Filters and Diesel bleeding

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Quetzalsailor
Master of the Arcane
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Joined: Fri Aug 26, 2005 9:53 am
Boat Name: Quetzal
Boat Type: LeComte North East 38
Location: Philadelphia, PA

Filters and Diesel bleeding

Post by Quetzalsailor »

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?
David

Post by David »

<<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!>>
If you open the compression release levers the engine will not start and you can crank the starter all you want.

Questions: How come the Yanmar's filter was foul when there was a Racor ahead of it?
A: I suppose what you saw in the Yanmar filter was smaller than 2 microns.

How come the vacuum guage on the Racor read 0 before and after the filter change?
A: It's not working? The Racor was not restricted enough to register on the vacuum guage? Perhaps you got air in the line from the "bounce" not crude--the engine might hunt around in the same way. I personally think that much lift from your keel tank may be too much for the small Yanmar lift pump. Have you considered adding an electric fuel pump to help? It would also make bleeding much easier.

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?
A: The feed side of your Racor will prevent backflows. Keep in mind there are two basic designs of Racors: pull filters and push filters. Be sure you have the right type.

There is no access port in the monel fuel tank; how best to 'polish' the fuel and clean the tank?
A: Can you push a small flexible hose down the fill pipe? Perhaps you can use it to suck some of the muck up. You could set up a rig using an electric fuel pump to pull fuel from the tank, thru a fine filter and back to the tank via the diesel return line. I'm not sure how effective that would be to "polish" the fuel.

Good luck,

David
Quetzalsailor
Master of the Arcane
Posts: 1100
Joined: Fri Aug 26, 2005 9:53 am
Boat Name: Quetzal
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Post by Quetzalsailor »

Oh! Good reminder about the compression levers!

Both filters are 2 micron and I have not seen any for smaller. The replacement filters for the Racor are available in 30, 10, and 2 microns and are color coded for the size.

I kinda' wondered about that lift and the teensy Yanmar primary pump. Seems to have worked for 1600 hours, though.

The Racor 500 is rated for installation either ahead or downstream of the pump but is restricted to 15psi on the pressure side. The guage reads either vacuum or pressure (like the vacuum-pressure guage in a supercharged Studebaker).

I'll call around for folks in my part of the Bay who do onsite polishing. Most of the little literature I read calls for scrubbing out the tank. Certainly the stuff I encountered in the settlement bowl of the Racor and around the filter of the Yanmar was pretty stiff, dense paste!
Jason K
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Post by Jason K »

You may want to consider using a 10 micron filter in the Racor and relying on the 2 micron motor-mounted filter for the finer particles.
- Jason King (formerly #218)
J/30 Rambunctious
http://www.rambunctiousracing.com
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