Hi everyone,

My car is currently at the mechanic, and he says it has a head gasket failure.
I’m not fully convinced, so I’d really appreciate your opinions.

Symptoms:

• The car starts to overheat after some time, never reaching the “H” mark but getting quite close.
  
• It only overheats during long drives — for example, continuous 100 km trips on the highway, especially when pushing it a bit.
  
• In city driving, even with frequent full-throttle runs, the car never overheats.
  
• It loses coolant, but only small amounts.
  
• No smoke or “sweet” smell when accelerating.
  
• No noticeable power loss.
  
• When it starts heating up, if I turn on the heater, the temperature usually drops — but sometimes the heater blows cold air instead of hot.
  
• A Subaru specialist said it’s a head gasket failure, but there are no bubbles in the coolant or other typical HG failure symptoms.
  

Additional info:

• The thermostat was replaced, but the problem persists.
  
• No visible coolant leaks.
  
• The car runs on LPG (BRC system), which uses coolant from the radiator to heat up before switching from petrol to gas. Could this connection be leaking internally?
  

Car details:

• Subaru Impreza GT Turbo EUDM (1998)
  
• Engine: EJ207 from a Subaru STI Version 7
  
• LPG system: BRC
  

 

The lost coolant is going somewhere.
You say that there are no bubbles in the cooling system, have you had the cooling system "sniff tested" for combustion gases to rule out the HG allowing them into the water jacket?