Fuel Preheating by Reverse Running
It does not need large expenditures, just a heat valve and a disrupted fuel return pipe, to prevent fuel in the filter from paraffin expulsion and therewith from blocking at low temperatures. Indeed, the temperatures should not
sink with this system so far that already the fuel which is in the filter at the moment of starting the engine becomes too thick.
Diesel oil can become as hot as 80°C in the fuel injection pump. Because it heats up faster than the coolant, you can use the heat of the diesel oil flowing back to the tank to heat the fuel sucked in. At temperatures below
15°C the red bimetallic leaf operates the check valve and opens the filter for the slightly heated runback fuel. Above this temperature the fuel flows back to the tank for cooling. The intake of stronger heated fuel is
undesirable for the diesel engine. Therefore, modern engines cool the runback fuel, in addition, before it enters the tank.