Pug 306 diesel, fuel temp regulator

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Fri 29 Jul 2005 10:47
Pug 306 diesel, fuel temp regulator - solara
Hi,
I recently had to replace one of the leaking o-rings on the fuel regulator in the fuel filter housing. This has now got me thinking about how it works and what its purpose is, and a possible modification.

For those with a 306 diesel, it can be seen on the bottom left corner of the fuel filter housing where the fuel inlet pipe comes in. It looks like a white drain plug with a crossed head.

The fuel regulator is definitely thermostatically (temperature) controlled, and opens/closes a valve to the fuel heater circuit. The fuel heater circuit is below the plastic filter housing (seperated by a large o-ring) and is cast into the base of the metal coolant heated base. Those with a haynes manual can see a pretty good picture of this in the diesel fuel/coolant section. The pattern of flow can be seen running between 11 o'clock and 1 o'clock (if it were the face of a clock), in a spiral pattern to maximise the heat transfer form the coolant circuit to the fuel flow circuit.

My guess is that the fuel regulator when cold, shuts off the flow to the fuel heater circuit. As the coolant temperature rises, it opens the fuel heater circuit gradually mixing the colder fuel with the hot fuel (rather like a mixer tap).

My theory behind this is that, on frosty mornings, the cold metal fuel heater circuit is more likely to gel the diesel than inside the warmer plastic filter housing.

Is my thinking right? Anyone else have a better idea or knowledge of how it actually functions? Does anybody know the direction of fuel flow in the heater circuit (eg 11 oclock to 1 o clock or vice-a-versa). Any idea of what temperature it regulates the fuel at? I guess I could measure the temperature from the fuel drain pipe when hot.

The reason I ask is that this 306 is turning veggy (running on veg oil), and veg oil ideally needs to be heated to 85 deg celsius to be at the same viscosity as diesel. I am also considering the option of adding an extra glow plug to the metal fuel heater circuit, to help melt the thick veg oil on cold starts.

Thanks
solara
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Fri 29 Jul 2005 12:01
Pug 306 diesel, fuel temp regulator - RichardW
Don't know about the fuel temp, but make sure your car has a Bosch pump before comitting to Veggie oil - it can destroy the Lucas pump pretty quickly. Bosch pump easy to identify - the cold start cable goes to the back of the pump, and the boost compensator is a big lump sticking out of the top.
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RichardW

Is it illogical? It must be Citroen....
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Fri 29 Jul 2005 12:39
Pug 306 diesel, fuel temp regulator - solara
Yes I made sure its a Bosch pump. Been running on 80%veg/20% diesel for a month now. Engine is much quieter and smoother. Even the wife mentioned it!
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