My Volvo's XC60 2010, t6, fuel efficiency in city suddenly decreased it now consumes 2-3 liters more than it used to be. However, on highway the consumption stayed the same. Had it checked with computer diagnostics and nothing appeared to be wrong. I was told that it could be a thermostat (which still works but not doing its job as it used to be). Has anybody had the similar issue and what could be the reason?