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Old 04-08-2019, 23:00   #1
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Air in fuel system

Recently I have encountered a recurring problem. Air is getting the fuel system when the engine is not running.
The symptoms : the engine, a Westerbeke 55-B, starts quite readily, no hesitation. However, after running about half a minute, it starts to slow down and run pretty roughly, as though it were fuel-starved. Sometimes it stops altogether, sometimes it clears up and runs normally until I shut it off, after 5-10 minutes or whenever, without a hiccup. Clearly this is a reliability issue that at minimum is embarrassing with guests aboard, and more serious in other circumstances.
Upon examining the Racor filter-water separator, the plastic bowl is half empty or possibly more. If I turn the ignition key on without engaging the start button, the pump functions as intended, pressurizing the fuel system, filling the filter bowl, and the engine starts and runs normally. However, after shutting down, and letting the engine rest for a couple hours or less, the filter bowl has drained and the symptoms re-appear. I have tightened the T handle on the Racor, and examined for fuel leaks, and have found none.
This problem appeared after changing the filter element, which I have done countless times over the last 20 years, always with no issues.
The only thing I can think of is that the check valve in the filter which keeps fuel in the filter from draining back into the tank has somehow become inoperative with gunk that the filter is designed to filter out.
But thatís only my unproven theory. If thatís the culprit, how do I resolve it?
And if itís not that, what is it, and how do I fixit? Smarter minds than mine surely know what to do.
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Old 04-08-2019, 23:57   #2
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Re: Air in fuel system

Check your fuel lines for small leaks, usually at the clamps. Fuel won’t be leaking out, but air is being sucked in. When was the last time your fuel hoses were changed?
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Old 05-08-2019, 00:14   #3
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Re: Air in fuel system

Also check your tank vent is not blocked. Non-return valves are very cheap so you could put another in the line.
But most likely is post #2 Check all the joints
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Old 05-08-2019, 00:42   #4
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Re: Air in fuel system

What Kenomac said. I had this, along with plugged pickup from tank sludge. Click image for larger version

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Old 05-08-2019, 05:45   #5
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Re: Air in fuel system

Have checked for air leaks. Not sure how I would spot one, (air would be sucking in, right?) but have rightened hose clamps. Could be theyíre over-tightened and have cut the hose, but it seems an out-flowing fuel seepage/leak would be apparent if that were happening. I realize it could be coincidental, but Iím puzzled why this problem would arise about the time I changed the filter element. The fuel intake line is about 10 years old, so it wouldnít hurt to change it, but an air leak in that would seem to imply that the problem appears when the engine is running. Air in the filter appears when the engine us NOT running.
I appreciate all suggestions.
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Old 05-08-2019, 06:06   #6
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Re: Air in fuel system

Sounds like an partially/intermittently plugged pickup tube in the tank. As it sucks more fuel, builds up vacuum in line and pulls air in. Disconnect and blow into intake hose to tank and see if it clears. Diesel doesn't taste too bad, I kind of acquired a taste for it when I was troubleshooting my system.
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Old 05-08-2019, 06:37   #7
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Re: Air in fuel system

Quote:
Originally Posted by Mickeyrouse View Post
Have checked for air leaks. Not sure how I would spot one, (air would be sucking in, right?) but have rightened hose clamps. Could be they’re over-tightened and have cut the hose, but it seems an out-flowing fuel seepage/leak would be apparent if that were happening. I realize it could be coincidental, but I’m puzzled why this problem would arise about the time I changed the filter element. The fuel intake line is about 10 years old, so it wouldn’t hurt to change it, but an air leak in that would seem to imply that the problem appears when the engine is running. Air in the filter appears when the engine us NOT running.
I appreciate all suggestions.
Did you change the two rubber o rings when you changed the filter? Diesel is sucked up into the engine and circulated back to the fuel tank, so you won’t see fuel leaking out of a cracked or leaky hose or leaky o ring. The fuel would simply siphon or flow back into your tank leaving an air filled hose.
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Old 05-08-2019, 09:18   #8
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Re: Air in fuel system

If visual inspection of the hoses, filters, joints etc doesn't reveal the problem what I do is work my way through the system step by step.


Get a small, completely clean jug or bottle and fill with completely clean diesel. If using a plastic bottle, make sure it's compatible with diesel and won't melt and leak.


For safety start before the final filter on the engine just in case there's any sediment or junk in the fuel. Disconnect the line going into the final filter and connect a hose from your fuel bottle to the filter intake. Crank and run the engine to see if the problem goes away. If the engine runs fine at this step then move one step in the fuel system farther from the engine and repeat the test. Keep doing this until the engine no longer runs and you have isolated where the problem is.
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Old 05-08-2019, 09:50   #9
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Re: Air in fuel system

The lift pump is almost certainly sucking air if it happens with the engine running. Depending on the Racor placement, the fuel leaks back to the tank, breaking the vacuum by sucking in air from somewhere in the lines,the Racor, or secondary filter.

Sometimes coating connections with light powder or toilet paper will reveal the leak. If all else fails, add a fitting the allows air to pressurize the fuel system and look or listen for leaks. You only need 5-10psi. a bicycle pump is enough.
One common hidden source for leaks is a place where the fuel line can rub with engine vibration. Not necessarily close to the engine. It can wear a tiny hole in a bracket or where the line is against a bulkhead or engine beds.
I have a small unused Racor 140 and it doesn't have a check valve, so fuel could drain back.







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Old 05-08-2019, 10:21   #10
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Re: Air in fuel system

Ok, this has been the vain of my existence.
Let me start by saying, I feel your pain.
My first problem, the Racor powder coating/paint was loose and allowing it not to seal. The seal on the bottom of the Racor was sucking in air as well.
The second problem. After the Racor was rebuilt ($60 for rebuild kit). The fuel line had a tremendous amount of vacuum on the hose and causing the fuel line to collapse.
The last problem, the 90 degree fitting on the pick up tube was getting clogged by organic material because the fitting when tightened decreased the size of the pickup tube hole to a very small size.
Made the hole bigger on the fitting, replaced the collapsing fuel line. Rebuilt Racor and started using the Power Service fuel additives products. No problems since.
Look at the line Power service products and get the Bio-Kleen as well as the centene replacement products, You will not be disappointed. Again, I feel your pain. Hard to dock a catamaran with one engine with two 90 degree turns with inches on both ends. Good luck.
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Old 05-08-2019, 10:53   #11
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Re: Air in fuel system

I have had problems with air leakage when I change filters.
I now smear Vaseline (it is pure petroleum jelly) on the filter body, element and gaskets whenever I change filters and have not had a problem in years, as the jelly helps seal and seat the gaskets on the filter body and element.
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Old 05-08-2019, 11:46   #12
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Re: Air in fuel system

Quote:
Originally Posted by Paul Howard View Post
I have had problems with air leakage when I change filters.
I now smear Vaseline (it is pure petroleum jelly) on the filter body, element and gaskets whenever I change filters and have not had a problem in years, as the jelly helps seal and seat the gaskets on the filter body and element.
Depending what the o-rings are made from this may not be a good idea. Vaseline will eat some rubbers. Better would be to use silicone.
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Old 05-08-2019, 11:55   #13
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Re: Air in fuel system

Start with a piece of clear hose at the tank and watch for bubbles. Keep moving the hose downstream until bubbles appear. That will tell you where the problem is.
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Old 05-08-2019, 13:07   #14
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Re: Air in fuel system

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Depending what the o-rings are made from this may not be a good idea. Vaseline will eat some rubbers. Better would be to use silicone.
Vaseline being pure petroleum jelly, it would seem strange if gaskets and O rings made for a filter of petroleum products (Diesel fuel in this instance) would not be petroleum product resistant.
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Old 05-08-2019, 13:55   #15
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Re: Air in fuel system

A very light coating of grease would be my choice, not silicone.
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