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Old 01-19-2021, 09:40 PM   #1
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Chasing air in fuel line two years

I have been writing this for two years in my head, but wanted to exhaust every troubleshooting skill I have (not much evidently) before posting.* Our boat has two John Deere 4045 engines with standard primary and secondary engine* fuel filters, supplied by the standard Racor 500 series dual manifold turbine fuel filter (Racor) with selector valve and vacuum gauge, supplied by a keel ďday tankĒ about 3-4 feet below the engine.* We also have a fuel polishing pump and enough valving / piping flexibility to pump / pressurize wherever we need to.

Because the day tank is below the engine and filters, there is a small 2*+- psi vacuum in the fuel lines when the engines are off.* I learned early in our ownership that after leaving the boat for a week or two the port engine would start, run for about 10 seconds, then die (perhaps about the right time air in the secondary filter could*get to the injector pump).* I would then need to bleed the engine secondary filter to get things started.* So I went through all lines, pressurized and looked for fuel leaks, and replaced a suspect gasket or two.* Nothing changed.* I then started closing the ball valve feeding the engine from the Racor 500 thinking this would eliminate the vacuum and thus air infiltration.* Nothing changed.* So I started using our polishing pump to pressurize the fuel lines and this helped and now no problems leaving the port engine for a month or so.* Inconvienent, but at least I had a work-around.

So, last fall I had my work around in play after the boat sat for about 6 weeks and there was still about 1/2 psi positive pressure in the lines (pressure very slowly leaks off over time).* I open all the valves, hit the starter, and it runs for 1 second or so.* Doesn't want to restart.* I am able to restart by pressurizing*the fuel line to about*3 psi for a 10 second crank.* This is the first time it has quit after 1 second.

Here is what I know:
-The engines always start immediately*- like the first cylinder.

-I've tried feed from both sides of the Racor 500 thinking gasket leak, no difference. Replaced all gaskets. No change.

-In fuel lines/fittings air can pass through very tiny leaks when fuel might not.* Or, just because I can't find fuel seeping out at 2 psi does not mean that air might be leaking in at -2 psi vacuum.

-If fuel line pressure can be maintained at even a very small psi in the lines no air can seep in.* Right?* Right???

-The starboard engine does not have the same problem unless left for 6 months or so.

-I'm really frustrated.

Has anyone else chased air like this, and did you finally find out what was going on?* I'm to the point I will need to call the John Deere mechanic, but they are located 4 hours (round trip) away and I hate not being able to figure out what should be a simple problem / solution.* Also, what would they do that I have not tried already?
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Old 01-19-2021, 09:59 PM   #2
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What kind of fuel lines do you have? I replaced my Racor 900FG last year with a 900MA and a built in priming pump. I sealed all metal to metal fittings with MarineTex. I know it is permanent but since I donít have any air or fuel leaks I donít care. Even if I have to replace a fitting down the road, it isnít that big a deal. If you have fuel hose instead of copper for fuel lines, have you replaced the hose? Sometimes the inside starts to break down and it still looks good on the outside. I am ready to replace the other Racor later this week and also used MarineTex to seal the metal fittings. I clean all the fittings well and then use the MT. It comes out around the joint so I can tell the joint is sealed well. You donít want to use teflon tape on a diesel system. After all the work you have done and not found the problem, I think I would maybe rip the supply lines apart and start new. Use new hose and seal the metal fittings well. Do it methodically and make sure every fitting is well sealed. Good luck.
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Old 01-19-2021, 10:09 PM   #3
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Last year, we chased a similar problem on our TransPac Eagle 32. We had a dual Racor 500 set up installed by a PO and could switch from one Racor to the other on the fly. This system was pieced together with brass fittings and rubber fuel hose and stainless hose clamps and sounded like the ideal system when I first saw it. Our issue was that the active Racor would eventually fill with air and kill the Lehman SP90. We chased the issue for a number of months and even after replacing the old Racors couldn’t solve it. Finally, we ended up putting an electric fuel pump in line near the fuel tank, the issue is solved.

The diagnosis: The Racors sit about 27 -30 inches above the bottom of the pickup tube in the tank coupled with the head loss and fuel line friction, the mechanical pump on the Lehman would suck in air, invery small amounts, past one or more hose barb/clamp fittings and finally displace the fuel in the Racor. The electric lift in the system pushes rather than sucks the fuel and no air is introduced.

In the case of a tank being 3-4 feet below the engine pump, every connection in the system will have to be 100% sealed to prevent air or loss of vacuum on the system. If you have any hose barb/clamp connections in line, they would be suspect.

All during our search for the issue, we never saw one “leak” in the system. This is because air is much thinner than fuel and can leak in where fuel won’t leak out.

Hope the helps.
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Old 01-19-2021, 10:16 PM   #4
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I'm no diesel mechanic but one thing I've had trouble with is the fittings with copper crush washers. They're supposed to be a one use item, replacing the washer every time you loosen the bolt. I doubt many people actually replace every time, but eventually they will leak. Don't try to stop the leak by tightening the bolt, usually they're hollow with a hole drilled in the side, you'll just snap it off. And right, air will leak into a hole that fuel won't leak out of, so these leaks can be the devil to find.
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Old 01-19-2021, 10:27 PM   #5
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Quote:
Originally Posted by Eagle Pursuit View Post
Last year, we chased a similar problem on our TransPac Eagle 32. We had a dual Racor 500 set up installed by a PO and could switch from one Racor to the other on the fly. This system was pieced together with brass fittings and rubber fuel hose and stainless hose clamps and sounded like the ideal system when I first saw it. Our issue was that the active Racor would eventually fill with air and kill the Lehman SP90. We chased the issue for a number of months and even after replacing the old Racors couldn’t solve it. Finally, we ended up putting an electric fuel pump in line near the fuel tank, the issue is solved.

The diagnosis: The Racors sit about 27 -30 inches above the bottom of the pickup tube in the tank coupled with the head loss and fuel line friction, the mechanical pump on the Lehman would suck in air, invery small amounts, past one or more hose barb/clamp fittings and finally displace the fuel in the Racor. The electric lift in the system pushes rather than sucks the fuel and no air is introduced.

In the case of a tank being 3-4 feet below the engine pump, every connection in the system will have to be 100% sealed to prevent air or loss of vacuum on the system. If you have any hose barb/clamp connections in line, they would be suspect.

All during our search for the issue, we never saw one “leak” in the system. This is because air is much thinner than fuel and can leak in where fuel won’t leak out.

Hope the helps.
My new boat has a boost or priming pump that 'sucks' through two filters. Bad design, too many fittings on the suction side. I'm going to reroute so the pump pushes rather than sucks through the filters. I don't know if it was ever a problem for the PO, but I'm not taking the chance.
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Old 01-19-2021, 10:39 PM   #6
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Be suspicious of valves. Gate valves have a seal/packing around the handle shaft under a pressure nut that can leak air yet not leak fuel. Ball valves are far less prone to this but not immune.

Flare fittings can pickup a tiny scratch which can cause air to be allowed into the system.

If the engine has a lift pump on the engine block they can leak air as the diaphragm or gaskets age.

Have you tried a piece of clear vinyl tubing installed in the fuel line to track air leaks? Install it in the line near the injection pump. Install with a loop so not only are the bubble seen but trapped so there is no doubt. You may want to leave enough slack that you can move the loop so initial bubbles can be purged. Purge the system and start the engine. Likely there will be some bubbles still pass but they should stop if the system is tight. THen purge the loop. Watch for a few minutes. Race the engine somewhat to increase any vacuum generated.

If bubbles still show then move it to the next item upstream towards the tank. Same deal. When and if I am assuming you find no bubbles after moving the tube just past an item then the item you just passed is likely the problem.
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Old 01-19-2021, 10:45 PM   #7
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"-If fuel line pressure can be maintained at even a very small psi in the lines no air can seep in.* Right?* Right???"

Just to confirm, this is always vaccuum, right? How are you measuring it? In vacuum any decrease could be caused by air infiltration.

Not an expert, but it sounds like you have a leak on the motor side of the guage. Check gaskets on OEM fuel filters, fuel pump, etc.
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Old 01-19-2021, 11:25 PM   #8
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For air to displace fuel, the fuel has to go somewhere. Back to the day tank which is the low point? Is the vacuum in the day tank because that vent is closed?
Fittings at the pressure pump. How about the connections to the injectors under the valve cover. If you are not seeing fuel, not losing it then the input for air must be higher than the day tank. IMO
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Old 01-20-2021, 02:42 AM   #9
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Because the day tank is 3-4' below the engines the fuel is always going to be a vacuum. Put a valve at the Racors and shut it anytime the engines are off. The valve can be electric and open anytime the key is on.
With the valve closed, the fuel on the Racor side will stay where is is and won't draw in air. The fuel before the valve will try to go back, but it doesn't matter. When you start there's enough volume in the Racor to separate out the air. You may need to vent the air from the top of the Racor from time to time.
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Old 01-20-2021, 07:17 AM   #10
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I would install a rubber pump as found in most outboards at the tank , pressurize the lines and filters and wrap every joint with paper toweling .

The leak should show it self in time .

If the leak is only when the lines are under suction the chase becomes harder.

Usually only one size of tubing is on a fuel supply system , so go to a large commercial refrigeration shop and purchase an armored site glass.

These will show bubbles in a liquid flow , so you will need to install it at different places. Fairly easy as they are built with a male and female end , so can be placed easier.

A load of work compared to simply installing a DC priming pump.

I hope the ever vigilant thought police will not send me for re education for noting male and female ends.

I have no idea on todays proper gender free modern term.

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Old 01-20-2021, 08:18 AM   #11
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I have the same 4045 engine, although not with your lift configuration. The specification sheet for the engine has a maximum lift height to the pump of 7'.

How many hours are on the engine and has it always done this? What height is the Racor below the lift pump or above the tank? Is this the original lift pump? Does your Racor have a vacuum gauge on it? Have you replaced all the orings on the Racor (bowl seal, drain seal, lid, lid retaining bolt, inlet and outlet adapters). Did you check the check valve ball in the Racor (I believe it has one like the 900 and 1000 series)?

If I were diagnosing the problem, I would start with where the air is accumulating. I really don't think it's in the secondary filter after the lift pump as there are 2 check valves in the lift pump to prevent that. As quickly as it quits, I would guess you will find the air in the primary filter just before the lift pump or the Racor. Because of the fuel plumbing design, I would let the engine sit unit you're sure it has lost prime, and then open the Racor to see if there is air in the filter compartment. If not, then pull and check the primary on the engine. Knowing where the air is collecting will help to diagnose where the leak is.

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Old 01-20-2021, 09:14 PM   #12
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Thank you all for responding. You have given me several new ideas and I will press on.

To clarify a few things you all brought up:

- We never have problems while under way or on the hook over night and under way the next day. Only have problems when boat sits for a few weeks.

- Yes, Racor O rings and gaskets have all been changed many times. That said, we do collect air in the upper half of the filter over time. Is this normal?

- We have no gate valves, only ball valves.

- Line pressure or vacuum is being measured by the guage on the Raccor 500. About 2psi vacuum under way and normal engines off, or 3psi pressure if I pressurize system for long periods of sitting.

- "Somewhere South of Disorder" as a location - best line ever!

- Piping is copper to Racor, rubber to engine primary filter, steel thereafter

- Engine hours 1400. Good idea checking for air before I start engines in each filter housing

- Day tank vent working and not plugged

Again, thanks everyone.
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Old 01-20-2021, 11:11 PM   #13
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Air collecting in the upper half of the filter over time IS NOT normal!
If the "rubber hose" is just upstream of the primary filter, and all other fuel line is steel or copper, I suspect that the problem is your rubber hose, or the rubber hose connections. I would replace it, especially if you don't know the age of the hose. Those rubber hoses are necessary in order to isolate vibration between the engine and the rest of the boat, but often they look perfect, but are deteriorated, as mentioned in an earlier post. Replace it, and while you're at it, replace the same hose on the other engine at the same time! Please keep us advised as to what you do and what happens. Take care, and good luck!
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Old 01-20-2021, 11:24 PM   #14
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If air can get in on a visible part then fuel under should be able to escape in use. IMO
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Old 01-21-2021, 12:27 AM   #15
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Agree about the hoses.

I have only one tiny Racor without what I write about so no personal knowledge here.

However, one note about Racors. Racors , some, have a check valve in them that has a removeable seat. The seat is marked to indicate which side is up .

The marking is apparently very slight so easily missed. The difference in the washer faces is very slight also which means people miss that. The result is people install that seat the wrong way around which causes problems "similar" to what you are experiencing. THe seat orientation does matter.

THis was written about many times on Boatdiesel over the years which is why it stuck with me. I simply forgot about it untill now.
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Old 01-21-2021, 01:00 AM   #16
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I like to learn. Page 7 item #7
https://www.parker.com/literature/Ra...ine_Series.pdf
Page #1 talks about install a check valve into the line if the tank is lower than the racor. Think we found the problem.
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Old 01-21-2021, 09:11 AM   #17
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One last thing I forgot to mention, you have 2 leaks. The first is the air leaking into the system and the second is the fuel leaking out.

The fuel leaking out triggers the air leaking in as fuel isn't compressible and without the fuel leaking out, there would be no space for the air. If you're not finding fuel around your system, it's likely leaking back into the tank. The below picture of the Racor 500 shows the internal inlet check valve which is the ball to the left of the number "2". That ball floats up against a seal to prevent fuel from leaking back into the tank. If you haven't already, remove the ball and seal by unscrewing the diffuser on the bottom. Clean inspect and reseal to make sure the check valve is functioning properly.

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Old 01-21-2021, 09:57 AM   #18
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You've received some good comments and suggestions. Questions:
- Are all your fuel tanks below the fuel lift pump or is it just the day tank?
- Do you have a fuel manifold to isolate tanks?
- To which tank does fuel return go?
- Can you bypass the day tank?

It seems the fuel piping routing and tank locations are in question. Ideally, a vessel should be able to sit for a very long time with no fuel departing the system. Work arounds are OK, but assessing design flaws, construction gotchas and fixes may prove worthwhile.
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Old 01-21-2021, 10:39 AM   #19
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Take some advice from diesel fire pump engines. John deer is often used by Clarke as a fire pump engine.

The fire pump code specifically requires the fuel supply to be above the engine lift pump. In other words your day tank arrangement would be against the law for the very reason you are having problems. See attachment from NFPA 20
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Old 01-21-2021, 01:33 PM   #20
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Without pictures and with a large dose of conjecture, a couple of questions: A single 500 Racor to feed two engines? Does it also feed the genset? I think (without researching Racor) that is too small for 2 or 3 engines. If you select 'both' filters, does it eliminate the vacuum reading? I would read up on the specs and start looking for a pair of 900s or my favourite, the 1000s. Or get another pair and separate the systems for each engine. Best solution! Right now if a filter clogs, both (3?) engines will quit before you can switch over.

Is the main tank higher than the engine? If so, gravity should feed the fuel adequately all the way to the engines.

Does the day tank stay full like a fat fuel line or does it have a float switch?
Where does the fuel return line go? To the day tank or the main(s)?

There should be no vacuum measured at the filter with the engine off. You need positive fuel pressure (gauge reads 0) either from gravity or a pump. The gauge should be at zero except while running, then only show some vacuum if the filter is clogged or partially blocked. The vacuum is only supposed to show the condition of the filter. Change the filter if you haven't, then check the flow from the tank to the filter. Any pumps should be downstream from the filter not above (except as a filter primer, in its own valved loop) but gravity should fill the filters. With the fuel level above the engine, if you remove the fuel line from the secondary filter, does fuel flow freely from it? It should.

You might try running a line from the Racor directly to the engine to see if that eliminates the air leak.
Don't install an outboard type of pump, they are not certified for engine room use. For testing only, go crazy.

Is the day tank to hold extra capacity or is it used as a manifold? If not required for capacity, I would bypass it and run a line to each motor with its own dedicated filter and return the bypass fuel to the main tank. Also, install a cross-over in case one supply is compromised. This would simplify things greatly and simplify troubleshooting.

Good luck and let us know!
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