Monarch Fuel Cap Leakage on Cessna 182

Monarch Fuel Cap Leakage on Cessna 182

I have a 78 Cessna 182.  I purchased, about a year ago, two Monarch fuel caps to get rid of my "killer caps".  Both worked fine for a month or two, before they both started leaking.  The manufacturer stated that his caps "release pressure" at a lower pressure than the Cessna Caps, thus I was building up to much pressure...and fuel was allowed to escape when the cap vented.

Thinking it might be a cap defect, the company sent me two new caps...which again worked fine for awhile..then started leaking fuel.

My mechanic believes that the orginal caps, and the mods from Cessna, do not vent out..only in just incase of fuel vent blockage.  Therefore, I am wondering if the problem might be that I have the wrong caps, that vent but do not need to, or if anyone has any other insight as to the problem.

We checked the fuel vent thinking that it might be out of alignment and therefore taking in to much ram air, thus allowing the build up of too much pressure.  It seems to be as the manual dictates.

Does anyone have any insight before I purchase new caps from Cessna to alleviate this problem?  I have already tried switching tanks occasionally to alleviate the pressure and stop the syphoning affect, but this does not work.

Thanks,
Brian Greenlee

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Re: Monarch Fuel Cap Leakage on Cessna 182

Hi, Brian,

I read your email with interest, since I've suspected substantial fuel losses (via vapor, not liquid) since I bought a 182 four years ago.  Problem is, I've not been flying a lot, so my measure of fuel loss over the years has been erratic and not well quantitated.

Have you received any response from other pilots, or from Monarch about this?

Thanks--
Lynn

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Re: Monarch Fuel Cap Leakage on Cessna 182

Lynn:  For what it is worth, I purchased the Monarch caps and riser shields for my 172 several years ago and had the same problem as Brian.  Apparently, the Cessna caps do not vent out at all and they never leaked.  The Monarch caps are evidently designed to vent both ways when pressure is high (or low) enough.  I was getting fuel leaking out especially when when climbing at high angles of attack with full tanks.  After looking at the vent valves in the caps I decided the only way to stop the leakage was to block/modify the vents...  I went back to the stock Cessna caps with no problem.  (I kept the riser shields which cover the depression around the caps to prevent water standing around the caps) 
  I don't know if these vents are the same as the 182 caps but I suspect they are.  I think Monarch is out of business now...
I have not heard of any vapor venting problems, though.

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Re: Monarch Fuel Cap Leakage on Cessna 182

I had the monarchs installed 3 years ago on my 1969 C185 and they worked fine, but in 2008 they started leaking out the top, I replaced one fuel cell but still they leaked out the top, i took off the safety chains from the aps thinking they were vibraing into the flapper and allowing fuel to escape and that worked for a couple of weeks and now i am spewing fule out everytime i fly, last evening over 15 gals in less than 30 minutes,, expensive and wastefull.  Has anyone modified th caps to not vent? if so how to?  Steve

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Re: Monarch Fuel Cap Leakage on Cessna 182

I have a 69, Cessna 185, and am having same issues with the monarch caps (leaking) as many others are. My research makes me think it is the  ratchet assembly that is the problem. I have four caps and by comparing the amount of torque that is required to make the ratchet work it is noticeably different, cap to cap. This means the the seal/o-ring does not make a tight seal. It kind of seals. When I screw the cap in, and the seal just touches,the mating surface, I can only get about 15 or 20 degrees more turn before the ratchet assembly starts to ratchet. That is on the good cap. Sometimes it leaks and sometimes it doesn't. The other caps give me maybe 10 to 15 degrees, and leak more often than not. I have done the under the wing vent tubes and believe that they are within manual spec's. Other forums besides this one, talk of fuel venting out of the cap vent. If you try to blow on the cap to make this over bladder pressure vent relieve, it takes all a person can muster. Most of us can blow about 2 psi and believe at that pressure, and the area of the bladder,things should bend or at least be distorted.  One fellow lost a cap in flight, which seems to me to be quite likely if a person cannot properly tighten said caps. The fact that Monarch thinks it's wise to have an internal flap makes me think they think cap loss likely. I think they need to be recalled! What's worse water in your fuel or no fuel?

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Re: Monarch Fuel Cap Leakage on Cessna 182

I am pretty sure I have fixed my leaky caps. In my last post I said I thought the problem was the ratchet assy's in the caps. They ratchet to soon and therefore a person cannot screw the caps down tight.
I changed all of the o-rings to viton #326 o-rings, and greased them with silicon grease before I installed them. I also checked for and removed any plastic bumps etc. form where the o-rings sit. There seemed to be seams from the manufacturing process that have little ridges that might cause leaking. Then I checked and bent down, out of the way, the clips where the chain attaches inside the filler necks. One of these clips/tabs was scratching the very end of the cap, and stopping it from rotating. Finally I found that if you put pressure on top of the cap as you screw it in you can get the caps down so the metal part of the cap almost touches the skin of the wing. This means that the o-rings are down in the filler necks and not just barely touching them like before. I flew last night and have not streaks.

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Re: Monarch Fuel Cap Leakage on Cessna 182

I just bought a 1969 182 and want to replace the current killer caps, Cessna wants about $1700. and Monarch is about $600.
The cost savings is not worth leaking gas caps.
Any thoughts?

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Re: Monarch Fuel Cap Leakage on Cessna 182

I had the earliest "killer" caps on my 55 180 and replaced them with the Monarchs when I replaced the bladders.  I wish I hadn't.  All the above occurred.  Slight weeping from the cap, at first.  A year later, with fuel selector on Both, there are heavy blue streaks on the wing from the cap back.  If I isolate the underwing vent (left wing only on my bird), it still vents out the Right tank's cap.  The cap check valves appear to work correctly, as described above.  So, it must be the gasket/ratchet issue as John states.  I'll try the #326 vitons.

I wish I could have left my 'killer' caps on.

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Re: Monarch Fuel Cap Leakage on Cessna 182

Hi Ticked
I think we are just stuck with leaky caps. I have found that over time the o rings dry out and then you cannot screw the caps down enough to seal, so I lost fuel again my last flight. I need to grease said o rings before I go again. I would like to modify the ratchet part of the cap but that might void my insurance or something?????. I kick myself for changing too.

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Re: Monarch Fuel Cap Leakage on Cessna 182

I am a newbie pilot and cessna owner but a lifelong mechanic.  I posted earlier on this site about concerns I had regarding the venting system on my 172F. It's a poor design that wouldn't pass muster on your car or even your lawnmower.  Fuel caps wear out and are normally common cheap replacement parts on most equipment. But not on a Cessna. Your car doesn't spew gas when you drive up a mountain and the pressure changes. But not on a Cessna. The EPA wouldn't let your car or lawnmower spew gas all over the environment. But it allows it on a Cessna.  There is much posted about water in fuel problems on high wing planes and much can be laid on this poor venting system. 

As I am not an aviation mechanic or engineer I cannot propose a fix.  But I can certainly say that something needs to be done.  There needs to be a redundant fuel venting system besides the wing tube and cross tank tube.  Some Cessnas have a AD that involves a secondary vent on one of the tanks.  But when the caps are so prohibitively expensive that nobody replaces them, you wonder if that vent valve will work in a crunch.

Many modern engines have fuel systems that internally vent thru the fuel intake systems.  Is that a solution?  Or a vapor canister?

I don't know folks.  But a problem exists and an answer needs to be found.

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Re: Monarch Fuel Cap Leakage on Cessna 182

Thank you for the tip to try the Viton #326 o-rings. I installed the Monarch caps about a year ago and one of them started leaking. I tried the Viton #326 o-ring and solved the problem perfectly.

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