Old timer tells me he mixes heating oil with diesel

Talking to a guy today who has worked with and drove diesels for yrs and he has a e320 cdi 2007 from new with 88000 mls and he told me he puts 10 ltrs of heating oil into every 60 ltrs of diesel every winter he said the car runs better ,starts easier and stops the diesel getting thicker as the temperatures drop below zero. ,, this guys is a young 70 yr old .
who am I to argue with him but not sure what to think.

What's your guys,girls thoughts on this ?