I had a 1963 Mercedes-Benz 190D with the original owner's manuals.

The engine was an 2.0 liter OM621-III diesel.

In the section on winter driving it actually advises you to mix kerosene with the diesel if it gets very cold - in order to help avoid freezing of the fuel.

Up to 50% by volume kerosene could be added if needed.

It also said you could not do this in Britain due to TAX reasons.

This was an ancient diesel engine with very sensitive fuel injection equipment.

If the manual actually recommended it, you can draw your own conclusions.

Sincerely,

Dusky Lim