Head Gasket Failure Symptoms? SUBARU Outback V (BS) (10.2014 - ...)

Yes, coolant loss, a sweet smell from the exhaust pipe and periodic overheating are very likely to indicate a problem with the cylinder head gasket. You should also pay attention to white smoke from the exhaust pipe, emulsion on the oil filler cap or dipstick, and bubbles in the expansion tank. It is recommended that you contact a car service center for diagnosis.

The symptoms you describe on your 2015 Subaru Outback—coolant loss, a sweet smell from the exhaust, and occasional overheating—are indeed classic signs that could indicate a head gasket issue, but they can also be caused by other cooling system problems.

Symptoms Suggesting Head Gasket Problems
- Coolant loss without visible leaks: A blown head gasket can allow coolant to leak internally into the combustion chamber or exhaust system, causing unexplained coolant loss.
- Sweet smell from the exhaust: This often indicates burning coolant, which is a hallmark of head gasket failure.
- Overheating: A compromised head gasket can cause poor coolant circulation or combustion gases entering the cooling system, leading to overheating.
- White smoke from the exhaust: Though you didn’t mention it, this is another common symptom of coolant burning in the engine.

Other Possible Causes of Overheating and Coolant Loss
- Coolant leaks from water pump, radiator, or hoses: These are common and easier to fix than a head gasket.
- Faulty thermostat or radiator fan: These components regulate engine temperature and their failure can cause overheating.
- Radiator or cooling system blockages: Can reduce coolant flow and cause overheating.
- Water pump failure: Some Subaru water pumps have plastic impellers that can fail internally, causing coolant circulation issues.

What You Should Do Next
- Perform a combustion gas test in the coolant: This test detects exhaust gases in the cooling system, which strongly indicates head gasket failure.
- Check for white smoke from the exhaust: This would reinforce the head gasket diagnosis.
- Inspect for external coolant leaks: Look under the car and around the engine bay.
- Pressure test the cooling system: To find leaks or weak spots.
- Check oil condition: Milky or frothy oil can indicate coolant mixing with oil due to a blown head gasket.

Your symptoms could very well be related to a head gasket failure, especially the sweet exhaust smell and overheating combined with coolant loss. However, other cooling system