Filter modification for Peugeot and Citroen

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There is a hidden heat exchanger under the Peugeot fuel filter. This page details how to modify the filter housing to permanently heat the fuel using the heat exchanger. The heat exchanger uses engine coolant, typically 70-80°C, which is fully passed on to the fuel. There are also many points where air can leak in, and fixes for these are also detailed.

Applicable vehicles

  • Peugeot
    • 205
    • 306
    • 405
    • 406
  • Older Citreons
  • Some Fiat Ducato vans


Note that the OEM system initially heats the fuel with the coolant, then when hot a stat bypasses the heat exchanger and delivers fuel straight to the filter.

Rotary-Motion has come up with a mod called the one pence "penny trick" - this blocks the fuel going to the filter and makes it all go down through the heat exchanger first, heating the oil constantly.

Heat exchanger
Mating face of the filter/stat housing
Water sensor
The parts that make up the stat control, which are to be removed.
This is the bleed off valve for water in the fuel. There were issues with this sealing, fixed by adding an extra o-ring.
By cutting the innards of the stat short and adding a penny into the hole to block off the fuel path directly to the filter, all the fuel has to pass through the heat exchanger first. This was also silicon sealed in, as the o-ring alone is inadequate.
The top of the stat, also silicon sealed in place
Water sensor silicon sealed in
This is where the oil goes down and through the heat exchanger
Both filter base (and heat exchanger surface) were sanded before refitting with original o-ring and more silicon sealant to provide an air-tight seal when refitted.

Summary of changes

Diagram showing fuel flow change

Images and guide content courtesy of Rotary-Motion

Rotary-Motion 22:02, 7 December 2010 (UTC)