I've got a set of Monarch fuel caps I'm planning to install this winter.
Reading through the paperwork, I see Monarch lists a sealant-- Sealpak CS-3330.
The instructions made it very clear that this sealant is optional.
I'm thinking there must be a reason, so I'm kind of inclined to not use it.
Seems like some of these sealants are great....until you need to disassemble things, then they're a huge PITA. I've never had a bladder out, but I'm guessing that since it's rubber it's not the most skookum thing in the world. I'd hate for it to be damaged at removal time when the *optional* sealant I used won't come loose.

Has anyone installed Monarch caps or replaced a bladder without using the sealant?
What are your thoughts on it?

I did install Monarchs with new factory cork gaskets and without the sealant. My thoughts were exactly as yours on the PITA potential. I do now have a very slight fuel smell in the cockpit that I'm chasing. Not sure if the two are connected but not sure they are not.
We have to meet up at PT or AWO one of these days!

I have a set on my 1976 185 with bladder tanks. I opted not to use the sealant. There are some O-rings there that do the job without the need for sealant. I have no leaks. I think that if the plates that screw on top of the bladder were leaking you'd see blue stains around the screws, and I have none.

Oops. Deleted double post.

Don't do It! Send them back and get your money back.

I would go so far as to say those caps are about as safe as the killer caps.

My 182b had the caps when i bought it, I just replaced the LH bladder. There was no sealant on it and i only used the gasket for reassembly - no leaks.

Daryl - Not sure what o-ring you mean? Only o-ring i saw was the one on the screw on cap?


I think the caps are great. There are a few possible issues though. The safety chain. If you pile it up on the edge, the cap can potentially bottom out on the chain before its tight. No big deal. just another 2.5 seconds of due diligence. Also need to watch line guys with large fuel nozzles with the ridge, need to be careful with the flapper. i have also found snow will go under the umbrella right up the the o-ring sealing surface. When pulling off the cap, snow is right at the filler neck edge, hard not to drop some in.

You really have no other options for cap replacement, Cessna's are a fortune and not as good as these.

A gasket instead of an O-ring? OK. My memory let me down.

The Monarchs are a tradeoff. The improved Cessna design is the easiest to fill through. The Monarchs flapper could save your bacon if you forget to put the cap on.

I hadn't noticed Mark's observations on my own, but will be I will be diligent.

Bdiazair wrote:I would go so far as to say those caps are about as safe as the killer caps.

Can you elaborate on why? Most folks seem to like them.
I have the early caps with the flap-jack covers and don't mind them,
but the latches on the covers are goofed up and a PITA.
So I figured I might as well install the Monarchs which came with the airplane when I bought it.

I've installed Monarchs on many Cessnas, no complaints except for the hard to fill comment, that flapper can make it difficult to see fuel level.

I've never used any sealant on the top, just a light coat of DC4 (Dow Corning #4) to make it easier to take apart someday. No reported leaks.

I put the Monarchs on my 1954 180 in about 1990 and used the sealant. About 3 years ago I replaced the right bladder and the cap plate came apart from the bladder just fine. I didn't bother to put sealant on this time and so far so good. I think they're great caps and hold my small Mr Funnel just fine when standing on a step ladder pouring fuel in from my 5 gallon jugs. On my PA 12, I took a plastic Folgers coffee can and cut a hole in the bottom to put the funnel in since it needs something to stabilize it.

Bdiazair wrote:I would go so far as to say those caps are about as safe as the killer caps.

HUH? - Based upon what? How about some supporting reasons? Does this have something to do with the bad batch of o-rings that leaked along time ago? I've had Monarch caps on my wagon for many years without any problems and so have most of my friends on quite a few 180/185/182.

Oh, and definitely no sealant. Dry works just fine. Just make sure everything is clean and tighten screws evenly.

I can, basically they leak. The seals they use in the caps looks like a grommet that really doesn't work at all, it's not even a quad seal. They don't keep the water out, and they will not keep the fuel in. Maybe for a non working airplane in an environment where there isn't a lot of precip they would be ok, but it kind of defeats the purpose of them. Have Any of you guys with them ever pulled the caps to fuel and seen water frozen on top of the flapper valve? Or maybe fueled and have had the fuel leaking out of the cap and off the trailing edge of the wing I have. I wouldn't run them on my plane and that being said, I would not recommend them to a customer. They look cool though

Bdiazair wrote:I can, basically they leak. The seals they use in the caps looks like a grommet that really doesn't work at all, it's not even a quad seal. They don't keep the water out, and they will not keep the fuel in. Maybe for a non working airplane in an environment where there isn't a lot of precip they would be ok, but it kind of defeats the purpose of them. Have Any of you guys with them ever pulled the caps to fuel and seen water frozen on top of the flapper valve? Or maybe fueled and have had the fuel leaking out of the cap and off the trailing edge of the wing I have. I wouldn't run them on my plane and that being said, I would not recommend them to a customer. They look cool though

^^^^^Everything he said. Unfortunately. I don't want to turn this into a bashing thread, but my experience has been VERY poor with three different sets of Monarch caps all installed at the same time. Lots of water in and fuel simply pours out of them if parked on an incline. The manufacturer will not address or even acknowledge the problem I have had. They did send new o-rings but that did not fix the problem. Perhaps with enough feedback we can get this issue resolved.

I have intentionally not mentioned this problem on an Internet forum for lack of wanting to be negative. However, I would want someone to give me an honest pirep on an item that can be a genuine flight hazard. Other than the cap sealing o-ring problem, they are a quality-built item. It's too bad but I cannot recommend them at this time.

How can people be having such disparate experiences with these caps?

Both of Kenmore's 180s have Monarch caps, airframes in excess of 15,000 hours, spend all year outside in Seattle (rain!) yet no water in the tanks ever. In my own 182 I can park a full right hand tank downhill with nary a drop spilled. I do keep the o-rings on the caps lubricated with a very light film of DC4.

Granted my example is just as anecdotal (yet perhaps more specific) as both Bdiazair and north river's example are so what's correct in regard to these caps? How can they be this problematic without more uproar from the aviation public? Many hundreds of aircraft are equipped with these caps yet no ADs are out there.

I want to know why you guys are having such poor luck with these things while most of us seem to be having no trouble with them. This is purely selfish, I don't want mine to start leaking!

Could it be that a batch was made where the threaded plastic part of the cap bottomed out before the gasket that seals the perimeter of the neck makes contact? When I get out to the hangar I'll measure mine for depth that have worked great for over 25 years. My gasket definitely makes contact and seals and it is easy to see in the small gap under the umbrella part of the cap. I did buy mine from Barton who invented the things.

mine work perfect no leaks what so ever

Hotrod, since yours are off would you do something for me? Install the cap and put a big rim glass on the underside of the plate with water and see if it leaks when you turn it upside down. If it does, where?????

This guy has a series of videos with them pouring fuel out.

https://www.youtube.com/channel/UCpBhhk ... jVy96XbvPA

Maybe I'll just replace the latches on my covers.....
don't wanna be doing a buncha this
or this