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How to change the fuel filter on a Mazda Bongo 2.5 diesel engine

The fuel filter is a cartridge filter, similar to an oil filter, and it’s bolted to a chassis member under the driver’s seat.

Before the filter is removed, it’s necessary to disconnect and then unscrew the white plastic sediment trap from the bottom of the filter body. It has a cable attached to it and to avoid twisting the cable this should first be disconnected at its plug - follow the lead from the bottom of the trap to a junction socket on the chassis member just to the rear:

Access to the fuel filter is easier if the airfilter and associated plastic ducting is removed. Even then, it’s difficult to get at the filter to unscrew it. I found it easier to remove the filter bracket by unscrewing two nuts holding it to the chassis member bracket. This allows it to be turned on its side to put a chain wrench around the body. Locate the filter bracket back on the two studs to allow unscrewing.

The filter’s full of diesel fuel so you need to catch this as you unscrew the trap. (There’s a plastic nozzle on the bottom of the sediment trap and if you attach a tube to this you can drain the fuel into a container as you unscrew the trap.)

Re-assembly with a new filter is the reverse of disassembly, except it’s easier to screw the sediment trap back onto the base of the new filter before fitting the filter to it’s housing. It helps to smear the rubber gasket of the new filter with a bit of clean diesel oil before screwing it back till it hits the housing, then further screwing it by hand (not wrench) another half to three quarters of a turn to tighten.

There’s also a fuel line ‘banjo’ joint with its own small mesh filter that’s worth cleaning with petrol while you’re at it. Below is the banjo bolt and the tiny mesh filter is shown with a bit of bent wire used to carefully extract it. Be careful as there’s a spring in there too.

The bent wire removal option needs care to avoid damaging the filter. I’ve read others have managed to remove the filter using a ‘baby bud’ - cotton tipped probe.


Banjo joint

Fuel filter