Heated Fuel Filter
Wednesday, February 24th, 2010
Several years ago, during the intitial rebuild, I bought a heated fuel filter for a pound at Old Sodbury. It is made for the Bosch filter units used on Tdi engines and is used by Land Rover on Artctic spec vehicles, and is just a sandwich plate that fits between the standard filter housing and filter cartridge.
At the time, this was an initial idea for heating SVO; it seemed unlikely that the unit would get the fuel warm enough when running continuously, but at £1, it was worth a try. Of course, the heater wasn’t anywhere near powerful enough, and the unit was replaced by the engine coolant/fuel heat exchanger fitted to the bulkhead next to the filter. That heat exchanger for the SVO works very well, but the T-pieces for the coolant lines to the exchanger proved to be a weakness. The unit was disconnected and because of T-piece rupture and subsequent major coolant loss. Furthermore, due to the experience of rapid coking when the Tdi was first installed and run on SVO, I have not had much desire to reactivate the heat exchanger (that may change if the diesel and SVO prices make the mod desirable again – I think I know what caused the coking and how to fix it, so the heat exchanger has remained on the bulkhead). To that end, my fuel has been unheated ever since the trip around the Alps.
The cold snap in December, and having had a cold winter last year, proved good reason to fit the filter heater as orignially intended by Bosch. The unit needs a dedicated supply (it draws 10A), so a relay was fitted to supply power from the auxilliary battery, controlled by the accessory circuits from the ignition switch (green wires) so that the unit is disconnected when the ignition key is removed. This feed then runs through a 15A fuse to the thermostatic switch that screws into one of the blanked inlet ports on the filter housing that switches the unit off when not needed. From there, it goes to the terminals on the sandwich plate that is the heater itself and on to earth. This means that even in the coldest conditions, fuel filter waxing will not be a concern. The unit is automatically controlled by the relay and thermostatic switch, so there are no dash switches or indicators (though it would be easy to rig a warning light in parallel to the heater to show when it’s on).
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