2010 Subaru Forester - Fuel mileage dropped by 10% or so - Why?

Maintenance/Repairs
21

It could be your thermostat is stuck open.

22

For the third time in the thread. LOL.

1 Like
23

Well, just count it as another vote. I scanned this pretty quickly.

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24

No, the ethanol content is not always displayed, however, I believe it is normally 10% at the stations I go to.

I understand that 15% ethanol would not provide as good mileage. Thanks.

25

There seems to be a consensus that a likely fault is the thermostat. My inclination is to flush and refill the cooling system and replace the thermostat. Thanks.

26

I wouldnā€™t call it a consensus. Just one of the possibilities. No one can diagnose by internet. Although, just as a matter of maintenance, Iā€™d never tell anyone it was a bad idea to service the cooling system/thermostat. So Iā€™d go ahead. But not assume it will necessarily fix things.

Do you have any manner or check engine/service engine light glowing on the dash?

2 Likes
27

There are no OBD error codes, nor check engine/service engine indications on the instrument panel.