Air in Fuel Line #sabre34MkII


David Wall
 

I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


chassidwa
 

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


Allison Lehman
 

I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David



chassidwa
 

Do all injector pumps have built in filters? I have a W 33B Three and I don’t see one. 


On Sep 8, 2020, at 12:02 PM, Allison Lehman via groups.io <allisonleh@...> wrote:

 I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640


<PastedGraphic-1.tiff>






On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David



Allison Lehman
 

The filters should be upstream of the injector pump.  That is thewwor job to protect the injector pump from getting clogged up.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 9:05 AM, chassidwa <chassidwa@...> wrote:

Do all injector pumps have built in filters? I have a W 33B Three and I don’t see one. 


On Sep 8, 2020, at 12:02 PM, Allison Lehman via groups.io <allisonleh@...> wrote:

 I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640


<PastedGraphic-1.tiff>






On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


<PastedGraphic-1.tiff>


chassidwa
 

My boat has the Racor between the tank, 10 micron, and a small filter between the lift pump and the injector pump, I recall that is??? 75 micron. That one I presume is in case the lift pump pukes impeller bits. 


On Sep 8, 2020, at 12:07 PM, Allison Lehman via groups.io <allisonleh@...> wrote:

 The filters should be upstream of the injector pump.  That is thewwor job to protect the injector pump from getting clogged up.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640


<PastedGraphic-1.tiff>






On Sep 8, 2020, at 9:05 AM, chassidwa <chassidwa@...> wrote:

Do all injector pumps have built in filters? I have a W 33B Three and I don’t see one. 


On Sep 8, 2020, at 12:02 PM, Allison Lehman via groups.io <allisonleh@...> wrote:

 I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640


<PastedGraphic-1.tiff>






On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


<PastedGraphic-1.tiff>


Jim Starkey
 

I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


chassidwa
 

How about a clean fuel container with a hose from the lift pump right into the container and see how she runs. If good then start working your way back to the tank. Between the lift pump and the injectors we have positive pressure so any leaks we would see fuel. 


On Sep 8, 2020, at 1:32 PM, Jim Starkey <Jim@...> wrote:



I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


Harry Keith
 

I am suffering similar but far less severe issues on my engine.  From a week off cold start, it takes 10 seconds of cranking to start (presumably air).  When running, I occasionally hear a slight stammer in the engine tone (not visible on the tach, but very audible to my ear).  I've checked all hose clamps, topped up the RACOR (first time I've used this model, and I didn't top them after servicing -- I'm learning), and looked sternly at most all connections.   I'm pondering how to diagnose further.

My reason to post is to share what I'm thinking of next.  It violates general best practices, ABYC, USCG, and probably US Law.  But it might help.

I'm considering taking out the last length of fuel hose (going to the injector pump) and substituting clear plastic hose.  I think it can take the fuel, the pressure (lift pump pressure only), and the engine room temp.  It will allow me to actually see what's going on -- lots of air, little bits, only when running fast, whatever.  I can't really see a REAL downside to doing this for a few weekends (unless the boat takes that opportunity to spontaneously burst into flames...).  Your problem is a bit more severe, so perhaps easier to diagnose -- when you find it, you fix it.  Mine, being very occasional, takes a weekend to decide if my latest attempted fix did or didn't work.  Being able to look at the fuel flow would be helpful.

Harry


On Tue, Sep 8, 2020 at 2:06 PM chassidwa <chassidwa@...> wrote:
How about a clean fuel container with a hose from the lift pump right into the container and see how she runs. If good then start working your way back to the tank. Between the lift pump and the injectors we have positive pressure so any leaks we would see fuel. 


On Sep 8, 2020, at 1:32 PM, Jim Starkey <Jim@...> wrote:



I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


David Short, SV One Timer, 1997 362, Mt Desert, ME
 

Rebuilding my injectors made a big difference in starting for me


On Sep 8, 2020, at 10:21 PM, Harry Keith <sailor11767@...> wrote:


I am suffering similar but far less severe issues on my engine.  From a week off cold start, it takes 10 seconds of cranking to start (presumably air).  When running, I occasionally hear a slight stammer in the engine tone (not visible on the tach, but very audible to my ear).  I've checked all hose clamps, topped up the RACOR (first time I've used this model, and I didn't top them after servicing -- I'm learning), and looked sternly at most all connections.   I'm pondering how to diagnose further.

My reason to post is to share what I'm thinking of next.  It violates general best practices, ABYC, USCG, and probably US Law.  But it might help.

I'm considering taking out the last length of fuel hose (going to the injector pump) and substituting clear plastic hose.  I think it can take the fuel, the pressure (lift pump pressure only), and the engine room temp.  It will allow me to actually see what's going on -- lots of air, little bits, only when running fast, whatever.  I can't really see a REAL downside to doing this for a few weekends (unless the boat takes that opportunity to spontaneously burst into flames...).  Your problem is a bit more severe, so perhaps easier to diagnose -- when you find it, you fix it.  Mine, being very occasional, takes a weekend to decide if my latest attempted fix did or didn't work.  Being able to look at the fuel flow would be helpful.

Harry

On Tue, Sep 8, 2020 at 2:06 PM chassidwa <chassidwa@...> wrote:
How about a clean fuel container with a hose from the lift pump right into the container and see how she runs. If good then start working your way back to the tank. Between the lift pump and the injectors we have positive pressure so any leaks we would see fuel. 


On Sep 8, 2020, at 1:32 PM, Jim Starkey <Jim@...> wrote:



I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


David Wall
 

Thank you all for the suggestions.  I did take apart the Racor and change the filter and gaskets,  I may take it apart again. It will be next week before I can get to the boat and continue my "adventure."
 I will let you all know how it goes.

Harry, My engine was hard to start when cold.  I changed out the glow plugs, now it starts instantly, just wish I could keep it running for more than 15 minutes.

David
Take 5
Sabre 34 #417

On Wednesday, September 9, 2020, 06:56:47 AM EDT, David Short, SV One Timer, 1997 362, Mt Desert, ME <dhs.short@...> wrote:


Rebuilding my injectors made a big difference in starting for me


On Sep 8, 2020, at 10:21 PM, Harry Keith <sailor11767@...> wrote:


I am suffering similar but far less severe issues on my engine.  From a week off cold start, it takes 10 seconds of cranking to start (presumably air).  When running, I occasionally hear a slight stammer in the engine tone (not visible on the tach, but very audible to my ear).  I've checked all hose clamps, topped up the RACOR (first time I've used this model, and I didn't top them after servicing -- I'm learning), and looked sternly at most all connections.   I'm pondering how to diagnose further.

My reason to post is to share what I'm thinking of next.  It violates general best practices, ABYC, USCG, and probably US Law.  But it might help.

I'm considering taking out the last length of fuel hose (going to the injector pump) and substituting clear plastic hose.  I think it can take the fuel, the pressure (lift pump pressure only), and the engine room temp.  It will allow me to actually see what's going on -- lots of air, little bits, only when running fast, whatever.  I can't really see a REAL downside to doing this for a few weekends (unless the boat takes that opportunity to spontaneously burst into flames...).  Your problem is a bit more severe, so perhaps easier to diagnose -- when you find it, you fix it.  Mine, being very occasional, takes a weekend to decide if my latest attempted fix did or didn't work.  Being able to look at the fuel flow would be helpful.

Harry

On Tue, Sep 8, 2020 at 2:06 PM chassidwa <chassidwa@...> wrote:
How about a clean fuel container with a hose from the lift pump right into the container and see how she runs. If good then start working your way back to the tank. Between the lift pump and the injectors we have positive pressure so any leaks we would see fuel. 


On Sep 8, 2020, at 1:32 PM, Jim Starkey <Jim@...> wrote:



I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


chassidwa
 

I like the idea of clear fuel lines, for diagnosis, to see if or where air is entering. 


On Sep 9, 2020, at 10:56 AM, David Wall <david.wall@...> wrote:


Thank you all for the suggestions.  I did take apart the Racor and change the filter and gaskets,  I may take it apart again. It will be next week before I can get to the boat and continue my "adventure."
 I will let you all know how it goes.

Harry, My engine was hard to start when cold.  I changed out the glow plugs, now it starts instantly, just wish I could keep it running for more than 15 minutes.

David
Take 5
Sabre 34 #417
On Wednesday, September 9, 2020, 06:56:47 AM EDT, David Short, SV One Timer, 1997 362, Mt Desert, ME <dhs.short@...> wrote:


Rebuilding my injectors made a big difference in starting for me


On Sep 8, 2020, at 10:21 PM, Harry Keith <sailor11767@...> wrote:


I am suffering similar but far less severe issues on my engine.  From a week off cold start, it takes 10 seconds of cranking to start (presumably air).  When running, I occasionally hear a slight stammer in the engine tone (not visible on the tach, but very audible to my ear).  I've checked all hose clamps, topped up the RACOR (first time I've used this model, and I didn't top them after servicing -- I'm learning), and looked sternly at most all connections.   I'm pondering how to diagnose further.

My reason to post is to share what I'm thinking of next.  It violates general best practices, ABYC, USCG, and probably US Law.  But it might help.

I'm considering taking out the last length of fuel hose (going to the injector pump) and substituting clear plastic hose.  I think it can take the fuel, the pressure (lift pump pressure only), and the engine room temp.  It will allow me to actually see what's going on -- lots of air, little bits, only when running fast, whatever.  I can't really see a REAL downside to doing this for a few weekends (unless the boat takes that opportunity to spontaneously burst into flames...).  Your problem is a bit more severe, so perhaps easier to diagnose -- when you find it, you fix it.  Mine, being very occasional, takes a weekend to decide if my latest attempted fix did or didn't work.  Being able to look at the fuel flow would be helpful.

Harry

On Tue, Sep 8, 2020 at 2:06 PM chassidwa <chassidwa@...> wrote:
How about a clean fuel container with a hose from the lift pump right into the container and see how she runs. If good then start working your way back to the tank. Between the lift pump and the injectors we have positive pressure so any leaks we would see fuel. 


On Sep 8, 2020, at 1:32 PM, Jim Starkey <Jim@...> wrote:



I think it's worse than that.  If I remember correctly, Jamie Frankel was plagued by an air leak somewhere in the pickup tube inside the tank.  I expect he will chime in sooner or later with the details.

On 9/8/2020 12:02 PM, Allison Lehman via groups.io wrote:
I agree with Charles start at t he tank and work your way to the engine then back to the tank.  IFyou can’t find any air leaks then you look at your fuel filters and then lastly and sadly  look for crud in your injector pump.

Allison Lehman
Swiftsure Yachts
allison@...
Cell: 510.912.5800
Fax: 510.860.4640








On Sep 8, 2020, at 8:37 AM, chassidwa <chassidwa@...> wrote:

How about from the tank to the Racor and any issues with the Racor itself? 


On Sep 8, 2020, at 11:30 AM, David Wall <david.wall@...> wrote:



I am continuing to get air in my fuel line.  The engine runs fine for a while especially at low RPM but if I increase the RPMs, it doesn't take too long before the engine starts to sputter and run very rough.  If I bleed the engine at the injectors it will run great again for a little while.  I have replaced the electric lift pump and the hoses from the lift pump to the fuel filter and from the filter to the injector pump.  I have taken apart, inspected and tightened all of the fuel filter connections and I have tightened all of the connections all the way back to the fuel tank. Also tightened the connections on the fuel return line.

I'm not sure what to do next.  Any suggestions would be much appreciated.

David


-- 
Jim Starkey


rich.ames@...
 

David,
If your issue is with fuel tank pick up, I have a spare pick up that I saved after I replaced the tank on my ‘88 S36.  I believe the 34s and 36s during that era used the same 20 gallon fuel tank...others may be able to verify.   


James L. Frankel
 

OK, Jim, I'll bite.

So, my air in the fuel line is a saga, but I'll spare you all of gory details and briefly summarize.  I was plagued by an engine issue for two seasons.  The problem would evidence itself only after more than eight hours of running the engine at cruising speed.  At first a barely audible slight loss of engine RPMs could be heard, but not seen on the tachometer.  After many some more hours, the loss of RPMs would become more noticeable until after even more hours on multi-day passages with little wind, the engine would convulse and shut down.  We investigated many possible causes besides air in the fuel, but settled on the air theory as most likely.  We noticed that the problem only appeared when then fuel tank was, say, less than 1/3 full.  The usual advice to run the engine directly from an open (and clean) fuel container bypassing all of the fuel system (filters, vacuum gauge, hoses, etc.) closer to the fuel tank than the engine's lift pump (we have a Yanmar) was not possible because of the offshore conditions and the length of time the engine would have to run.  We checked all appropriate connections for possible air intrusion into the fuel system, but didn't find any.  I used a camera to look inside the fuel tank and it was pristine.  Finally, after dealing with this issue for two seasons, we decided to disconnect the fuel line from the engine and also at the fuel tank.  After draining the fuel from the fuel assembly before the engine, I plugged one end of the fuel assembly and I built an adapter so that I could use a hand fender pump to pressurize the fuel hoses and we used a mechanic's stethoscope to listen for the high-pitched noise of escaping air at every connection.  We were sure that this would find the issue.  It didn't.  We felt very sad.  At this point, Lori said to me, "why don't we just finish the task and take apart the fuel tank, too."  I removed the fuel tank fuel pickup tube and the right-angle fitting into which it screws.  The right-angle fitting is an interesting component: it has inside threads where the pickup tube screws into it and it was outside threads around the inside threads where the right-angle fitting screws into the tank.  Of course, it also has a hose barb fitting at the end of the right-angle portion for the fuel hose.  We pressurized the right-angle fitting with pickup tube assembly and lo and behold, Lori heard a high-pitched whine where the pickup tube is screwed into the right-angle fitting!  Success!  My best guess is that after years of diesel sloshing around in the tank, it dissolved the thread sealant that had been applied to those threads -- at that point there was no visible sealant.

There are several observations that I'm able to make a posteriori: (1) it seems that when there was a high level of fuel in the tank, there was sufficient fuel that would splash onto the right-angle fitting to effectively seal the very minor gap, (2) after finding the problem, I was able to find articles written about how a minor air leak prior to the primary Racor filter assembly will over time develop an air pocket in the top of the filter assembly.  Only after a long time will the air pocket become large enough that it becomes low enough in the filter assembly for some of the air to be drawn out toward the lift pump and into the engine.  In our case, this took a very long time.

So, I suggest that you purchase a mechanic's stethoscope and pressurize your system and listen for air leaks.

Jamie Frankel
S/V Sea Quester
2003 Sabre 362
www.seaquester.com