sweet Smell from Your Car? How to Find a Coolant Leak - 1A Auto
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Sweet Smell from Your Car? How to Find a Coolant Leak - 1A Auto
If you smell a sweet smell coming from your car, your car might be leaking coolant. Learn how to find a coolant leak with and without a pressure tester
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1A Auto
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