Air leak in fuel system

[Eric Howell]

I DIY installed a an SMX double double with the self priming bulb a year ago. The system is a huge improvement over my old racor set up.

Since install I’ve had a small air leak.
Using clear hose I’ve tracked it down to my primary/SMX (NOT the last chance on engine) fuel filters set up (checked fuel flow from tanks, selector valve, etc and no air). I’ve tried changing the filter canisters, but the leak persists. It’s not horrible, the engine never shuts down, but she does stumble after idling for extended periods as she clears the air. At 1900 RPM I can easily see the pea sized bubbles every few seconds in the clear tube after the fuel leaves the primary filters, vacuum is about 3”.

I did use pipe dope (loctite 567) on the npt barb threads and grease on the filter rubber rings.

Is it possible to over tighten the filter canisters? My rubber filter rings look distorted after removal. Is pressure testing the set up an option?

Sorry the pics aren’t great, but space is tight where the filters are.

Many thanks
Eric

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[Eric Howell]

Rob Schepis wrote:

Surprised the “hired professionals” didn’t propose the option to you…

I gave up on that yard 8-10 years ago. A lot of errors….. not just the decks.
I do a lot of DIY but cutting into pristine decks with a high probability of incorrect location makes me squirm. The yard I use now says they’ll domit when repairs are needed and they’ll make water tight hatches then.

[Rob Schepis]

Surprised the “hired professionals” didn’t propose the option to you….Well if it’s clear deck space with no equipment mounted in the way there’s a few options as to access hatches if the need arises.

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Eric Howell

[Eric Howell]

Rob Schepis wrote:

So you replaced the tanks in ’06. Was a new deck glassed in over the tanks at that time?

Yes, I had a new deck made. Unfortunately I didn’t know enough at the time to ask for access hatches to the fuel pickups and returns. That’s caused me heartache ever since.

[Rob Schepis]

Yes that makes. So you replaced the tanks in ’06. Was a new deck glassed in over the tanks at that time?

[Eric Howell]

Rob Schepis wrote:

I’m confused about access to the top of your tanks — you say there is no access under the solid deck yet you also noted that you ran clear tubing FROM the tank ??

Sorry about that Rob

I have a 2’ clear hose that I connected to the end of the hose that runs from the fuel tank(s) and then connected the other end of the clear hose to the fuel selector valve. Basically patched it in. I can’t access the tank side of the fuel hose, just the fuel selector valve side.

I hope that makes more sense.

[Rob Schepis]

Easy enough to double check the plugs in the unused ports on the backside of the filter heads, can’t hurt..

I’m confused about access to the top of your tanks — you say there is no access under the solid deck yet you also noted that you ran clear tubing FROM the tank ??

[Eric Howell]

TJ wrote:

The reason I ask is I worked on a Tolley craft maybe 12-15 years ago that was a gas to diesel conversion. The pick up tube’s had very small holes drilled about 1.5 in. Down from the top. ( was told they were for anti-siphon reasons on a gas engine. )

Is it possible for you to hook up a deck mounted feed tank maybe 5 gallons for a quick test?(Just be sure not to overflow your onboard tank with the return.)

Thanks TJ. She’s always been diesel, but I did repower her with the 6BTA a dozen years ago. I also had new tanks installed then (‘06). I think your idea about a deck tank is a good one. I have a 5 gal diesel jerrycan I can use.

[TJ]

Always diesel boat ?

The reason I ask is I worked on a Tolley craft maybe 12-15 years ago that was a gas to diesel conversion. The pick up tube’s had very small holes drilled about 1.5 in. Down from the top. ( was told they were for anti-siphon reasons on a gas engine. )

Is it possible for you to hook up a deck mounted feed tank maybe 5 gallons for a quick test?(Just be sure not to overflow your onboard tank with the return.)

[Eric Howell]

Oh wow. That gauge set up looks great. Yes, I can get air to the dock.
I wish I read this before installing the new filters. The schematic on one of the filters showed 3/4 turn, which I could not do even with a wrench. I am going back to the hand tight method you’ve mentioned.

I did vacuum test the filters but I’m not sure it told me anything. I shut off the fuel inlet at the primer bulb and ran the engine until about 7” of vacuum showed on the gauges. I then shut down the engine to see if the 7” would drop. After an hour less than an inch difference (6-7” showed after an hour). I’m just wondering if there’s a leak somewhere other than the filters, earlier in the system and the bubbles are too small to see until they collect in the filters and then come out in globs… if that makes any sense.

I’m worried my pick ups at the tank have an issue, and of course they’re under the solid, no acces, deck.

[Rob Schepis]

Further to my prior post — if you can get pressurized air at the boat you can use something much like what I use for aftercooler pressure test, a Schrader valve and gauge.

[Rob Schepis]

Okay, so all is tight and properly installed with thread sealant.

Back to your original questions:

Distorted filter gaskets upon removal sounds concerning. I have never done anything other than wet the gaskets with fuel and with clean dry hands and a dry filter make the filter HAND TIGHT nothing more, no wrench. Basically as tight as my dry hands will allow without getting red in the face, if that makes sense. Oil or fuel, all filters the same way. Never an issue in decades. Wrench for removal only. Might try cleaning the gaskets and both gasket sealing surfaces and resetting the filters.

Yes you can pressure test the filter assembly, something like 15psi. But you’re not getting serious air so may take quite a bit for it to drop. What will you use – do you have a coolant tested to adapt?

[Eric Howell]

Thank you Rob for the response. I do have thread pipe oozing out of the connections, but not nearly has pretty as yours. I also used sealant on the vac gauges and the bungs for the ports not used by the vac gauges. I don’t see any signs of leakage, but it must be there somewhere.

For testing, I ran the clear tubing between the tank and fuel selector valve (no air), between the fuel selector valve and the primary filters (no air) and the between the primary filters and engine (+ air, pea sized bubbles every few seconds).

I also changed all of the fuel hoses except the tank to the fuel valve (those hoses are under the deck and would require cutting it up to access).

Thanks.

[Rob Schepis]

I downloaded and zoomed in on your photos. I know you said you used the pipe thread sealant but from what I can see in the pics it looks like zero excess was pushed out of the threaded connections. Here’s a recent install I did for comparison using Rectorseal Blu.

Did you have any issues with the orientation of the fittings in that you were stuck as to not being able to get another turn out of it so you backed off leaving a connection a tad looser than you would have liked if orientation was not an issue?

Did you use the sealant on the vac gauge threads?

Any signs of leakage from any connections?

From where to where did you run your tubing as part of your testing?

BTW, I’ve never greased a filter gasket — oil filter gaskets get oil, fuel filter gaskets get fuel.

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