He is right. You are not above the arctic circle. We have alot colder weather than what you have and in winter it's 10w30 for 5 months (nov-march) then 10w40 for rest of year. fully synth is a waste of money specially on older motors. If you had a high tolerance motor and started from new ok.Just had a huge row with my mechanic, he insists that I need 10W40 and not 5W40.
He reckons the engine is a TDi not a TDCi , fully synth would be to thin.
Opinions Please......