Heating diesel to coolant temp shouldn't be a problem as it is still well below the flashpoint and it is also contained in the fuel system without exposure to air (oxygen) so there should be very little issue with accidental ingition. An effective coolant heat exchanger should have no problem heating the blend to coolant temp. My only reservation would be the returning of the heated diesel to the stock fuel tank. Driven long enough you would have a pretty hot fuel tank which would be filled partially with air. This could lead to problems and maybe even condensate issues over time. Just a thought... RT

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