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Another red cube leak

RV10Rob

RV10Rob

Well Known Member
I thought I smelled a faint fuel smell a couple times recently on takeoff and landing. I'm paranoid about fuel leaks, so thought I was crazy, but decided to open up the tunnel, and sure enough, I have a very small leak at the NPT threads on the "red cube" fuel flow sender, as has been reported by others previously. I know this is a recent occurrence, at 147 hours. I'm curious how often this is happening to others. I'd used fuel lube on it before tightening. What have others used?

Incidentally, I think every tapered thread fitting in a high-pressure application on the airplane has leaked: oil cooler, brakes, and now this. Haven't had any other leaks on the airplane.

Just another reminder to be vigilant. I don't get to fly for a month anyway, as I just dropped it off for paint at 52F this morning!

-Rob
 
I had the same problem ...

The inlet side of my red cube would not seal tight with fuel lube, even at ugly hi torques. I finally pulled it out, cleaned the threads completely, and reinstalled with #2 Perrmatex. That fixed it.
 
Maybe I'm wayyyy out of line--

but is seems that the red cubes could have AN threads with oring boss sealing.
Tom
 
Mine has never leaked a drop.

Used fuel lube on the threads.

The max torque listed in the directions of 25ft lbs won't do it.

While I did not design the thing, I think that torque listed is a hold over from the older Flowscan directions. Exceed at your own risk.

Quote from the factory man:
Mathew Sharp said:
You do NOT want to rigid mount the transducer to the motor (any part) using just a fitting. It is a huge safety issue. The fitting could theoretically fatigue and break. You absolutely need to have flexible line on both sides of the Floscan 201B or the EI FT-60 (that Dynon now utilizes).

After manufacturing/supporting flow instruments for a good number of years we have seen that flow transducers accuracy is typically better when mounted after both fuel pumps. They simply seem to prefer to have fuel pushed through them, not pulled through. The truth of it though is that many installation drawings still read as though we were still using the older Floscan 201 transducers. I have seen installs that mount the transducer between the pumps with claimed success. The Floscan units were much more sensitive in regards to mounting location, angles of fittings in and out, and attitude. Our new design will tolerate a lot more. Frankly we don't care if the thing flows straight up, or if you put 90-degree fittings in and out (FT-60 only) of the transducer. Just don't mount it upside down or flowing sharply downhill.



Hope this helps,

Matt Sharp
Click to expand...
 
ok I'm going to scream. :)

FUEL LUBE IS A LUBRICANT. IT'S NOT A SEALANT.

I can't count the number of times people have wasted their time with fuel lube on threads, but its one of those things that just wont go away.
 
Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob
 
think water pipe...

RV10Rob said:
Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob
Click to expand...

Most all plumbing applications will use some form of teflon tape... don't want tape strings in the fuel system in aviation but there are lots of sealant products with PTFE that are acceptable in fuel systems.
 
RV10Rob said:
Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob
Click to expand...

Yes and typically thread lubricant/pipe dope is used to protect the threads from galling before this seal can be established. It also fills the voids left behind from the fact that the machining process most likely won't result in a perfect match between the fittings.
 
RV10Rob said:
Thanks, guys...

Regarding the fuel lube/sealant issue: aren't tapered pipe threads supposed to seal themselves?

-Rob
Click to expand...

I a perfect world, yes. Read on...

"Pipe dope is a reference to thread lubricants, thread sealing compounds and anaerobic chemical sealant that is used to make a pipe thread joint leak proof and pressure tight. Although common pipe threads are tapered and therefore will achieve an interference fit during proper assembly, machining and finishing variances usually result in a fit that does not result in 100 percent contact between the mating components. The application of pipe dope prior to assembly will fill the minute voids between the threads, thus making the joint pressure tight. Pipe dope also acts as a lubricant and helps prevent seizing of the mating parts, which can later cause difficulty during disassembly."
 
rocketbob said:
ok I'm going to scream. :)

FUEL LUBE IS A LUBRICANT. IT'S NOT A SEALANT.

I can't count the number of times people have wasted their time with fuel lube on threads, but its one of those things that just wont go away.
Click to expand...

Maybe that is because just about every add for this stuff says it is a lubricant/sealant. Also maybe it is because the MSDS also says its intended purpose is as a lubricant/sealant. It might also be because it works pretty good as NPT fitting dope at least it did on my airplane.
 
I firmly believe the threads on some of the red fuel cubes are defective
in that they are not deep enough and therefore prevent a tight seal no matter what your preference for thread sealant may be.
I built 2 airplanes using "Tite Seal" on most pipe thread joints and never had a leak on anything except this time on the red cube.
Permatex will probably make up for that machining discrepancy, but Pro Seal
will put the issue to rest once and for all.
 
I am sure many were like Brantel and myself. It says lubricant/sealant right on the tube. I will never recommend it again and apologize if I did in the past.

I switched over to this...Leak Lock by Highside Chemicals. Works from -200 to +400*F and from deep vacuum to 10,000 psi. Switched after using Fuel Lube on 75% of my npt fittings. Don't feel bad guys, I had to reseal oil cooler and brake master cylinder seeps...SO FAR.
 
Brantel said:
Maybe that is because just about every add for this stuff says it is a lubricant/sealant. Also maybe it is because the MSDS also says its intended purpose is as a lubricant/sealant. It might also be because it works pretty good as NPT fitting dope at least it did on my airplane.
Click to expand...

And maybe it just doesn't work well regardless of what the literature says or one guy's experience building one airplane.
 
rocketbob said:
ok I'm going to scream. :)

FUEL LUBE IS A LUBRICANT. IT'S NOT A SEALANT.

I can't count the number of times people have wasted their time with fuel lube on threads, but its one of those things that just wont go away.
Click to expand...

Thanks Bob,

I too have found, that every time someone has a leaking pipe thread,(BRAKE line, oil line,etc.), and ask them what they used for sealant, they usually say:
FUEL LUBE, or it's worthless alter ego EZ TURN! Might as well call it EZ LEAK!

Oh, by the way, if you did use EZ Turn on your high pressure fittings on your master cylinders, crawl under that panel and put your finger on those threads. Bet ya they come away PINK!

I use Loctite 561 for pipe threads.
 
rocketbob said:
And maybe it just doesn't work well regardless of what the literature says or one guy's experience building one airplane.
Click to expand...

All I was trying to do is give you some ideas on why people continue to use this stuff where they do.

Why do all of you experts turn all of these threads into "manhood" measuring exercises?

I choose not to participate.

Going to the hangar now to throw out my fuel lube.
 
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Brantel said:
All I was trying to do is give you some ideas on why people continue to use this stuff where they do.

Why do all of you experts turn all of these threads into "manhood" measuring exercises?

I choose not to participate.

Going to the hangar now to throw out my fuel lube.
Click to expand...

Maybe if you reread your post, and now this one, could see how someone like me could conclude the same thing.
 
Brantel said:
All I was trying to do is give you some ideas on why people continue to use this stuff where they do.

Why do all of you experts turn all of these threads into "manhood" measuring exercises?

I choose not to participate.

Going to the hangar now to throw out my fuel lube.
Click to expand...

Hey Brian,

I'm sorry if I offended you and I'm sure Bob didn't mean to offend anybody, but the fact is, we try to prevent others from making the same mistakes we have made. Sometimes it is a little frustrating to us, when someone offers up, "I've had good success with"...... or "this is what I did", when their plane has yet to fly, or the brakes have never been used, or the engine has never been started.
I'm slightly agitated because I'm in the middle of re-doing an RV6 panel for a guy, and I looked down at the brake pedals yesterday and guess what I saw!
So, now, not only will the panel redo include a complete re-wire of the aircraft to bring it up to standards, it looks like I'll have to re-work the brake fluid fittings too!
Again Brian, your contributions to this forum have been manifold, and I've always appreciated them!
 
Fuel lube

Bob, Is fuel lube the same as "Tite Seal"? I have used the medium Tite Seal and so far have not had any leaks 480 hours mostly in Florida heat. Thanks Gene
 
jthocker said:
Hey Brian,

I'm sorry if I offended you and I'm sure Bob didn't mean to offend anybody, but the fact is, we try to prevent others from making the same mistakes we have made. Sometimes it is a little frustrating to us, when someone offers up, "I've had good success with"...... or "this is what I did", when their plane has yet to fly, or the brakes have never been used, or the engine has never been started.
I'm slightly agitated because I'm in the middle of re-doing an RV6 panel for a guy, and I looked down at the brake pedals yesterday and guess what I saw!
So, now, not only will the panel redo include a complete re-wire of the aircraft to bring it up to standards, it looks like I'll have to re-work the brake fluid fittings too!
Again Brian, your contributions to this forum have been manifold, and I've always appreciated them!
Click to expand...


No worries Jon or Bob. I understand. Sorry if I came across wrong.

The problem with forums is that so much of the nuances of communication are lost. Leads to a lot of misunderstandings and wrong impressions. I have to constantly remind myself of this.

I will buy you both a cold drink someday.
 
GeneL said:
Bob, Is fuel lube the same as "Tite Seal"? I have used the medium Tite Seal and so far have not had any leaks 480 hours mostly in Florida heat. Thanks Gene
Click to expand...

No Fuel lube/EZ turn is not the same as Tite Seal.
 
Tite Seal

Per Wally at Synergy Air, I used Tite seal on all fuel, oil, and brake line connections. Not a single leak or loose connection after 180+ hours, except for the fittings on the brake master cylinders. Apparently the brake fluid I'm using dissolves the Tite seal and they started to leak after 50-60 hours. Teflon tape, carefully applied to keep off the first couple threads, fixed it - so far.
 
Well, after 1.1 hrs on my now dry oil cooler, the Leak Lock(hvac industry) worked. No EZ Turn existed on the four threads inside oil cooler. Heat/oil washed it away. Fittings now five threads deep.

What is EZ Turn/Fuel Lube/"Anti-Sealant" used for then guys???? I cannot imagine lubricating anything with it, so what good is it other than sticking washers before installing nuts/bolts.

I ask our local A&P what he used... Tite Seal and Teflon Tape. I will only use teflon tape on my hvac condensate drains at indoor coils or home plumbing. Never on my plane as I prefer to keep oil jets and fuel system clear.

Don't ever get tired of telling us newbie pilots/builders the best practice. If we can't handle it by now we should not be flying. When we are planning to hop in that plane, egos need to stay on the ground. Maybe there should be a 'sticky' up on vaf about this sticky stuff to warn all of us. Maybe ACS and the online tool stores should stop selling it.
 
N427EF said:
I firmly believe the threads on some of the red fuel cubes are defective
in that they are not deep enough and therefore prevent a tight seal no matter what your preference for thread sealant may be.
Click to expand...

I have found this to be true as well. I have a 1/4" NPT bottoming tap that I've used to open up the ports on the EI red cubes. I just shoved a small piece of paper towel in the opening to keep the shavings out.
 
Am convinced the Red Cube has bad threads ...

Before a ran-tested my engine for the first time , I found a leak at the AN fitting threads on the inlet side of the red cube. I took it out, removed all the fuel lube, goobered it with Permatex #2 and torqued it aggressively. Leak fixed. After 5 hrs of flying the bird I started to get fuel smell. Found a leak on the outlet side of the red cube ... AN fitting threads again. Did the same to that fitting. Also torqued it way harder than most Al to Al threads. Went for a flight test and still had strong fuel smell. Upon returning to the hangar, found the red cube then leaking at BOTH the inlet and the outlet. Re-did the Permatex treatment on both sides and this time torqued the An fittings beyond anything reasonable or prudent for Al. With a booster pump pressure test, I now see no leaks. Can't fly-test it until next week ... will keep my fingers crossed.
I am 100% convinced the red cube's 1/4" pipe threads are defective. These are the only fuel fittings on my entire A/C that have leaked since first engine run, and they are torqued to a ridiculous level.
 
P/S connections

Wayne Gillispie said:
Well, after 1.1 hrs on my now dry oil cooler, the Leak Lock(hvac industry) worked. No EZ Turn existed on the four threads inside oil cooler. Heat/oil washed it away. Fittings now five threads deep.

What is EZ Turn/Fuel Lube/"Anti-Sealant" used for then guys???? I cannot imagine lubricating anything with it, so what good is it other than sticking washers before installing nuts/bolts.

I ask our local A&P what he used... Tite Seal and Teflon Tape. I will only use teflon tape on my hvac condensate drains at indoor coils or home plumbing. Never on my plane as I prefer to keep oil jets and fuel system clear.

Don't ever get tired of telling us newbie pilots/builders the best practice. If we can't handle it by now we should not be flying. When we are planning to hop in that plane, egos need to stay on the ground. Maybe there should be a 'sticky' up on vaf about this sticky stuff to warn all of us. Maybe ACS and the online tool stores should stop selling it.
Click to expand...

EZ Turn/Fuel Lube works good on p/s connections.
 
The proper thread form should be NPTF (National Pipe Taper Fuel) on both mating parts. If you use a pipe tap it should have the designation NPTF on it.
To acheive proper thread depth tap no deeper than 5 to 7 threads remaining on the tap. or plus or minus one turn with a plug gage.
 
Thanks!

I have been fondling that red cube for a couple of days trying to figure out where it will go and thinking about the NPT seal. Information in this thread has undoubtedly saved me hours of headaches.

It is sad that the threads on such a beautifully made part are not more precise. I agree with Tom, a good straight thread and o-ring seal would be more fitting of such a part.

Happily I passed on the EzTurn and decided for my tried and true Permatex Aviation #3. (also confirmed after some research on VAF)

My donation to VAF saves me lots of time! Thanks VAF!
 
I heard from 9A pal ...

...that the EII people have a "passive recall" (their terminology) on certain serial #s on the red cube. They were non-specific about the basis for said passive recall. I'm willing to bet it's a batch of red cubes with defective threads. The passive recall essentially means they remain passive, while we chase leaks. ( Sorry about the sarcasm there, but I'm hugely irritated by the leakage on that device; it's cost me 6 to 8 hrs flying time) If you call them and you have the right serial #, they will apparently replace your red cube.
Additional info ... I ended up installing the outlet fitting a THIRD time with a hardening thread sealant. That finally cured the incessant leakage. The sealant directions said to wait 48 hrs before subjecting the joint to any pressure ... which I did.
Thank heavens 100LL has blue dye in it. Without the traces of blue on the white engine mount and white cowl, I never would have found the source of the problem.
 
Interesting about the "passive recall". If there's a problem, they should really be proactive about alerting people, since it could be dangerous.

I fixed the leak at the "in" side of the red cube back in October with some Permatex #2, and it's still holding up. I'd planned on fixing the "out" side at annual, which is now, and sure enough it's already leaking. Just did the same Permatex fix on that side, so hopefully I'm done messing with this.

Moral of the story: look for leaks with the red cube, and even though it shouldn't be necessary with a tapered fitting, use a good sealant.

-Rob
 
You guys flying RV-10's need to be super vigilant about leaks in the tunnel area!

Some of you may not remember Todd Sweezey's explosion in the cockpit of his -10 a few years ago. It blew out the windows and the left tank OFF the airplane, which subsequently was destroyed by fire.

Best,
 
Two thumbs up for permatex #2

It is a true and proven sealant


Bird
 
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Fuel Fume Detector

That Fuel Leak I had on my red cube had me concerned enough to
add one of these Fuel Fume Detectors. I have had no leaks or fuel smells
since gooping up both fitting threads with Pro Seal.

IMG_2479.JPG


http://www.westmarine.com/webapp/wc...g&matchtype=&gclid=CLnQtdOcsrYCFSHZQgodIFQAuA
 
Google NPT vs. NPTF

Several posts have ask if tapered NPT threads should seal without a sealant. The answer is not necessarily, as a bit of googling will show. NPT threads require the use of a sealant while NPTF do not. Fuel Lube is not a sealant but it might be a satisfactory lubricant with NPTF threads. With NPT threads, which we usually encounter, I always use a PTFE pipe dope/sealant and to date have never had a leak.
 
Another update: it started leaking again at the end of my big trip (though I wasn?t able to find it until I was home). I don?t know whether I didn?t get the threads clean enough when I reinstalled the fittings with Permatex, but decided given the risk to safety and time/effort to keep messing around with this, I?d just start over. One new fuel sender and two new fittings later, hopefully I?m done.

-Rob
 
The threads on the red cubes are not deep enough. I have a 1/4" NPT tap I use on them which will correct the threads. I have a set of taps for this purpose, ground down NPT taps so they are bottoming taps.
 
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