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More on Using Car Gas - caution indicated

hevansrv7a

hevansrv7a

Well Known Member
I am doing my 2nd (annual) condition inspection. The gaskets which seal the float sender plate to the tank inboard side are leaking. Tightening them did not help so I will replace them. They were OK at one year.

In order to replace them I had to drain the tank. I removed the fuel drain (CAV-110) to do it. I noted the drain's O-ring is deteriorating badly. Well at least that explains all those little black spots in my fuel samples.

Van's catalog identified the valve. But Van's says to replace the valve if it leaks. Spruce sells the O-rings. It's the -006 size. It also says it is not resistant to automotive fuels. My valves were not leaking yet, but the rings are in in terrible shape and must be replaced.
link to Spruce page

Now I'm wondering if the rubber gaskets on the fuel senders deteriorated for the same reason and if that reason is using car gas.

I only used maybe 40 gallons of car gas during my Phase One and never without it being mixed with avgas. If this is happening because of that, then the severity is surprising. I don't know if back then they were putting ethanol in our premium gas in Michigan (they are now) so I don't know if ethanol is a factor or not.

For you experts out there: what about car gas besides ethanol would damage the rubbery stuff?
 
What else would damage the rubbery stuff in your fuel system? I would imagine the pleathor of additives could cause some damage. I have been an avid supporter of car gas in rv's on this site, but the amount of leaks I have in my tanks now, it's looking like I'll have to start over with new tanks. Not to mention my mechanical fuel pump needs to be replaced. Nothing worse than crusing along and see your fuel pressure drop to 0 and jump back up... and upon shut down, finding gas dripping off the back of a wing.
No more for me, I can deal with fouled plugs and $6 gas.
 
How many hours?

How many hours do you have on your RV?

I have 220 hrs. on my RV7A. I use 100LL in the RH tank for take off's and landings. I use High octane ethanol free unleaded in my LH tank for cruise. I did not use the cork gaskets. So far I have not had any leaks. When I first started flying I did have to replace my drain o-rings because they were deteriorated from sit around for the 4 years while building.
 
Hours vs. Months

I have about 170 hours. However, in this case, I think that the number of months with fuel in the tank is a better indicator. As you can tell, I'm at 24 months. I had my QB wings and therefore the drain fittings, for three years before flight so that's five years for the rubbery stuff, but only two with fuel. I don't really know what's causing the problem(s).

When I re-did my fuel pickups per the SB I eliminated the cork, went with proseal per instructions. This is only about rubber stuff and only the smaller opening for the fuel quantity sender, not the larger opening that's prosealed.
 
bhester said:
I have 220 hrs. on my RV7A. I use 100LL in the RH tank for take off's and landings. I use High octane ethanol free unleaded in my LH tank for cruise. I did not use the cork gaskets. So far I have not had any leaks. When I first started flying I did have to replace my drain o-rings because they were deteriorated from sit around for the 4 years while building.
Click to expand...
EtOH free mogas is the key. No clue if it EtOH caused or contributed to the leaks, but in general, EtOH is not good for things like rubber gaskets.

TODR
 
hevansrv7a said:
I am doing my 2nd (annual) condition inspection. The gaskets which seal the float sender plate to the tank inboard side are leaking. Tightening them did not help so I will replace them. They were OK at one year.

In order to replace them I had to drain the tank. I removed the fuel drain (CAV-110) to do it. I noted the drain's O-ring is deteriorating badly. Well at least that explains all those little black spots in my fuel samples.

Van's catalog identified the valve. But Van's says to replace the valve if it leaks. Spruce sells the O-rings. It's the -006 size. It also says it is not resistant to automotive fuels. My valves were not leaking yet, but the rings are in in terrible shape and must be replaced.
link to Spruce page

Now I'm wondering if the rubber gaskets on the fuel senders deteriorated for the same reason and if that reason is using car gas.

I only used maybe 40 gallons of car gas during my Phase One and never without it being mixed with avgas. If this is happening because of that, then the severity is surprising. I don't know if back then they were putting ethanol in our premium gas in Michigan (they are now) so I don't know if ethanol is a factor or not.

For you experts out there: what about car gas besides ethanol would damage the rubbery stuff?
Click to expand...

The octane boosters in unleaded fuel attack Nitrile O-rings. The O-rings stiffen and shrink. Switch to Viton O-rings as replacements and you won't have any more problems. Here are a few sources for Viton O-rings.

http://www.allorings.com/

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1797452&PMT4NO=49862416

1201T16 is the part number for #006 Viton O-rings in McMaster-Carr's catalog. Price is $4.82 for a pack of 50

You should also check the O-rings in all other parts of your fuel system, as well. Vans fuel injection fuel filter is actually made by a company called Flow Ezy. It's their model 6 ILA that Vans sells. If your 6 ILA filter has brown or Green O-rings, you have the Viton units. If the O-rings are black, you have the older Nitrile O-rings. See

http://198.170.245.162/flowezypagehydraulicfilters.html#HIGHPRESSUREIN-LINEFILTER (Look for High Pressure In Line filters on the page)

http://198.170.245.162/HPInlineFilterpricing.html

http://198.170.245.162/hiPressInlineTechSpecs.html

Charlie Kuss
 
I had a recent experience with the rubber gaskets on the fuel senders too. I could not figure out why I was getting fuel stain streaks under my wing roots but no drips on hangar floor. Turns out that fuel vents at speed add one inch of pressure to tanks and that is enough to cause fuel to seep past the rubber gaskets. Talked to Van's... "We don't use the rubber gaskets anymore, and suggest removing same and proseal." I did this and problem went away. A nasty job, BTW.

Jerry
 
Last edited:
Here's what I did...

I run MoGas in my Subaru powered 7A, and so does a student of mine who has a Rotax powered Zenair 601XL. Both of us had leaking sumps, so I got the following O-rings from McMaster Carr (item number: 8333T116)

MIL-Spec Fluorosilicone O-Ring AS568A Dash Number 006
In stock at $1.61 per Pack
This product is sold in Packs of 5

I replaced the rings a couple of months ago and neither of us have seen a drip since.
 
Cool

Since my Lycoming clone is being fed 10% etoh mogas as we speak!

Cheers I'll order some.

Frank
 
Viton "poor" for Alcohol

According to McMaster's, viton is "poor" for alcohol, though good for gasoline.
 
ethanol

I've used car gas (most of it with ethanol) in my VariEze for eight years. So far, I've had to replace the swollen rubber gascolator gasket twice. Overhauled the carb once because it was so gummed up it wouldn't run unless it was "throttle primed". Three stuck exhaust valves - okay, its a continental. I've always maintained that gas is really not the expensive part of flying. Do the math. Hangar rental, personal property taxes, insurance, maintenance, tie down fees, bi-annuals, medical fees, Jeppeson updates, Garmin updates, AOPA, charts, etc. etc. So why do I still use car gas? Why am I building ANOTHER airplane?
 
Fuel Sender Gasket Which Leaked - Picture

This is the worse one; I haven't removed the other yet. The tears are surprising. I have a dim memory of needing to stretch the rubber to get it to fit when I assembled them 2-3 years ago. The new ones fit perfectly. The rubber is compressed but not deteriorated so my suspicions about auto gas are on the back burner.

I don't want to proseal it because I assume the unit will someday fail and need to be replaced.

Does anyone know which if any RTV is OK with avgas? That would help with the screw holes, etc.
FuelSenderGasket.jpg


FuelSenderGasket.jpg
 
hevansrv7a said:
...I don't want to proseal it because I assume the unit will someday fail and need to be replaced...
Click to expand...
Please don't dismiss proseal type sealant out-of-hand. My own experience, along with many others, is that sealant is much more reliable than a gasket and does not make the plates difficult to remove.
 
Are you guys putting proseal on the rubber/cork gaskets ...or just proseal without the gaskets. I'm working on my tanks right now.
 
N282S said:
I've used car gas (most of it with ethanol) in my VariEze for eight years. So far, I've had to replace the swollen rubber gascolator gasket twice. Overhauled the carb once because it was so gummed up it wouldn't run unless it was "throttle primed". Three stuck exhaust valves - okay, its a continental. I've always maintained that gas is really not the expensive part of flying. Do the math. Hangar rental, personal property taxes, insurance, maintenance, tie down fees, bi-annuals, medical fees, Jeppeson updates, Garmin updates, AOPA, charts, etc. etc. So why do I still use car gas? Why am I building ANOTHER airplane?
Click to expand...

Stuck exhaust valves on Mogas? eh?..how does one explain this? Sure 100ll sticks valves but I assumed that was due to the lead coming out of solution.

Were you using old gas, not flying very much??

Frank mogas for 300 hours and now featuring 10% ETOH
 
hevansrv7a said:
snipped

Does anyone know which if any RTV is OK with avgas? That would help with the screw holes, etc.
snipped
Click to expand...

Thanks for the heads up about Viton and alcohol. Don't use RTV with any sort of gasoline. Gasoline will soften and slowly eat away at RTV. Check the Matronics RV List archives on this. Several listers had used RTV on carb float gaskets to avoid buying a new gasket. The RTV ended up getting caught in the needle/seat area, flooding the carb. Several engine stoppages were caused by this. I've used gasoline to clean RTV off of automobile valve covers for 30 years.
Charlie Kuss
 
Permatex Product, Viton more data

chaskuss said:
Thanks for the heads up about Viton and alcohol. Don't use RTV with any sort of gasoline. Gasoline will soften and slowly eat away at RTV. Check the Matronics RV List archives on this. Several listers had used RTV on carb float gaskets to avoid buying a new gasket. The RTV ended up getting caught in the needle/seat area, flooding the carb. Several engine stoppages were caused by this. I've used gasoline to clean RTV off of automobile valve covers for 30 years.
Charlie Kuss
Click to expand...

I queried the Permatex site and found 80018, 17 or 19 "Aviation" Gasket Sealant and used it to better seal the (new) rubber to the aluminum and most importantly to seal around the threads on the screws. It is quite resistant to gasoline.
link

I bought some viton o-rings locally and their reference said OK for gasohol and auto gas. I won't be using any mogas anyhow because Superior says it is a no-no and the FI pump is an unknown.
 
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