air in fuel system

[Seas the Moment]

Sending this to all you DD gurus. I have 8v92TIs. Port engine will start and run fine for a short period of time and loose RPM and stop. I checked the "screw-on" secondary fuel filter (must not be original) and it was half full of fuel. So, I filled it with fuel to displace the air, reattached and with a bit of starter turnover, she fired back up. Again for a short period of time. I did this 4-5 times. I then turned on the primer pump (again added by PO) for the port side and ran that for 10-15 minutes. She fired up and ran for 15 minutes. I took her out for her maiden spring voyage up the York River and guess what? About 30 minutes into the trip...yup down she goes. I locked the port drive line with a 12" pipe wrench and ran with just the starboard engine to Mobjack bay. I decided to run the primer pump on port side while underway and tried to fire the port back up while underway. She fired up, off came the pipe wrench and we ran for 24 minutes with 2 wheels...yup down again. Pipe wrench back on drive line on port, ran with one engine. Primed one more time as I entered the North river in Mobjack to anchor (thought it would make sense to have 2 engines for manuevering in tight quarters) Anyway, both engines ran for 40+ minutes. Been running most of the time at 1200 RPM. I took them up to 1500 RPM and noticed that the port would drop and raise 100+- RPM every 10 minutes or so while on syncro. Almost expected her to drop out again but she hung in there and seemed to "level off".

Very important note: I was analyzing the fuel manifold system and the placement of the primer pumps for port and strbd. Here is what I have: coming off the manifolds on the line out to the respective engines there is a "T", off the "T" it goes to the input of the primer pump. From the primer pump the output goes to another "T". Between the 2 "Ts" is a ball valve. So, coming from manifold to engine: "T", ballvalve, "T". When the ball valve is open and prime pump is turned on she is pumping as fast as she can. When I close the ball valve, she obviously is building pressure and you can hear the primer pump labor, slow rpms and I noticed the pressure gauge on the racors for the port engine increase to about 4-5 psi. I see no check valves within the "T-ball valve" configuration at the primer pumps. I am assuming with the ball valve open, the primer pump sees no resistance since it can pump within a circular motion within the "T-ball valve" configuration. Note also, that when I turned on the primer pump while underway, I would run the primer with ball valve open, then close and build 5psi on racor gauge prior to firing engine back up and getting 20+ minutes of consistent run.

I tightened the racor lids very tight, thought I might be sucking air, checked fuel fittings for obvious leakage (where could be sucking air) none.

I am hopeful someone out there in HOF-land has an answer. Don't really like the idea of pulling back into York River Yacht Haven in Glouster Point and docking on one engine...bow thruster or not!

I also have to tell you all how invaluable this forum is. I am on this site at least every other day and the wealth of information gleamed from you all is incredible. Honestly, besides the fact that the Hatteras is one of the finest boats ever built, this forum and the sharing and willingness to share is reason enough for me to never buy any other boat but a Hatteras.

Thanks for all your help.

Loran

 

[Bob Bradley]

Check the "screw on" filter to make sure that there is only one gasket in place. Sometimes when removing the old filter, the gasket comes off the old filter and stays in the fitting. When the new filter is screwed on, the two gaskets come together and don't seal properly.

If that's not it, I think I'd have a long section of flexible fuel line made up and use it to bypass each section of your boat's fuel system until you find the section that is causing the problem. Hook one end up to the inlet to the secondary, and the other end to the inlet to the primary, so you bypass that portion of the system.

If the probem persists, the air leak is before the primary; if not, it is either the primary or the line between the primary and secondary. Work your way back through the system.

 

[Avenger]

If you make up a test line like that, use clear tubing. That way you can see the air. Makes diagnosis much faster.

 

[REBrueckner]

Did you change the settings on your fuel manifold....like switch to a different fuel tank just before this problem started??? The valves can leak air.

What work if any was done on the fuel system immediately before this problem arose? look there first.

Bobs idea, bypassing sections, has to be used carefully ....check out the following to see if the " logic" is there....
//////////////////////

Seems like you should be able to tell if the air leak is before or after the fuel primer pump, but I have never used one, so maybe others can confirm or deny this approach:

If the air leak is on the INTAKE side of the fuel primer pump, when it runs it should suck air in and you should see air bubbles with any fuel dribble out of a loosened connection, right?

Like maybe loosen the fuel output on the engine side of your secondary fuel filter....Or you could hook up SCRODS clear line to the fuel pump output side and observe.....if clear, no bubbles, go to step two:

If the air leak is on the OUTPUT side of the fuel primer pump, an observed fuel dribble as at the output of the secondary filter should have no air...just fuel....and if pressure builds from the primer pump, shouldn't some fuel drip OUT of the air leak spot??

Diesel fuel is sometimes tough to see in a dimly lit engine room: I have found wiping each connection with a white paper towel and using a local light, droplight or flashlight, picks up fuel drops I never otherwise saw.

good luck....

 

[Timm]

I had a devil of a time tracking down an airleak when I first purchased our 53yf and spent a small fortune doing so as well.

I could see air bubbles escaping from the turbine so had a pretty good idea the issue was something on the supply side. There were no other external indications of leaks.

It turned out the primary reason I was losing prime were leaking manifold supply valves for all 3 tanks. Apparently the seats/seals which are metal on metal were completley worn out allowing just enough air to enter the system eventually draining the Racors.

Part of the "fortune" I spent was installing the Racor priming pumps that attach to the Racor's but have been worth every cent and were a godsend for quick priming if the engine died. They also are a huge advantage when re-filling the Racor's after changing elements.

Bottom line, consider changing the supply valves to eliminate a current or future air leak. The valves are relatively inexpensive, easy to change and you'll love the ease of moving their position from tank to tank as compared to the originals. If your's are like mine, they were quite stiff.

 

[hibanx]

It could be a fuel pickup tube in the tank. Did the problem start after the fuel level in the tank went down? It could be a pinhole in the pickup tube that sucks air when the fuel level drops below it. Try filling the tank completely and see if it cures the problem. It could also be a restriction caused by debris on the pickup tube.

 

[TopHattandTails]

I'm in year 3 of chasing this gremlin. I loose prime at rest in the Racor, not while running. It appears to get worse with use. I replaced the Racor first. It was fine, then it took 2 weeks to reappear, then 1 week, then 4 days, then 5 hours... Then I went to Hatt School. Fairly common that the manifolds (as Timm indicates). In process of a new manifold. We'll see. Next move is the fuel line from the Racor to tank. I found that by turning the manifold to off for that supply, it held prime. Tipped me off towards the manifold. But this winter, before I tore apart the manifold, I lost prime in the off position. Makes me wonder... We'll see...

 

[Canuck Dennis]

You are not supposed to ever pump fuel to the racors it will emulisify the water into the fuel so I am told by Parker Hannifin. ONly use it to prime the filter after a change and fill the container before putting in the new element.

 

[Seas the Moment]

WOW! And I thought I had nothing to do this weekend!

Thanks for all the suggestions and guidance. To answer some of the many questions within the answers:

- Looked, only 1 gasket not 2 at secondary spin on filter.
- I did change over the valves to different tank at end of season, so that may have aggravated the problem.
- Tanks were filled to the brim at end of season for the winter, so I don't think I have a pin hole issue...at least it wouldn't show now with full tanks.

I am leaning toward the manifold valve sucking air suggestion. They were very stiff. Anyone purchase new ball valves in the past with good results and from what company?

Looks like I got a lot of investigating to do. I will keep you posted so we all learn exponentially.

Thanks again!

Loran

 

[Timm]

The manufacturer is Apollo and they can be ordered from your local West Marine or on line.

 

[yachtsmanbill]

If you have shut off at the tanks, kill those and put a vacuum source with a gage at the racor inlet hose connection. If yours has check valves like mine, include those in the test. It should hold absolute unless the shut off valve leaks. Then youll need to disconnect that and cap it.
My bet is on the manifold valves. I believe the OEM valves are sealed with O rings that get hard and leak, especially if they are disturbed. ws

Check valve is the silver fitting on the right side. While yer there, check the hoses to the manual primers too!

 

[Seas the Moment]

Ok folks, as promised... my follow-up: I checked the secondary filter gaskets once again to ensure there was only one, yup. And BTW, it was once again half full of fuel, again. I did wipe the gasket clean, check the metal seat for any debris and nicks, none, wiped it clean. Refilled the secondary, reattached and tightened very well. Next went to the manifold, turned the supply/return ball valve for port engine from forward to rear tank. I ran for 2+ hours with no issues with no air in line. Note Strb ball valves supply/return are on forward tank. So, I have to believe there is an issue with the line from the forward tank to supply ball valve for port engine, or bad valve and moving it simply help "re-seat" the seal. But, what do I know...Yuz guyz are the experts. Thoughts?

Thanks, Loran

 

[TopHattandTails]

Damn thing still leaks air!!!

Ok- short story catch up. Would run the boat and stbd Racor would drain back. I rebuilt, then replaced. Same issue would drain back while at rest. This past winter I replaced the suction side manifold. Now the problem is worse. The Racor looks like an F4 tornado with air ,coming out of the air separator in the Racor and bogs down at 1600rpm. If I let it idle, it stalls after 10 minutes or so. This week I replaced the suction lin from the pick up tube to the manifold (no USCG blue hose) and from the manifold to the Racor is now USCG blue hose. All copper is gone. Still leaks air, but not as bad. The 3rd fuel line is coming out this weekend.... Both motors show air. The stbd side, aft Tank suction is worse than stbd side fwd tank suction. ANY IDEAS? Fuel at tank shows 3/4 full both tanks. As Charlie Sheen would say "problem is winning".

BTW- the port side shows some air too. Is there supposed to be some air or none?

 

[Genesis]

There should be no air at all.

Did you check the selector valves? Other possibility is the pickup tubes.

 

[TopHattandTails]

Ugh. I was afraid someone would say the "p"word. You Think it's worth back flushing the suction side of the system at all? I have huge pressure (pull down pressure gauge is firmly in the yellow) at the Racor and running 55 -58 psi on the return side (which I think is low to average). Based on Genesis' comment, I wonder if there is some tank garbage stuck in the pick up... Just seams odd that when I replace the fuel manifold, it all goes jiberdeedue....(the fuel manifold connections have been checked). This issue must end.

 

[TopHattandTails]

There should be no air at all.

Did you check the selector valves? Other possibility is the pickup tubes.

the selector valves (aka manifold) arein the correctposition. I did replace the stbd suction valve this winter- thinking the seals were shot.
Both motors at the same time? I have each motor sucking and returning to separate tanks (they return to the same tank the suction from). Both motors are showing air. I'm gonna top off the fuel just to make sure it's not empty... Both tank gauges show over 3/4 full though...but stranger things have happened. The gauges have worked in the past - and to have both fail at the same time??? I just
Have a tough time believing that both pick up tubes rotted off at the same time and both gauges show 3/4 full, when it acts like it's Empty. Could it be dirty tanks and crap sucked up in both pick up tubes?

 

[Boatsb]

Is there a common element in the tank gages? maybe a single power source or ground that would cause them to both show wrong? can you access the tanks and check the fuel level through an inspection plate?

Sounds like low fuel level.

 

[sgharford]

I recently found air leak very quickly and rather painlessly on my generator 2 weeks ago with help of Mityvac Vacuum/pressure checker (see below, about $90). By cutting your fuel system in sections (ie - we're you can unscrew fittings to plug one end and insert pressure tester on other) you can quickly determine problem area by process of elimination. Comes with all sorts of rubber attachments for plugging and inserting pressure tester. I forgot I had this thing until the 'wtf now' moment when generator wouldn't start for first time after I rebuilt most of it over winter. Bought it 15 years ago to change brake fluid on motorcycle. Maybe you have one to in your tool cabinet already too.

 

[Bob Bradley]

I had an air leak problem last fall that I corrected this spring. Seems I had removed and replaced the the line from the pickup tube and in replacing it, got a paint chip in the flare fitting. That's all it took to screw the pooch.

Go back to the valves you replaced and check the job for dirt of possible cracked flare fittings.

 

[garyd]

I got an air leak in the generator fuel system. Fought it and it would run for 4 hours then 2 hours then one hour then 30 minutes. Changed the filter and you guessed it it would run for 4 hours then 2 hours then 1 hour etc etc.

I bought a new racor. This was after chasing every posible gremlin. When I changed to the new Racor and removed the fittings I found that there were two washers that was on one side one on the other. The washers were in place just to line things up and did not impede the seating of the flared fittings. That is one washer O.K. two washers no good and the flared fitting just didn't quite seat. So once I went to one washer per fitting problem immediately went away!