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Home \ Sailing \ Technical \ Changing the Fuel Filters on our Yanmar 3GM30F Diesel Engine

Changing the Fuel Filters on our Yanmar 3GM30F Diesel Engine

Another form of preventative maintenance we like to undertake each year is replacing the fuel filters on our Diesel engine. A quick Google search will throw up a variety of answers as too how often one should carry out this task, however the main consensus seems to be between 200 and 300 hours or once a year.

As fuel filters are relatively inexpensive and the process fairly straight forward we deem it an essential part of boat life and change ours at the start of each season. Fuel filters help to remove any bits of debris or contaminants from the fuel system, thus helping the engine to run as smooth as possible.

We have two fuel filters in the system, the first is a Racor R15T Fuel Filter/Water Separator which is a coarser filter and helps to remove water and bigger particles, and the second is a finer filter which is located on the engine itself.

A couple of years ago we replaced our existing Delphi 496 Fuel Filter with the Racor filter from ASAP Supplies. We found the Delphi filter rather awkward to deal with. It used a central bolt, the seals didn’t ‘seat’ easily and it didn’t have a priming pump. The thought of us having to possibly change one of these in a seaway filled us with dread! After much researching we settled on the Racor filter which is a spin on filter and features a self venting bowl and a built in primer in the head.

Below is our step by step guide to how we change these particular two types of filters. Other filters may use different methods and if in doubt please consult your engine manuals or a marine engineer.

How to change the fuel filters?

First up ensure you shut off the fuel feed from the tank.

Place a bowl or jug underneath the filter to catch the excess. Drain the filter by unscrewing the drain valve at the bottom.

Draining fuel filter

Using a strap wrench remove the filter and bowl.

Remove the filter from the bowl and replace the old O ring with a new one, using a little bit of diesel to lubricate.

Screw the new filter onto the bowl, hand tight is sufficient, and screw back onto the filter housing. Use the strap wrench to nip it up.

Racor R15T fuel filter / water separator

Follow the fuel line along and you should come to the secondary filter. Ours looks like the following with a ‘castellated nut’ on top.

Secondary fuel filter

Undo the nut – you may need to use a small bit of wood or similar slotted into one of the ridges, gently tapping it with a hammer to loosen it enough to unscrew by hand. Carefully remove the bowl – there will be fuel in here so handle with care to avoid any spillages! You will now be able to see the filter.

Secondary fuel filter

Pull down to remove the filter. Here is our ‘old’ one – as you can see it still looks pretty good to us and would probably continue to last for a long time but as we were changing all aspects on the engine we replaced anyway.

Used filter from our Yanmar Diesel engine

Replace the filter, check the O ring and replace if necessary. Screw the housing back into situ and nip up the castellated nut.

As we have opened the filters we will have introduced air into the system. This must be bled before the engine will run. We have two bleed screws on our engine. The first is located just above the secondary filter. Gently loosen this about a quarter of a turn using a spanner.

Bleed screw above fuel filter

The benefit of our Racor filter is that it has the built in primer in the head. Pump this to begin priming the system.

Primer on Racor fuel filter

As you pump you will soon start to notice air bubbles coming out of the bleed screw.

Air bubbles coming out of bleed screw

Continue pumping until all the air has been expelled and clean fuel starts to seep out of the bleed screw.

Fuel seeping out of bleed screw

Once you are satisfied that you have only fuel coming out, tighten the screw back up and move onto the second bleed screw which is located on the injector pump.

Bleed screw on injector pump

Again follow the same procedure as with the first bleed screw. Loosen it slightly, continue pumping until all air bubbles disappear and fuel starts to seep out. Nip the screw back up when you’re done.

Hopefully you will now have removed all air from the system. Re-open the fuel shut off valves and give the engine a run. Carefully check all areas for any leaks. If you do notice any then you will need to shut down, investigate the problem area and possibly re-bleed the system.

We like to give the engine a good hour run just to ensure all is well. Engines aren’t keen on running cold, they like to run hot. Running an engine for a short period of time can cause excessive wear. We normally run at idle for 5-10 minutes then engage forward gear to put the engine under load, running at around 1100rpm for at least half an hour, but ideally an hour.

On a similar fuel related note we started using Marine 16 Diesel Fuel Complete last year which helps to prevent the growth of diesel bug. Check out this post to see how we’re getting on with it!


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