Filters and Diesel bleeding
Posted: Tue Oct 07, 2008 9:08 am
We just spent a very pleasant week aboard Q on the Chesapeake. The last day was calm so we drove home with the Yanmar 3GM30YEU chugging away. Got bounced by an a*****e in a powerboat who passed too close. The engine hesitated, then regained rpm. It began to cycle ever more often from the customary 2800 rpm down to 2000 and back up again and it would not rev above 3000 when normally it could turn 3600 or so. I read all the not-so-informative information on troubleshooting and decided that very likely the bounce had stirred up some goop in the tank or filter bowl.
A NE 38's 40 gallon fuel tank is down in the keel; we top up the tank at the end of every season but normally burn only 20-30 gallons a year. We had refilled the tank the day before, 22 gallons. A Racor 500 GFSS is mounted higher than and next to the engine, it feeds the Yanmar's primary fuel pump and filter. Both filters are rated for 2 microns.
I bought a second set of replacement filters, changed out the really gross Racor filter element and the Yanmar's. I filled the Racor with fuel since I could not imagine that manual cycling of the primary fuel pump would draw fuel up from the tank, fill the Racor and then fill the Yanmar's filter (within my lifetime). I found that I could simply fill the Yanmar's filter by opening the filter housing bleedscrew and gravity would do the job. Yanmar's instructions said to open the high-pressure pipes at the pump for each cylinder, but you can't get a wrench on them (they're close together and under coolant hoses); I opened each one in turn at the injectors while Sue bumped the starter. Of course, you can bump a gas engine with the coil wire off and the engine won't run. When you bump a diesel, it wants to run if there's fuel. While bumping, the Yanmar danced and clattered quite remarkably! After opening each cylinder's fuel pipe, seeing fuel, and reclosing, the engine started to run well and continued to do so for the remaining hours home.
Questions: How come the Yanmar's filter was foul when there was a Racor ahead of it? How come the vacuum guage on the Racor read 0 before and after the filter change? How come I could fill the Racor and not simply have that fuel pour down to the fuel tank; do you suppose there's a backflow preventer? There is no access port in the monel fuel tank; how best to 'polish' the fuel and clean the tank?
A NE 38's 40 gallon fuel tank is down in the keel; we top up the tank at the end of every season but normally burn only 20-30 gallons a year. We had refilled the tank the day before, 22 gallons. A Racor 500 GFSS is mounted higher than and next to the engine, it feeds the Yanmar's primary fuel pump and filter. Both filters are rated for 2 microns.
I bought a second set of replacement filters, changed out the really gross Racor filter element and the Yanmar's. I filled the Racor with fuel since I could not imagine that manual cycling of the primary fuel pump would draw fuel up from the tank, fill the Racor and then fill the Yanmar's filter (within my lifetime). I found that I could simply fill the Yanmar's filter by opening the filter housing bleedscrew and gravity would do the job. Yanmar's instructions said to open the high-pressure pipes at the pump for each cylinder, but you can't get a wrench on them (they're close together and under coolant hoses); I opened each one in turn at the injectors while Sue bumped the starter. Of course, you can bump a gas engine with the coil wire off and the engine won't run. When you bump a diesel, it wants to run if there's fuel. While bumping, the Yanmar danced and clattered quite remarkably! After opening each cylinder's fuel pipe, seeing fuel, and reclosing, the engine started to run well and continued to do so for the remaining hours home.
Questions: How come the Yanmar's filter was foul when there was a Racor ahead of it? How come the vacuum guage on the Racor read 0 before and after the filter change? How come I could fill the Racor and not simply have that fuel pour down to the fuel tank; do you suppose there's a backflow preventer? There is no access port in the monel fuel tank; how best to 'polish' the fuel and clean the tank?