Subaru Engine Light + Heat Loss Points to Bad Thermostat

Had a similar issue with my 2014 Subaru Impreza. The car heating problems turned out to be connected to multiple issues in the cooling system. Main symptoms matched yours: Poor heat output, Performance dropped at idle, Check engine light activated The root cause was a failed thermostat and a small coolant leak near the heater core connection. The coolant level was gradually dropping, causing the heating system to work inefficiently. The check engine light came on due to the engine running hotter than normal. These symptoms often indicate: 1. Low coolant level 2. Stuck thermostat 3. Clogged heater core 4. Faulty water pump 5. Damaged car valve in the cooling circuit Quick checks anyone can do: Check coolant level when engine is cold, Look for coolant puddles under the car, listen for gurgling sounds from the dashboard, Feel both radiator hoses while engine is warm (should be equally hot) This was a serious issue requiring immediate attention, as continued driving could have led to engine overheating. The repair involved replacing the thermostat, fixing the coolant leak, and performing a complete cooling system flush.

Thanks for the detailed reply about the cooling system issues. My Pleo ended up having similar problems with a blocked heater core and faulty water valve. Got it fixed last month but wondering if the repair cost was reasonable. Would you mind sharing how much you paid for the thermostat replacement and system flush? Also curious if you have had any heating problems since the repair was done. My car is running better now but I want to make sure I am staying on top of potential issues with the cooling system. The car heating seems fine for now but I keep checking the coolant level just to be safe.

After getting my Impreza repaired, all heating problems completely disappeared. The mechanic found a broken water valve connection, which was causing the engine coolant to circulate incorrectly. The repair cost was 95€ to fix the cable connection on the valve component. The cooling system has been working flawlessly since the fix, no more issues with poor heat output or temperature fluctuations. Regular coolant level checks are smart preventive maintenance. Your repair approach sounds thorough, addressing both the heater core blockage and valve issues. Based on your description, your Pleo repair likely had more extensive work done compared to mine, as my issues were limited to just the faulty valve connection. Monitoring coolant levels is definitely a good practice to catch any potential cooling system problems early. The original thermostat and system flush prices from my repair would not be relevant now since that was several years ago, but your proactive maintenance approach should help prevent major cooling system failures going forward.

After reading through the symptoms and recommendations, I decided to take my Pleo to a new mechanic who specializes in heating and cooling systems. The initial diagnosis showed both a blocked heater core and a faulty water valve in the cooling system, just as suspected. The total repair came to 420€, which included: Heater core cleaning service, New water valve installation, Complete cooling system flush, Fresh engine coolant While the cost was higher than expected, the improvement in car heating performance has been significant. The check engine light is now off and the heat works perfectly, even when idling. The mechanic showed me the old clogged components and explained how they were affecting the engine temperature regulation. The new shop was much more professional than my previous mechanic. They provided detailed explanations and showed me the actual parts they replaced. Definitely keeping them for future repairs. Just wish I had found them sooner before the car heating got so bad. Since the repair three weeks ago, I have been checking the coolant level regularly and everything stays consistent. No more worrying about engine overheating on my daily commute.