Hello everyone, I have a 78 8hp yanmar in my boat and wanted to know if I have to bleed it if I change the first spin on fuel filter and the secondary fuel filter cartridge. Thanks in advance..... Michel cherub78
fuel filters
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Usually Yanmars do not need to be 'bled' for small amounts of air in the fuel system ... air that is NOT in the injection pump - just in the fuel delivery piping and filters.
If you can replace and pre-FILL the filters with oil so that there is a MINIMUM amount of air entrained you 'may' be good to go without bleeding.
1. close the tank valve before changing filters so the line from the tank doesnt drain into opened filter bowl (and into the bilge).
2. Change the filters 'one at a time' starting with the 'lowest' filter in the system.
3. manually fill the filters with oil so that they are fully filled and the filter material/pleats purges its air (bubbles), then close the filter(s). On most Racor housings there is a vent; just pour oil INTO the vent then wait to be sure that all 'bubbles' come back out the vent.
4. Open the tank valve to allow the fuel to 'siphon' from the tank into the filter(s) - the flow of fuel 'should' purge out any remaining air .....
As stated most Yanmars will tolerate a wee bit of air in the fuel system. If you can prevent the lines from draining out by closing the tank valve, can fill the filters with oil before closing them up ... then 'maybe' you can easily restart the engine without bleeding.
'Best way' to do this is to instal a small 12vdc fuel pump somewhere between the tank and the normal engine lift pump ... and simply active the small 12vdc pump to purge the air at the engine mounted 'guard' filter when you need to 'bleed'.
If you can replace and pre-FILL the filters with oil so that there is a MINIMUM amount of air entrained you 'may' be good to go without bleeding.
1. close the tank valve before changing filters so the line from the tank doesnt drain into opened filter bowl (and into the bilge).
2. Change the filters 'one at a time' starting with the 'lowest' filter in the system.
3. manually fill the filters with oil so that they are fully filled and the filter material/pleats purges its air (bubbles), then close the filter(s). On most Racor housings there is a vent; just pour oil INTO the vent then wait to be sure that all 'bubbles' come back out the vent.
4. Open the tank valve to allow the fuel to 'siphon' from the tank into the filter(s) - the flow of fuel 'should' purge out any remaining air .....
As stated most Yanmars will tolerate a wee bit of air in the fuel system. If you can prevent the lines from draining out by closing the tank valve, can fill the filters with oil before closing them up ... then 'maybe' you can easily restart the engine without bleeding.
'Best way' to do this is to instal a small 12vdc fuel pump somewhere between the tank and the normal engine lift pump ... and simply active the small 12vdc pump to purge the air at the engine mounted 'guard' filter when you need to 'bleed'.
I had a Yanmar YSE8 in my Tanzer and always had to crak the banjo valve a few times after filter replacement. Its easy. Takes a 3/4 inch open ended wrench, turn on the switch (to activate the pump) and openthe valve slightly/briefly several times until no more air comes out. Start the engine and crack it one more time. Done.
i found a nice trick that will serve you even if you have to hand crank the motor, put an outboard primer bulb in line right out of the tank, then on yanmars change the filters and do your maintenance, after you are done use the bulb and bleed the on-engine fuel filter, then the injector bypass lines (top bolt on the injector) after bleeding these two stages the motor will start without fault. btw all of these bleed procedures can be done with the motor off throttle closed to idle cutoff and using only the primer bulb, the injector feed line will not bypass air into the return loop of the injection system so once the places i referenced are bled the motor is ready to go.
rufus, WADR, that concept has been suggested many, many times on this and other forums. The response from knowledgeable skippers has been that those bulbs are not suitable for diesel fuel. They suggest that skippers simply install lift pumps, which also make bleeding a lot simpler bit of work.
Our primary filter the Racor usually fills up by gravity and does not need to be bled. The secondary filter attached to the engine is a different story. We just replace the cartridge and crank the engine with the electric starter and it fills the bowl. We open up the bleed screw and crank the engine some more to purge the air. If we close the screw as soon as the engine sputters we spill very little fuel unto a rag we set around under the filter. Be gentle with that bleed screw in the secondary filter as if damaged you will have fuel leaking out and air invading the system.
Benny, what you described as the secondary filter bleed problem with the screw caused me to add the outboard bulb rig as a standby for bleeding. It's not inline all the time; it's installed only when bleeding is needed. This has worked for 10 years without a hitch.
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