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strong gas smell with V-Power

P

prkaye

Well Known Member
Today I was at a small airport and at the gas pumps they had both 100LL and V-Power (91 Octane auto gas by shell with no ethanol). I decided to try the V-Power, and i filled my right tank, which only had a small amount of 100LL left in it. It ran fine and i burned through most of it this afternoon, but i immediately got a very strong smell of the gas in the cockpit when i started taxiing with it. It subsided a bit at high power, but when i throttled back for approach it came back strongly again. The V-Power gas is much more smelly than avgas.

I?m now grounding the airplane till I can figure this out. I recently sealed-up the firewall really well, so it?s gotta be coming from somewhere further back. But I?ve never seen a hint of liquid gas in the cockpit, so it?s a bit of a mystery. Is it possible to get a vapourized fuel leak through one of hte fittings in the cockpit which would give the strong smell without leading to pooling liquid gas?

Any suggestions or tips on how to diagnose this would be much appreciated...
 
I hope you find the problem. I have a little of the same problem with autofuel. I am assuming it is in the vent tube fittings. I hate smelling gas in the cockpit. I kind of wish I had installed the Rocket type coil vents. Keep us posted.
 
Check your fuel vents and the plumbing leading to them. Autogas typically has higher vapor pressure than avgas, which might explain an unusual amount of venting from your aircraft. That vapor could be exausting from your fuel vents or from a leak in the fuel vent plumbing in the cabin of your airplane.
 
My Rocket has double loops of tubing leading to a under-the-wing vent. All connections are tight. If I fill the tanks beyond a certain point (about 1 to 1-1/2 inches below the filler neck) I will get a strong odor of avgas in the cockpit when taxiing or after leveling off after climbing. If I fill it full and let it sit in the sun an impressive amount of gas will spurt from the vents. Once a couple of gallons have been burned off both tanks the odor goes away. It's coming from the vents.

On my RV-7A I routed the vent lines as detailed by Vans. Originally the "B" nut on one of the vent fittings (the flared connection in the cockpit from the vent fitting to the vent tube) was loose. This caused quite a odor of gas in the cockpit but never any blue stains. I found this by accident and once I tightened it the odor went away.

Auto gas has a higher vapor pressure combined with a much stronger odor. Any venting of fuel in taxiing or flight will most likely be quite pungent. One thing to check is whether this abates once the fuel level in the tank is lowered.

Mark Olson RV-7A F1-EVO Rocket
 
Auto gas stinks.
Try draining the auto fuel and replacing with 100LL.
Your problem may go away when all of the auto gas is purged from the system.
 
I would bet that detector uses a sensor from figaro sensors. I just checked their data sheets and the lp sensor has no data for gasoline. I would bet that it would sense it, but at a concentration probably higher than the human nose could sense.

bob burns
N82RB
 
Try draining the auto fuel and replacing with 100LL.
Your problem may go away
Click to expand...

That reminds me of the story of the man who went to the doctor and said "my arm hurts when I raise it up" and the doctor replied, "well don't raise it up".

Indeed I don't get the smell with 100LL. But I attribute that to the fact that I just don't smell the 100LL. The autogas has helped me identify a problem that was previously undetectable. Rather than ignore it, I'd like to find and fix it.

The first thing I will check is those vent lines. I have the stainless steel bonaco lines (even for the vent lines), so I doubt the lines themselves are leaking, but maybe it is vapour pressure seeping through the threads of the nuts on the fittings. I could tighten these, and perhaps gob some RTV around the fittings to? The vent lines aren't meant to carry fluid (correct?) so there would be no harm in gobbing RTV over the nuts to help seal them up better?
 
prkaye said:
I could tighten these, and perhaps gob some RTV around the fittings to?
Click to expand...

I wouldn't do that, although it would be a good indicator as to where it is leaking since fuel breaks down RTV. As a general rule of thumb RTV should never be used on anything that ever touches fuel.
 
prkaye said:
I could tighten these, and perhaps gob some RTV around the fittings to? The vent lines aren't meant to carry fluid (correct?) so there would be no harm in gobbing RTV over the nuts to help seal them up better?
Click to expand...

RTV is the wrong thing to use anywhere around gasoline. It softens and expands, making it useless as a sealant and downright dangerous if it gets inside the system. Properly installed, the fittings will seal without "gobbing" anything.

John Clark ATP, CFI

FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
RTV is the wrong thing to use anywhere around gasoline
Click to expand...

Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
 
prkaye said:
Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
Click to expand...
As far as your troubleshooting goes, you might examine the flares on your tube fittings. It is possible you could have a bad flare that is allowing vapor to escape. The fix might involve re-flaring the fitting connections. Of course if your plane is like mine that would mean complete new tubing for sections where you would do this.
 
If you plugged the vent and put some soapy water on the threads wouldn't that show you if they were in fact leaking? Of course, the tank would have to be under a slight amount of positive pressure I would think.
 
prkaye said:
Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
Click to expand...

Phil,

All fuel has an odor. If its there, you have a leak. Whether it comes from mogas or 100LL is not relevant. Find the leak and fix it.

If your non standard vents lines and fittings are not up to the task replace them with what is recommended in the build plan.

No amount of glue or adhesive material is a proper fix for a leaking line or fitting.

Note. The vent system is open to atmospheric pressure, there is no such thing as a "high vapor pressure" causing a leak, that is total nonsense. It is possible you serviced the tank so full, fuel was flowing into the vent line at the filler cap and during taxi and in flight liquid fuel flowed out the vent exit, blew back and that's where you got the fuel fumes in the cabin. Turning final in slight slip or skid could cause this to occur then also. This phenomena has been reported before, I believe with the RV-8.
 
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Phil, if the flare fittings are done properly and are secure, no "gooping" is going to change anything. If everything on your airplane is tight, you may be chasing a ghost. As Mark noted in post #5, fuel vented outside the airplane can cause an odor inside the cockpit. Our little aluminum airplanes are fairly "leaky" when it comes to air, plenty of lap joints and rivet lines to let a little air (and odor) in. With absolutely full tanks my '8' will have a slight smell of 100LL until the tanks are burned down a little. Fill it about an inch down, no smell.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
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smell

I had a similar problem (RV8). The very top screw on the fuel indicator cover for the left fuel tank was seeping gasoline. They were installed properly with proseal, etc., so that was the last place I looked in search of the smell in the cockpit. I finally found it and gave the screw about 1/8 turn. It sealed up and the smell is gone. If you smell gasoline in the cockpit....FIND THE SOURCE!!!!!
 
Yes, of course "find the source", as I indicated in my first post I have grounded the airplane until I sort this out.

If your non standard vents lines and fittings are not up to the task replace them with what is recommended in the build plan.
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All my lines, including the vent lines, are stainless flex lines from Bonaco. These are used on many RVs, and despite being "nonstandard", they are superior (and more expensive) than the rigid aluminum tubing lines recommended in the build plan. Therefore I doubt if the problem is incorrect flaring.

The fact that the smell really seems to come-up mainly at low power settings... is this a clue? Does this suggest it's the vent fittings?
 
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The fuel pumps only pressurize the fuel on their discharge end; there is suction on the entire length of fuel line connected to the input side of the pump. So, if there is a small leak anywhere on the input side, it will not necessarily result in visible leakage . I would second what was said in a previous post: SLIGHTLY pressurize each fuel tank to find any leaks in the system on the input side of the fuel pump. This will also pressurize the input lines where there is normally not any pressure, and force fuel to drip out from any leaks so that they are visible.

You can pressurize the fuel tanks by cutting out the valve from a bicycle innertube along with a small square of the surrounding tube and then taping it down over the tank fill hole. Pump air in by hand slowly, and monitor the pressure using water in clear tubing on the air vents to form a home-made manometer. Dont exceed several inches of water displacement in the tube to avoid over-pressurizing your tanks. When slightly pressurized, check for fuel smell and drips inside the cabin and at the wing root, wherever there are joints in the fuel lines.


erich
 
But if it were an actual leak in the input fuel lines lines, it doesn't make sense (to me) that the odor would get much stronger when I'm throttled BACK at lower power settings. I notice it when I taxi, and then it goes away during cruise but when i throttle back while turning base or final I notice the smell strongly again. It seems to me if there were a leak on the input side, this would lead to an even stronger smell when more fuel is flowing at higher power. What I notice is the exact opposite.

Does anybody have a theory as to what could account for this behaviour? Not being an expert on this, it suggests to me maybe it is indeed somehow related to venting?
 
Use Talc to find leaking fittings

Phil,
Forget the fancy electronic sniffer. Those things suck! Dust each of your fittings with Talc [talcum powder will work] If there is a leak, the Talc will be stained, even if the fuel all evaporates before you can inspect the fittings.
As others have already told you, goop will NOT fix the problem. The seal is made between the flare and the fitting. If you have a leak at a fitting, you must inspect the fitting for imperfections and correct the problem.
The only possible "short cut" fix would be to install special copper washers in the joint. See

https://www.pegasusautoracing.com/productselection.asp?product=3202

Actual cracking of the flare will require that the damaged area be cut off and re-flared. If the Talc test shows no signs of leaking, it's just the stinky Mogas and the vent system.
Charlie
 
fuel odor in cockpit using mogas (no ethanol)

Using mogas may have been coincidental with a fuel odor in my cockpit. Odor seemed to be related to boost pump on. Checked several times inflight boost pump on/off - odor was with boost pump on. On the ground later, no fuel odor; turned boost pump on -> smelled fuel; cowling off, boost pump on; found minute leak at fitting where fuel line comes through firewall and connects into gascolator. I loosened fitting and re-tightened, still very small leak. I then completely removed fitting, slid the ferule (sp) back, and looked for a crack in the fuel line flare - no crack. I re-inserted the fitting and tightened it again; boost pump on - no leaks; pulled and pushed on gascolator to simulate vibration/movement with boost pump on (several times) - no leak.

I've flown the bird three times since the above, no fuel odor, no leaks. Needless to say, I checked all fuel fittings. All fuel fittings had been checked for tightness at condition inspection in May --- one never knows....

I report this here to remind others to not overlook what one's airplane may be trying to tell you.
 
thanks guys, all good suggestions. I will definately inspect the entire system including all lines, fittings, fuelp pump, fuel selector etc using talc and running the fuel pump as suggested.

I will not use any goup.

But nobody has yet offered any theories as to why I experience the smell mainly at low power settings - after startup and taxi, and again when i throttle back for descent / approach. Any ideas on what kind of leak would account for this seemingly backward behaviour (i.e. stronger smell when the system is drawing less fuel)??
 
David-aviator said:
Note. The vent system is open to atmospheric pressure, there is no such thing as a "high vapor pressure" causing a leak, that is total nonsense.
Click to expand...

David,

Your other advice was good, but you're mistaken here. Fuel with a higher vapor pressure (typically autogas) will evaporate faster than lower vapor pressure (avgas) blends. That means more fuel vapor will be exhausted out of the fuel vent over time. That will create a stronger fuel smell.

Is it enough to cause the issue of concern in this thread? I have no idea. But it is a possible cause.
 
prkaye said:
But nobody has yet offered any theories as to why I experience the smell mainly at low power settings - after startup and taxi, and again when i throttle back for descent / approach. Any ideas on what kind of leak would account for this seemingly backward behaviour (i.e. stronger smell when the system is drawing less fuel)??
Click to expand...


Could it be main gear legs fuselage penetrating points? There is a gap there I remember a builder reported strong drafts coming from those wells. I prosealed mine. Could it be a fuel tank drain o-ring not properly set and sipping or vent discharging excess fuel, then airflow from lower power settings picks up those fumes and draws them via wells to the cockpit.

You asked for theories we have them plenty :D
 
then airflow from lower power settings picks up those fumes and draws them via wells to the cockpit
Click to expand...

Interesting - so if the leak came from outside the cockpit, then you're suggesting that maybe only at relatively low speeds is the fuel able to travel to a place where it can get in... i.e. at higher power speeds maybe it just gets blown back out of the way. I'll plug up those gear-leg holes and my (rather large) flap pushrod holes, for good measure.

You asked for theories we have them plenty
Click to expand...

And every theory gives me something else to check. The curious aspect of the smell only at low power settings does seem to me like it should be an important clue. This fact seems incompatible with a typical fuel leak inside the cabin. So any other theories that would be compatible with this clue (smell only at low power settings) will be much appreciated!
 
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Phil:

Are you sure it's low power settings that'st the trigger? The situations you enumerated seem to closely align with times that the boost pump would be running or would have just run.

Also, the times that you listed are when the airplane is slow. Being slower = less air circulating through the cockpit. It could be leaking vapor continuously and you're simply not smelling it when moving fast.

Pull your wing root fairings as well and check your tanks. It doesn't take a lot of fuel leaking in the wing root to get vapors to waft into the cockpit. I know -- been there, done that.
 
Are you sure it's low power settings that'st the trigger? The situations you enumerated seem to closely align with times that the boost pump would be running or would have just run
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Doesn't seem to be correlated to boost pump. I throttled back without putting the boost pump on and got the smell. Could be related to speed, as you suggested.

Will definately remove the wing root fairings and inspect those covers.
 
Kyle Boatright said:
David,

Your other advice was good, but you're mistaken here. Fuel with a higher vapor pressure (typically autogas) will evaporate faster than lower vapor pressure (avgas) blends. That means more fuel vapor will be exhausted out of the fuel vent over time. That will create a stronger fuel smell.

Is it enough to cause the issue of concern in this thread? I have no idea. But it is a possible cause.
Click to expand...

Yea, I know mogas evaporates quicker than 100LL. I was using the stuff a few years back and checked its VP before every flight. It was usually good for about 15,000' vrs over 20,000' for avgas, depending on temperature.

But mogas or any other fuel vapor does not build up pressure in the vent system. I don't see how it could unless the vent exit was blocked.

The way the Vans vent system is designed, a slight pressure build may occur due to ram effect. I get more than a little ram pressure build up because a couple forward facing vent line inlets. That should force any liquid in the lines back into the tank. I think Phil has the same set up. Its a good idea because that little head of pressure gets fuel moving toward the engine better than no ram pressure. But I don't think it will cause a fuel smell in the cabin, at least I've never had it with my beast over a 7+ year relationship.

The fuel vapor smell at lower power could mean vapors are being drive by prop air flow and when there is less of it due to the prop coasting, vapor could be entering the cabin rather than blowing by. The question remains, where are the vapors coming from?
 
prkaye said:
Today I was at a small airport and at the gas pumps they had both 100LL and V-Power (91 Octane auto gas by shell with no ethanol). I decided to try the V-Power, and i filled my right tank.
Click to expand...

91 Octane seems to be a very low octane mogas to use in a Lycoming.
 
Exhaust

I think what you are smelling is just unburned fuel coming out the exhaust.
At low power settings it's running rich and just finding it's way into the cabin.
Try really leaning it at that low power setting and see if it helps.

Mark
 
My Fuel Smell in the Cockpit Experience

Two or three times now I have smell gas fumes in the cockpit, always in cruise with no preceding changes. I have looked at every single cockpit fuel connection with mirrors and magnifying glasses, not a spot of blue anywhere.

Based on my experience I believe it is a vent issue. Reinforcing this theory, it has only happened on hot days. Worth checking every single connection very carefully before you reach this conclusion, however.

I also have a very sensitive schnoz.

Hans
 
Do you get the odor in the cockpit at idle either without moving or during taxi? If so, why not do an experiment and hook up some tubing over the tank vents and run it back to the tail, secured with tape, away from the cabin. then sit at idle and during taxi and see if you still get the odor. No smell would confirm that it is the vents. I'm thinking it's not, but can't rule it out either. Might be worth a try.

Erich
 
Phil,
I can't see on your profile but I'm guessing you might have an O-320 in your RV9A. If it's carbed, you might have a leak in your accelerator pump.
I had this happen on my RV4 many years ago. I would get a strong fuel smell when I throttled back. I only found the leak when I switched to 80 octane. That stuff left visible stains on the firewall and carb area. It was a simple fix, for the old carb I was using. I got an accelerator pump kit, installed it, no more stains, no more smell! Good luck!
 
Never thought of that!

jthocker said:
Phil,
I can't see on your profile but I'm guessing you might have an O-320 in your RV9A. If it's carbed, you might have a leak in your accelerator pump.
I had this happen on my RV4 many years ago. I would get a strong fuel smell when I throttled back. I only found the leak when I switched to 80 octane. That stuff left visible stains on the firewall and carb area. It was a simple fix, for the old carb I was using. I got an accelerator pump kit, installed it, no more stains, no more smell! Good luck!
Click to expand...

Good advice, Mutha.

FWIW, I run MOGAS on occasion in the 550. I get a smell in the cockpit too - but never with 100LL. My suggestion is that there are no leaks; you are smelling vapors - probably coming in thru the flap actuator holes (directly behind the vents - not the best plan) - it could be simply that you (and the rest of us) are used to the 100LL smell, and don't smell it anymore. Ex: I worked in a dairy for a few years (previous life), and I didn't smell anything, but visitors sure did!

I will volunteer that if you don't see any obvious stains, blue or otherwise, you are good to go. Please do check for leaks, tho!

Carry on!
Mark
 
Ok, thanks guys. This gives me lots of things to look for.
Indeed I had wondered whether the smell was coming from the exhaust getting in through either the gear-leg penetration holes or the flap actuator holes. I'll seal both of those up too.

I do have a carb'd O-320. Is the "accelerator pump" the same thing as the cylindrical mechanical fuel pump mounted at the back of my engine? I'll definately check that for leaks...any possibility fuel leak FWF is quite a scary thought to me.

I'm going to plan to spend a day out at the hangar checking all this stuff before I fly again.
 
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Don't confuse the fuel pump with the accelerator pump

prkaye said:
snipped Is the "accelerator pump" the same thing as the cylindrical mechanical fuel pump mounted at the back of my engine? snipped.
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Phil,
NO, the accelerator pump is part of your carburetor. Look carefully at your carb. You will see a round shaft coming out of the body of the carb. There is a seal between that shaft [accelerator pump shaft] and the carb body. This is where a leak could develop.
FYI, I have a video on rebuilding these carbs. Contact me via email [click on my user name, at the top of this post to get that info] if you would like a copy of it.
Charlie
 
leak found

So I spent some time yesterday tracking this down.
With the engine off, I started the boost pump and fairly quickly got a whiff of gas. So I started checking fittings.
I found a leak through the pipe-thread on the elbow fitting that penetrates the firewall into the gascolator. Gas seeped out through the tapered pipe thread when the fuel pump was on (this is the first fitting downstream of the fuel pump, so probably a fair bit of pressure there). I could actually tell that the carpet underneath that fitting had been getting gas on it.
I replaced the elbow and put Loctite 567 Thread Sealant on the threads this time (i had previously just used fuel lube). Waiting a couple of days for the sealant to cure and then I'll pressurize the system and check again.
I HATE TAPERED PIPE THREADS!!!
 
bit of smell in climb now

Ok, well after replacing and sealing that fitting (and sealing my flap rod egress holes) i thought i had the smell gone. Almost. The other day I filled up with V-Power again, and again noticed a smell. I double checked that fitting, which has remained dry.
This time the smell was much less potent (only whiffs really), and after a few hours of flying and experimenting, it seems I only get whiffs of it in a climb. At cruise, no smell - even a high power cruise. This suggests to me that it's aircraft attitude / AOA that determines when I get the whiffs of fuel smell (and only noticeable with auto gas - great way to test!). Does this suggest it is indeed a venting problem at this point? It's hard to diagnose a leaky vent fitting, since there's normally no fluid in it -but I'll unscrew and visually check the nuts and flares anyway.
 
Fuel lube, EZ turn

prkaye said:
So I spent some time yesterday tracking this down.
With the engine off, I started the boost pump and fairly quickly got a whiff of gas. So I started checking fittings.
I found a leak through the pipe-thread on the elbow fitting that penetrates the firewall into the gascolator. Gas seeped out through the tapered pipe thread when the fuel pump was on (this is the first fitting downstream of the fuel pump, so probably a fair bit of pressure there). I could actually tell that the carpet underneath that fitting had been getting gas on it.
I replaced the elbow and put Loctite 567 Thread Sealant on the threads this time (i had previously just used fuel lube). Waiting a couple of days for the sealant to cure and then I'll pressurize the system and check again.
I HATE TAPERED PIPE THREADS!!!
Click to expand...

It's been my experience in the past, that every time I used Fuelube/EZ turn for a thread sealant, that fitting eventually leaked!!!!! I now use anything that says "thread sealant" on the tube for my pipe threads. I think I use loctite 561 with good success.
 
that every time I used Fuelube/EZ turn for a thread sealant, that fitting eventually leaked!
Click to expand...

Ok, yes, this has been extensively discussed earlier in this thread and in many others. As I wrote in my final post on this thread a few weeks ago, I solved the leaky pipe thread problem using Loctite 567.
Today's post is an update and a question - I am now getting only whiffs (only noticeable with auto gas), and I only seem to get the whiffs in a climb (no smell in cruise at any power setting). I suspect that this suggests a venting issue - am looking for validation of this suspicion.
 
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Phil
It is possible, as you suggest, that you are getting vent fumes into the cockpit at climb angles. Is it the same at full fuel vs lower fuel levels?
Also what about directing the vent outlets and away from the cockpit area to test that theory. If you do this you should experiment the technique with one tank first to make sure that the tank is still properly venting.
 
Symptoms are exactly the same as my recent bout with a fuel leak. Fuel smell in the cockpit at low airspeeds and low power settings. I was told that the vent tube is the likely cause...

Turned out to be a fuel leak at the wing root, tank end rib. Wasn't leaking enough to make fuel stains, but at low power settings and low airspeeds the fuel vapor would find it's way into the cockpit. I did finally find some fuel stain near the vent tube fitting on the tank itself reinforcing the false belief that the vent system is at fault. Pressurizing the tank with over half a tank of fuel revealed a leak coming from behind the tank support bracket. I don't know what the tank is pressurized to in flight by the vent system, but it didn't take much for the tank to start leaking on the ground (it wouldn't leak otherwise); really just closing off all the fittings and squeezing the tank by hand was sufficient. Talcum powder is a great idea and wish i'd thought of it when I was trying to find the leak.

I removed and repaired the tank last week. Flew it for the first time since the repair today. No fuel smell. :D
 
See post #31
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Hmmm... what I was trying to explain (unclearly it seems) in my recent update post yesterday is that my symptoms are DIFFERENT now after my fix of the one seeping fitting. Now the smell is much weaker, and it's not low power settings that triggers it now - these new wiffs now seem to occur at low airspeeds. I get them in a climb (at high power), and a little bit when taxiing or idling (low power). In cruise I don't get the whiffs.
Suspecting either venting, or a subtle leak on the inboard end of the fuel tank(s) as in the case of the previous post (although I had the fairings off recently and found no obvious leaks there). In cruise, it seems whatever it is gets blown away unnoticed. The hunt continues. At least now it's only occasional mild whiffs.
 
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