Keep it clean

Diesel sys­tems need to be checked and have new fil­ters fit­ted reg­u­larly, es­pe­cially with fuel bug is­sues. Here’s how

Canal Boat - - Technical -

When it comes to ser­vic­ing the fuel sys­tem most peo­ple think of the diesel me­chan­i­cal parts, but just as it takes two to tango it takes two for an en­gine to work prop­erly – fuel and air.

Blocked air fil­ters or other forms of air re­stric­tion stran­gle en­gines and pro­duce black smoke, so if your ex­haust is smok­ing and you find your fil­ter is badly clogged, sim­ply take it out and run with­out one un­til you can ei­ther clean it or get a re­place­ment.

‘Pan­cake’ or ‘fry­ing pan’ fil­ters are the sim­plest to deal with, they just need the old ‘pa­per’ el­e­ment re­mov­ing and re­plac­ing. There’s usu­ally ei­ther a cen­tral wing nut or clips around the cover hold­ing the parts to­gether.

Mesh fil­ters re­quire a lit­tle more work, their wire or plas­tic foam needs to be re­moved and washed out in white spirit or paraf­fin, dried and then coated with a thin film of en­gine oil to trap the dust. Don’t be tempted to re­new a foam fil­ter by cut­ting up odd pieces of foam you hap­pen to have ly­ing around, they must be made from open cell foam that al­lows air to pass through.

Not all en­gines have air clean­ers. Some Ve­tus en­gines look as if they have one, but it’s ac­tu­ally only a si­lencer to qui­eten the noise of the air in­take. Some older Perkins and Lis­ters sim­ply had a sort of metal ‘dome’ to stop you drop­ping things into the air in­take and some Isuzus might not even have that.

If there’s a hose run­ning from the top or side of the en­gine into the air cleaner, or a point very close to it, take the hose off and ei­ther clean it out or re­place it. Also make sure any metal con­nect­ing pipes are clear.

Mov­ing on to the diesel as­pect, first, switch off the fuel tap (it’s easy to for­get…) and place a bilge blan­ket un­der the wa­ter sep­a­ra­tor (if you have one) and fil­ters.

A wa­ter sep­a­ra­tor is usu­ally the first ‘fil­ter’ in the fuel line from the tank, so re­move the bolt hold­ing the bowl on and try to catch any diesel that runs out in a tub or bucket.

Pour the re­main­ing con­tents into the tub and in­spect it for signs of wa­ter (glob­ules mov­ing across the bot­tom), cloudi­ness any slimy grease/jelly like sub­stance. The lat­ter two in­di­cate that fuel bug may be present, even if you are not suf­fer­ing any prob­lems. Gritty par­ti­cles are rust or dirt and show that the unit is do­ing its job.

Wash the com­po­nents in clean paraf­fin or white spirit and dry them with a lint-free cloth, then re­assem­ble, re­new­ing any rub­ber seals as nec­es­sary.

If the fuel pump has a fil­ter or strainer move the tub and blan­ket be­neath the pump and clean them, oth­er­wise place it below the en­gine fuel fil­ter(s).

On a mod­ern en­gine th­ese are likely to be ‘spin-on’ types, but older en­gines might have a pa­per el­e­ment in­side a bowl or a metal/pa­per el­e­ment sand­wiched be­tween the fil­ter head and a shal­low bowl. Both are dealt with in the same way ex­cept that the ‘sand­wich’ type has rub­ber seals above and below the el­e­ment, while the bowl type only has one seal in the fil­ter head. The bowls of the lat­ter two are re­tained by a cen­tre bolt at the top or, oc­ca­sion­ally, at the bot­tom of the assem­bly.

When you’ve re­moved the fil­ter, empty fuel from it into the tub and in­spect the fil­ter and tub for signs of diesel bug or wa­ter. Fill the new fil­ter with clean fuel

and screw it on un­til it touches the head and then another half to three-quar­ters of a turn by hand.

If your en­gine has a me­chan­i­cal fuel pump re­move any screw(s) hold­ing the cover onto it and re­move the cap, en­sur­ing you don’t dam­age a rub­ber seal­ing ring. Re­move the strainer and clean. If there is a sed­i­ment trap below the strainer clean it with lint-free cloth and (prob­a­bly) a small screw­driver. Check for signs of diesel bug or wa­ter.

Some Mit­subishi-based en­gines (and pos­si­bly oth­ers) use an elec­tric fuel pump with a small fil­ter in one end. It’s vi­tal that this fil­ter is changed reg­u­larly – es­pe­cially if there is no wa­ter trap. This is done by un­screw­ing the ‘bay­o­net’ end cap and re­mov­ing the small el­e­ment. There is also a mag­net un­der the cover that re­quires clean­ing. Check the fil­ter and hous­ing for signs of wa­ter or diesel bug.

Once it’s re­assem­bled, if your sys­tem is said to be self-bleed­ing and your bat­tery is in good con­di­tion, turn the fuel tap on and op­er­ate the starter in 30 sec­ond bursts. Even­tu­ally the en­gine should fire and run – pro­vid­ing the bat­tery holds out.

If not and you are lucky, you will only have to bleed the low-pres­sure side of the sys­tem. How­ever oc­ca­sion­ally you may then have to go on to bleed the high­pres­sure sys­tem and you cer­tainly will if you run out of fuel for any rea­son.

First check the man­ual and read what is it says about bleed­ing the fuel sys­tem. If the boat has an elec­tric fuel pump and a small pipe lead­ing from the fil­ter or in­jec­tor pump back to the tank, you are in luck. Just turn on the fuel tap and ig­ni­tion and the elec­tric pump will drive the air back into the tank.

For man­ual bleed­ing, it might be pos­si­ble to bleed any wa­ter traps by grav­ity, oth­er­wise you will have to pump the air out of the sys­tem via the fil­ter bleed point.

To bleed the wa­ter trap by grav­ity, loosen the bleed point on the trap, if it has one, or the out­let pipe union. Spit around the loos­ened point and watch for bub­bles of air com­ing out. Once no air is com­ing out, tighten pipe and move on to bleed­ing the fil­ter(s). When fuel leaks from the bleed point or union, tighten it and clean any spillage.

To bleed the fil­ters, loosen the bleed point on the fil­ter head and op­er­ate the prim­ing pump. First air should come out of the bleed point, then bub­bles, then fuel in­ter­spersed with air and fi­nally just fuel. Then tighten the bleed point.

If you can­not get pure fuel to flow you prob­a­bly have a faulty seal or soft washer on the wa­ter trap or lift pump cover.

Mod­ern en­gines usu­ally have a self-bleed­ing in­jec­tor pump, but they can still be bled from the point where the pipe that re­turns to the tank is fit­ted to the in­jec­tor pump. Bleed­ing it if nec­es­sary is much the same as the fuel fil­ter.

If you need to bleed the high pres­sure sys­tem to get the en­gine run­ning, loosen the in­jec­tor pipe nuts at the in­jec­tor end, half a turn is ad­e­quate, spin the en­gine on the starter and watch the pipe unions. When they us­tart to spit or drip fuel tighten them. The en­gine should now start.

Bleed­ing the fuel has prob­a­bly the largest po­ten­tial for prob­lems, so if you are at all un­sure get some­one to show you how to do it (even if the man­ual says it’s self-bleed­ing).

Change pa­per air cleaner el­e­ment

Gauze-style air cleaner

Check wa­ter traps

Prim­ing arm on fuel lift pump

Change the fuel fil­ter

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