Have an '02 V70 d5SE that was returning 52.8 mpg. Now 47.5 mpg.
Oil & filter changed at 180,000 miles using "AD-TEC 16" 5 - 30 fully synthetic oil instead of MOBIL 1. Air filter and gearbox oil also changed. Wonder if cold weather adversely impacting?

(PS: NO Facebook account)

 

Certainly cold weather can change your fuel consumption - extra drag in the gearbox/differentials/axles etc but also this may be due to seasonal fuel additives. Check tire pressure?

 

Check tyres weekly. Wheels re-powder coated a month ago so NO leakage there and running 34 psi all round. Added a "Forté" oil flush just before I changed the oil. Keep getting: HIGH EMISSIONS SERVICE REQUIRED message coming up on the dashboard. Car went into limp mode this morning briefly with 11⁰C outside air temperature!

Going to Volvo specialist to have diagnostics looked at again! Car was REGULARLY returning 52.8 mpg, so a significant percentage drop as now 46.5 mpg!

 

May I throw a fiver on "Upstream Oxygen Sensor" to win?

 

definitely cold weather takes more gas, up here in Canada when the winter weather brings -10 or more we see huge mpg decreases.