[oil pan 4]

70km may sound like a way more time then what is needed to warm up a vehicle but I have seen posts on here where people have found that they don't get their best fuel economy until after the engine oil and transmission fluid are up to full operating temperature.
Some of our members have made observations showing that it can take as long as 30 to 35 km to bring a car's engine oil and transmission up to full temperature.
These were on gasoline engine cars with no engine coolant to oil heat exchangers.

The reason why fuel heating doesn't tend do anything beyond initial warm up is because the diesel injectors are screwed into the cylinder head. So the injector and the fuel getting sprayed through it is going to be the same temperature as the cylinder head.

Out of all the diesel manuals I have read, all of them do not recommend using "cold air" if that cold air is below freezing to -10C. At that point they recommend drawing the air for combustion from inside the engines enclosure. The engines talked about often did not have intercoolers.

Another thing I have noticed with diesel cars is they tend to take longer to get to operating temperature then struggle maintaining operating temperature.
They are just too efficient for their own good sometimes.

Do you not have any way to plug in a engine block heater?