When I removed the fuel tank from my car earlier this, I discovered that it didn't have it's proper in-tank fuel filter fitted to the drain plug. So I started to look into it.
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| Fuel tank filter and fuel tank drain plug |
The in-tank filter consists of a column of thin serrated discs, stacked over a cage-like plastic frame.
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| The discs are stacked over a plastic frame |
The serrations mean that there are very small gaps maintained between the discs. That's how and where the filtering takes place.
The filter unit presses into a recess in the end of the brass fuel tank drain plug.
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| The recess in the fuel tank drain plug |
The other, top, end of the tower has a small hole to the space in the middle of the disc stack. The fuel tank has a curved metal guide tube that the nylon fuel pick up hose fits through. The guide tube ensures that the nylon pick up hose passes down into the middle of the fuel filter stack.
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| The guide tube 'A' steers the pick up hose into the filter 'F'. |
The tank end of the fuel pick up pipe locates within the stack of filter washers via the hole in the tower.
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The filter in the tank. Note the rust! (photo credit: Carter Willey) |
All too often, when the drain plug is removed, the stack of filter washers is found to be clogged and looks like this........
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Clogged filter
(photo credit: Enzo Round) |
It's hard to even recognise it as a stack of separate discs.
Faced with this, some people choose to leave the filter out of the tank and instead use disposable in line filters. The in-tank filters can, however, be dismantled and cleaned to restore their function.
The version of the filter you are most likely to come across consists of bronze discs. Removing the 'lozenge' from the end allows the clipping end of the tower to close up slightly and the washers can be removed more easily. First of all there should be a plastic washer on the end. Next is a rubber 'O' ring.
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Fuel filter
(photo credit unknown) |
It's not uncommon for the 'O' ring to perish or be completely missing.......
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| Perished 'O' ring....... |
Under the 'O' ring are approximately 60 thin bronze discs or washers.
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Filter dismantled.
(photo credit: Colin Smith) |
I can only say 'approximately' as some folk find they have 60 or 61 washers, others find just less than 60.
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| 59 bronze discs and a plastic washer. No 'O' ring..... |
Whatever the number of discs, you don't want excessive gaps between them. That's why the rubber 'O' ring is important - to take up any slack in the stack. If it needs to be replaced, the 'O' ring needs to have an inner diameter of 21mm and have a cross section of about 3mm. Thats assuming you have about 60 bronze discs.
The individual discs can be carefully cleaned. An ultrasonic cleaner is handy for this kind of thing and hanging the washers from a threaded rod means the washers don't gather up. Elbow grease works too.
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| Cleaning the discs in an ultrasonic cleaner |
If properly maintained, the in-tank filter does exactly what it's intended to do.
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| Cleaned filter. Can you see the gaps? |
The filter assembly should clip into the end of the drain plug and stay there - not just sit loose. Though there isn’t really anywhere it can go.
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Plug and filter assembly
(photo credit unknown) |
When refitting the drain plug and washer, it's wise to make sure that the end of the nylon pick up hose extends fully to the bottom of the tank - level with the base.
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Fuel pick up pipe at tank drain hole
(photo credit unknown) |
The drain plug and filter assembly can then be fitted over the fuel pick hose and screwed home. It's also wise to make sure that the end of the pick up hose is cut at an angle. If it's cut square, it may block itself at the bottom of the filter stack.
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| Pick up pipe inside the filter. Note the angled pipe end |
As the filter was missing (or removed) from my car, I got a second hand one from one of the usual parts suppliers. I was surprised to find that, instead of about 60 thin bronze discs, it was made up of 39 slightly thicker serrated plastic discs. The 39 plastic discs equated to the same length/ height as 60 bronze discs.
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| Serrated plastic discs |
Perhaps this version is from the end of DS production or maybe from a contemporary Citroen model? It still works in the same way though.
