Sunday, 1 June 2014

Changing diesel filter gets off to bad start

In theory I knew what to do. In practice I fell at the first hurdle. OK, the second one. Turning off the fuel tank stop tap didn't give me any problem.

diesel filter before work started

close-up of drain screw

It was the unscrewing of the drain tap under the diesel filter which didn't go according to plan. It was, as I have mentioned before, a plastic bung which didn't want to turn. So I used a bit more force, and tried rocking it backwards and forwards. Eventually it seemed to become a little freer, so I unscrewed - and it came off in my hand. The end did.

The actual bung bit, which stops the diesel/water/sediment falling out remained firmly in situ.

At this stage I could have given up. I was reasonably confident that the filter wouldn't leak - it felt dry underneath. But having got all the tools to hand I thought I'd remove the filter anyway, and see if I could remove the drain screw when I could see it a little better. So I unscrewed the centre bolt, and the bottom part of the filter unit split easily from the rest. Jan took a photo as I carefully caught nearly all of the fuel in a plastic milk "bottle".

Next I jiggled the middle section, the actual filter, until it, too, came away. Is that jelly-like gunge on top the dreaded diesel bug?

Having wiped off the gunge I then tried to get the filter out of its container. It did not want to budge. Eventually I realised that the whole of what I was handling was the replaceable element. Well, I didn't know!

This was as much as I could do before sorting out the drain plug, so I cleaned up and took a photo of the underneath of the filter head. Ah - so that's where another of the supplied O-rings goes!

Here's a question. If what I have been working on is the fuel filter, on the right in the photo below, then what's the red thing on the left which also looks like a filter? The output of the first filter goes directly to this.

Here's a clearer photo of the red device.

It actually has the word "filter" on it. Just done a search: it is indeed a fuel filter. I suppose I ought to replace this one too.

I have now left the boat with the fuel tap turned off, and with the filter head exposed. How long do you think I can leave it in this state? Our next stint of boating isn't due for another six weeks - is this too long to leave it?

We drove home today to lawns of daisies and dandelions. I shall have to get the mower out, but I shall also have to have a go at the filter bowl.


Davidss said...

Yes they are both filters. Yes, as you appear to be uncertain of the service history, change both. It may have been that previously only the red filter has been changed as it's a simple 'unscrew the old, screw on the new'. Taking this further, the gunge in the old filter may have built up over a long period of time; you won't get a true picture until the next service interval. If the engine was running before you started the service then fuel was still flowing, so I don't think any immediate remedial work is required. As you have discovered, you have two filters, so the pump and injectors are 'double protected'.
The advantage of the old filter housing is that the lower section, with the drain plug, is a water and sediment trap. If you ever think you have taken on water contaminated fuel, or left the tank substantially empty over a long period (when condensation can build up), then opening the drain tap allows you to drain the water away.
Yes, I'd say you can leave the fuel system open for 6 weeks, as you describe. Your biggest concern will be spiders and bugs using the holes as homes, but I suspect the excessively oily ambiance will keep them away. 'Next time' you may feel happier wrapping any open units in cling film.

I suggest asking around at your 'local' diesel specialists, or on a Forum. Yours won't be the first plastic drain plug to have sheared; there may be brass or bronze alternatives available. Whichever, grease the threads before reassembly, even if you use a plastic one, and don't over-tighten.


kevin t said...

Hi Halfie,
What you have removed is the primary filter or agglomerator. It removes water and larger particles from the fuel and, as can be seen in your photo also collects diesel bug. This is a problem for the filter as it will block up very easily and in extreme situations cause the engine to stop. I understand you ran out of fuel the other day, and this is a contributory factor to what can be seen now. When fresh fuel was dispensed into the tank it disturbed the sediment which then found its way into the filter. Fitting a new filter may not solve the problem, but a dose of one of the proprietary diesel bug products might help depending on how infested the tank is. Ultimately, the fuel needs polishing and there are many places now offering this service. Be sure to have the tank and fuel lines cleaned at the same time.
The broken plastic fuel drain clearly needs replacing and I would seek a brass or stainless replacement.
The secondary or fine filter (red in your case) is designed to stop the finest particles reaching the critical parts of the injector system. This should be replaced at the same time as the primary filter unless it was replaced recently and is still fairly new. It does not stop water getting through so if the primary filter does, for whatever reason, allow some water to pass, then this will for sure reach the injectors where if left will cause corrosion and failure of the injector.
It should be OK to leave it for a short while without a filter and with the fuel cock turned off, but I would want to get it sorted ASAP.

N. B. Tranquility

Halfie said...

Davidss, good point about the ease of replacing the spin-on filter compared with the other one.

Kevin, yes, I'm thinking I might return to the boat sooner rather than later to finish the job and make it all fuel tight again.

Thanks to both of you for your suggestions.