Fuel System Overhaul

by Adrian on January 31, 2013

I’ve sailed enough miles to know that fuel and engine problems can seriously disrupt your day – whether it’s sailing into a marina with no working engine or struggling with an engine that won’t provide any power.

New fuel systemFor this reason, I’ve just completed a major overhaul of our fuel system, replacing the standard single filter with dual Racor filters, a supplementary electric priming pump and fuel polishing system.

The filters
The Racor 500FG Duplex is the king of small boat filters. It has two filtration units connected with a multi directional valve so each can be used independently or together.

It is dual purpose, providing both filtration and water separation. Each filter has a glass bowl so you can clearly see the separated water and easily drain it off.

Racor 500The filter cartridges are cheap, standard and easily changeable. It has a spin-on design, which means you simply unscrew the top T handle, remove the cap and pull out and replace the element. There is no mess, no tools are required, and the fuel system does not need bleeding afterwards.

The recommended primary filter for yacht engines is 10 microns, but I also bought a few 30 micron filters for fuel polishing and a tough re-cleanable cartridge as a last resort. The integrated pressure gauge shows the vacuum pressure the fuel pump is exerting, which visibly indicates the filter state and efficiency (the more clogged up the filter is, the harder it is for the fuel pump to suck fuel through the system).

The real benefit from this dual filter system is that one clogged or contaminated filter can be changed whilst the engine is running on the other one.

This gives backup and system redundancy, which is one of my boating maxims.

Diesel bug
With the ever present threat of contaminated fuel and diesel bug, I installed a diesel bug separator unit after the Racor filters. DebugL140.jpegThis simply passes filtered fuel through a vortex of static magnets, which apparently swirls and centrifugally rips apart any microscopic diesel bug organisms still in the fuel.

Agriemech Diesel bug protection This may sound far-fetched but the theory makes sense and it is a fit and forget part – so can’t do any harm. I bought the New Zealand produced De-bug L140 unit from the UK based company Agriemech as it seemed the best designed and most competitively priced unit. It needs no maintenance or cleaning and just sits in the vacuum side of the fuel line doing its job. Installation Instructions

A major reason for the recent increase in fuel problems is because the EU have recently introduced a new directive which requires diesel to be produced with massively reduced levels of sulphur. The easiest substitute for sulphur is Bio-diesel FAME (fatty acid methyl esters) which are added to the mineral diesel. It would appear that micro-organisms such as diesel bug love FAME.

During periods of storage when fuel is not being agitated, the FAME attracts moisture which allows organisms to grow – commonly known as diesel bug. Any condensation forming in the tanks sinks to the bottom and provides a ripe breeding ground for diesel bug proliferation. Ultimately this becomes a thick black sludge sitting in the bottom of tanks, just waiting for a (in)convenient time to be sucked up into the fuel system – usually in a heavy sea when the tank’s contents get mixed around.

Since risk of diesel bug is a fact of life nowadays, installing a diesel bug separator just makes sense and is another good precaution.

Fuel priming pump
Another fuel system upgrade I’ve added is an electric priming pump plumbed into the fuel line between the engine and the filters.

Facet Fuel PumpThis sucks fuel from the tank, forces it through the filters and onwards towards the engine. Air can be then bled out without having use the engine’s manual pump.

I also added an additional bleed valve after the priming pump, so air can be removed and the flow of fuel out of the filters verified.

Another reason to revamp the whole system was the inclusion of a diverter valve which can send filtered fuel back to the tanks instead of to the engine.

Fuel polishing
This allows fuel to be flushed through the filters, through the diesel de-bug unit and straight back into the tank. Known as fuel polishing, and is an operation that can be performed to clean all the fuel in the tanks if it becomes contaminated – without running or risking using the engine.

Extra fuel pump
This pump can also be used as an additional priming pump to force pressurised fuel along the fuel lines into the engine. This can provide supplemental fuel pressure in case the engine’s fuel pump dies, loses efficiency or a pipe blockage restricts normal fuel flow.

Generator fuel
The boat’s original single filter has been redeployed as a completely independent filter/strainer for the generator’s fuel. I have also installed a cross-over pipe and valves to allow the output of the generator filter to feed the engine and vice versa if necessary in an emergency. To complete the job I replaced the single fuel feed line from the primary tank with dual lines and dual pickups, ran fuel lines into the technical cabin ready for the generator (coming next) and repositioned the raw water strainers to the other side of the engine bay for easier access.

Fuel System Schematic

Installation was reasonably straight-forward once I’d planned the layout, pipe positioning and organised and ordered all the bits.

Pipework construction

Fuel System

It was time consuming neatly mounting the new filters, pipework, pump and electrics neatly on the engine bay bulkhead, but worth taking the time to do a good job that was sympathetic to the engine layout and improved instead of restricted access.

The costs were approximately:

£650 Twin filter Racor 500
£100 Diesel de-bug L150 filter
£40 Auxiliary electric priming pump
£300 Stainless steel valves, connectors, hosetails, angle pieces etc.
£50 Replacement and additional 3/8″ fuel hose
£15 Heat resistant aluminium engine bay lining tape
£150 Spare filters (15) to last a few years
£10 Heldite jointing compound
£10 Fuel pump switch, fuse, cable and crimp connectors

…and about 10 hours preparing, installing,, re-running fuel pipes and testing everything.

It is interesting to note that most quality marine and plumbing parts cannot be sourced locally around Brighton, so were purchased online via Asap Supplies Ltd and other ebay based plumbing specialists. Once I had a good understanding of fuel pipe dimensions, 3/8th and 1/2″ connections it was all pretty straight-forward.

Heldite jointing compoundFinally, I would recommend the Heldite jointing compound to ensure air/fuel tight seals between metal threaded components – especially when items need to be screwed together to align, so can’t be screwed completely to the end of the thread.

{ 4 comments… read them below or add one }

Geoff Rogers November 19, 2016 at 17:07

I have a Najad 400 with a single filter system and looking at the dual Racor approach. Your design although complex provides lots of options – I also have twin tanks and a generator. Would you do anything differently reflecting on your experience since installation? Thanks Geoff Rogers


JB October 17, 2013 at 19:11

Great website guys. Please keep it up. Curious that you’ve installed the magnetic D-Bug unit after the Racors while the information appears to say it should be placed between the tank and the Racors. Wonder if the vacuum gauge had a role in this. Would the readings be falsely high if device place before the Racors. In any case, very interested to hear your conclusions about this device as we lost the engine last week while entering the marina channel due to a very dirty fuel tank. Thanks in advance!


Bill Petrie September 14, 2013 at 05:19

Just curious why the two Racor bowls seem to have different colour diesel. Nice practical article. Thanks.


Adrian September 14, 2013 at 06:34

One is red diesel and the other is normal diesel. I have red diesel in the tank from uk sailing (where Yacht owners can buy reduced tax commercial diesel that is dyed red) and initially topped up the filters with normal ‘white’ diesel (from St Petersburg, Russia interestingly at $0.50c per litre!).

I haven’t needed to switch filters yet.


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