Increased fuel consumption after fuel filter leak

[Keith_S]

Hi,

I recently posted on here asking for help following a fuel filter leak. The cause being a damaged / degraded seal on the fuel filter drain plug.

I ordered a new fuel filter housing with a view to using the plug only or, if that wasn't possible, replacing the old housing with the new. The plug on the new filter housing was such that you couldn't remove it without destroying the rubber seal.

So I replaced the housing but when using the o-ring from the old housing it was clear that the o-ring did not sit snugly in its groove / channel in the new housing, it was slightly too large, or at least that's how it looked. The new housing was a cheaper part and I wonder whether it wasn't an exact match. Anyway, started the engine and there was a leak from where the filter housing screws in. I took it off, put the old housing back on, using the old o-ring and re-instating the temporary repair I had previously done (a hose with 2 hose clips - see attached photo.) No leak, or so I thought.

I did my first long drive yesterday however and fuel consumption seemed substantially up: 148km on just less than a quarter of a tank. It seems clear there is something wrong. I have no idea what it might be. As you can see from the photo I attached a cut down bottle to try and catch any leak, I thought maybe it only happens when I'm driving. There was nothing in this.

I should say that there is a very small drip / weep from where the hose attaches to the point where the drain plug should. But I BELIEVE this is tiny (and the bottle contraption didn't catch / show anything). So any suggestions for the increased fuel consumption? Could there be air in the system (I didn't bleed it), but I have no idea if this would do anything to fuel consumption anyway?

I think the only way forward for me is to order another, higher quality, fuel filter housing or the drain plug by itself. I can see that this https://tpuk.net/fuel-filter-air-valve- ... 81617.html for example could be screwed in and the seal added from above (or at least that's how I assume it would work).

One question on the o-ring, is this okay to re-use? I know it's not best practice but the fuel filter was recently changed so it is new.

Any help really really appreciated here - I am in a difficult situation: in France by myself living in my van and I need to be able to drive with confidence, not fearing that I'm making the situation worse or leaving a trail of fuel anywhere.

[dumper]

I’d get a genuine compleat one from Ford I’ve never used transit parts uk but they’re are posts on hear with bad feedback mate had some parts from them and said he wouldn’t use them again

[Keith_S]

Ford parts seem massively over-priced and an exercise in making money. For example £35 for an o-ring: https://shop.ford.co.uk/products/transi ... ing-o-ring

I have ordered a Vaico fuel filter housing, it comes with the o-ring.

I have done some more looking into the situation regarding high fuel consumption and the Google AI insists that it this because of air ingress due to the imperfect nature of the seal I have created. Clearly it is imperfect as there is a tiny leak.

The information also made clear that damage is being done to the fuel pump and fuel injectors because of the presence of increased air.

This makes me really concerned, I am trying my best to take good care of the vehicle, invest in maintenance and so on. Since doing the temporary repair I have driven 180km. I'd be grateful for some reassurance / guidance around this, will damage have been done? Should I absolutely not drive unless essential (I may have to drive to pick up the part from where it is being delivered to)?

For context, I am in France by myself, living in my van hence not really being able to get support elsewhere so any help or advice is really appreciated.

[dumper]

With you mentioning the price of the O ring sounds like you are only buying the bowl I would if mine id get the complete unit with the filter in it

[Keith_S]

The filter was replaced recently (local garage in the UK). And I can't help but think that may have been the start of this whole scenario / shambles. And I can't help but be annoyed that even if it didn't cause the problem, the drain plug seal should have been inspected given age of the vehicle. Or am I expecting too much?

As part of trying to fix the problem I removed the fuel filter housing and sitting by itself at the bottom of it was a rubber ring which I assume had previously been attached to the drain plug and formed the seal (when it was working).

It is very hard for me to get parts where I am but the filter itself might be easier to get. How important do you think it is to replace the filter too?

[dumper]

As I said for me personally I’d change the complete unit and that would be with the element as well the O ring you mentioned is probably off the centre of the filter element to seal it to stop it being bypassed
As mine is still under warranty I’ve not had to change it and the previous van was changed when it had problems on holiday in Ireland when out went into limp mode so I’ve not changed them myself so not 100% sure on the O ring but likely to be from inside

[metalworker0]

Did a re-gen happen during your latest fuel mpg / kpl test .. if so, according to google, it will burn away between 1 and 2.3 liters

all the best.mark

[Keith_S]

Thanks for those replies. A few things have come up since then:

1. Did some more research into this and my understanding is that air ingress at the temporary repair would not cause the type of problem identified by AI. This is because that part of the fuel system isn't under pressure; from a commonsense perspective at the very least I find it impossible to believe that a little rubber seal on the fuel filter drain plug would be given the responsibility of protecting the fuel system.

2. I drove 4km yesterday as I had to move where I was parked, when driving the fuel gauge needle unexpectedly went back to where I would expect it to be for the distance driven. Perhaps therefore it's all in my head...

I'm not aware of a re-gen having taken place, I'm not even sure what that is either, is it to do with the DPF?

I am still interested to hear whether air ingress (from what is equivalent to a degraded seal on the fuel filter drain plug) could cause damage to the fuel system?

[dumper]

A regen is when the DPF cleans itself as for going on the fuel gauge movement it will change at times by the angle you park at if not level and using level blocks the best way to check fuel consumption is fill it to maximum run it till required a refill and work it out by mileage and fuel on refill and if possible use the same fuel pump so van is set at the same level

[metalworker0]

Yes regen is the regeneration of the DPF.. it squirts diesel into it .. which burns the soot away .. .. should happen once every full tank of fuel.
Your gauge playing up .. could be a sign that its about to fail. or something to do with the level sensor in the tank sticking.
Im not a diesel mechanic .. but air in fuel can cause problems .. the pump is lubricated by diesel going through it .. which isn't a good lubricator in my opinion .. so air bubbles could make it worse

.. but i would have thought that air would also make its way to the injectors and the engine would run rough

What google AI says

Yes, air in a diesel fuel system can cause serious damage and operational failure.Diesel fuel systems rely on dense, liquid fuel to lubricate and cushion high-precision components operating under extreme pressures (often from 10,000 to 30,000 PSI). When air mixes with the fuel, it creates several damaging effects:
Loss of Lubrication: Diesel fuel acts as a lubricant for moving parts inside the fuel injectors and pump. Air bubbles break this vital lubricating film, leading to metal-on-metal friction, galling, and scoring of components.
Cavitation Damage: As air bubbles travel into high-pressure zones and collapse, they create a violent micro-explosion effect called cavitation. This process tears microscopic chunks of metal away from pump and injector surfaces.
Mechanical Shock: Because air is compressible and liquid fuel is not, air pockets act like a weak shock absorber. This increases the mechanical force on injector plungers by up to 50%, which can crack or break injector tips
.Erosion (Cutting Torch Effect): High-pressure fuel mixed with air rushing through tiny injector nozzle orifices creates a blowtorch-like effect. This erodes and enlarges the nozzle holes over time, ruining the spray pattern.
Performance Issues and Airlock: Air does not build the necessary hydraulic pressure to trigger timely fuel injection, leading to delayed timing, rough idling, misfires, loss of power, hard starting, or a total "airlock" where the engine fails to run.

all the best.mark

[metalworker0]

Just to add .. air in the fuel is probably unlikely when running ..as it has a pump in the tank (other earlier transits did not have a pump .. they are more likely).. so i think it's under pressure .. the air is only likely to be there when its stopped and leaked in as fuel drips out. or if the pick up in the tank has fallen off.

all the best.mark