MoGas Thoughts

[juredd1]

I don't mean to start a big issue with this question but I'm at a bit of a loss on this one.

I ran very little MoGas in my 152 as it did not have the STC, so I only ran it when I was out of options. However with the 170 that I recently purchased has the STC and the owner stated that he regularly used some blend of MoGas and and AvGas. The 4 days that I was there there was not set mixture being used by him. He just stated that it has no problems with MoGAS. Sounded good to me as I am 35+ miles from the nearest FBO by car and 35-40 minutes round trip travel time by plane.

So it's much better to drive 6 miles to get 91 octane ethanol free MoGas.

So to my question. After getting the plane home the fuel gauges showed at the top of the red no take off zone, this was AvGas. Not sure how much fuel that means was in the tank but I went and bought two new 5Gal fuel jugs. Went to the local gas station that my Uncle has used for many years to fill up his Aeronca Champ without complaint. Except he uses the 87 octane with ethanol and I bought the ethanol free 91 octane. To be clear I think his tank hold 11 gallons and he burns that up pretty much weekly so it don't set long.

So I poured in the 10 gallons using a Mr. Funnel (Supposed to remove any water in the fuel) and sumped the tanks and it looked strange. The fuel looked really dirty, it was very brown looking as it came out of the tank. I did look at the MoGas that was left in the bottom of the filter and it looked good, color wise. Somewhat confused but just figured it was the AvGas/MoGas mix or something. Even though when I sumped some out of the drain (Sorry guys don't know what it's called) down under the plane (which still had straight AvGas) into the same container the dirty fuel was heavier as it settled to the bottom. Again I was at a loss but was maybe just to stupid but the plane fired up and went through taxi and run up so I didn't think anything else about it. I went flying and had no issues during flight. It was about 4 weeks before I was able to go flying again and purchased another 10 gallons of the 91 octane from the same location. I put 5 more gallon in through the same Mr. Funnel. I had forgotten about the dirty looking fuel until I sumped the tanks again. It didn't add up as I know the fuel I dumped out of the bottom of the funnel looked good yet again. So I poured some of the remaining MoGas from the jug into the same container and it was clear and separated from what I had just sumped from the fuel tanks. I decided to sump the tanks for a bit to see how long that dirty would run out. I probably filled up a 16 ounce bottle from both sides combined before it came out clear. Also the drain down low cleared up really fast and the fuel that I could see through the glass looked good, it was not dirty. I hope I have explained this where it makes sense. Wanted to include everything I done. We also poured some of the dirty part out on a piece of wood and it burned without issue.

Thoughts?

I also tried to add a picture but after 6 attempts at cropping to get it within size limit and some pixel limit I gave up, I am not a well versed photo editor. That would have given you a better idea of the issue.


Thanks,
Justin

[bagarre]

How quickly did the 'dirty' portion separate from the clean fuel?
I'm wondering if it's dirty water that you sumped out.

[Bruce Fenstermacher]

The dirty stuff you got out of the tank was water. That is why it wouldn't mix with the fuel. You will not be able to separate 100LL from MOGAS but water won't mix (at least for long) with either.

Theoretically the top of the red area is a bit over 5 gallons. or a quarter of the 21 gallon tank. And another thing you should know. The red area on the gauge that says no take off is not for the 170. You will not find that marking in the TCDS though most gauges you see have it. My first 170 had one gauge with it and one without.

[C170U2]

Sounds like water. I would recommend shaking the plane from the wing tip until you are sure you have no more water in. I thought I had it all out of mine but was wrong. Shake, sump, shake, sump until it drains clear.

[hilltop170]

Justin-
You live in Arkansas, it is damp and humid and the temp varies a lot. Your tanks are aluminum. If they are left empty for any length of time they will collect condensation inside the tanks with each heat/cool cycle of the atmosphere. That water may have been collecting for awhile and your closer scrutiny using the mogas may be why you caught it. I don't know, I wasn't there, but if it was me, I would always leave the tanks completely full of gas to eliminate the possibility of condensation. It's just as easy to leave it full as empty. Buy some more cans and fill the tanks when you land. You fly often enough that it won't go bad.

To do it right, go to The Chinese Tool Store and buy a real 50-100gal tank for your pickup with a real pump and real particle and go-no-go water filters. Then you can use mogas with more confidence. I would be more worried about burning my plane and hangar down by pouring gas from plastic cans than I would be about the mogas itself.

I used to live next door to the actual Mr. Funnel and have several of them. I have never seen one fail to work. But to increase your confidence, buy a real Chamois skin and bungee cord it loosely across the mouth of the Mr. Funnel as an initial filter and then pour the gas into the Chamois/Mr. Funnel. Any water will bead up in the Chamois and not pass thru but the gas will run right thru. It is also a very good particle filter.

100LL has 4 times as much TEL as the 80/87 used to have. So if you mix your fuel 3:1, mogas:100LL, it will be close to what the engine was certified with.

[hilltop170]

Hi Richard, Justin is having the fuel contamination issue...not me! Thankfully, I've never had a drop of water come out of my tanks.

I drifted off topic and hijacked the thread with the fuel gauge discussion. Sorry!

OOPS! Sorry, missed that.

So Justin, my prior comment is for you, it has been corrected!

[juredd1]

Sorry for the delay in responding, last night was my commute home from out of town work so didn't get back to a computer after my post.

Thanks for all the comments guys. You may be right but it just don't add up in my head. From the time I was in Idaho training and left Idaho heading back I purchased 6 to 7 AvGas fill ups and I never got any of the dark liquid out. Not once. I put two 5 gallon jugs of MoGas in the plane using the Mr. Funnel with and suddenly this appeared. I don't think I am crazy enough to not have noticed it on all the other AvGas fill ups. It's not your normal water color that I have gotten in the past. I've never sumped water of this color out before. I also understand water can get dirty and vary in color. Just scratching my head on where I got it or if it has always been there and why I didn't see any the other times. If it was in my first two jugs of MoGas then my Mr. Funnel did not work.

Finally figured out how to get the picture within legal limits. It should be attached.

[juredd1]

Thanks Richard,

I did not see your post before sending my last one. Well seen it but it wasn't addressed to me.

I do have a couple 50-100 fuel tanks that I tried to use with the AvGas when I had the 152 but it just got to the point where it was to difficult to make it to the airport (35 miles) when I needed it and it was a special trip as I don't work that direction so I decided I'd just rather fly it out there when needed. I bought a manual fuel pump from Tractor Supply to pump it to the plane with but the manufacturer of the pump said that AvGas would eat up the gaskets and they would not stand behind it. I thought they were crazy and bought it anyway. It did not last long before it quit working. So I hope to get those tanks setup with MoGas soon, with a new pump of course.

I've only had the plane here in Arkansas for about 6 weeks before that it was in Idaho. So I would hope the half empty tanks would not gather that much condensation in a weeks time between my arrival and my first 2 jugs of MoGas. I didn't sump before so can't be sure when it got there.

Justin

[bagarre]

Yup, that's water alright. Pretty dirty water at that.

You probably shook things up in the airplane enough to dislodge the water from some place that it was sitting. Now its settled to where you were getting it in the sump.

Probably has nothing to do with your MoGas usage.

But there may me more lurking in your tanks. If I were you, I'd drain and flush the entire system all the way up to the carburetor to make sure you got rid of it all before flying again.

[juredd1]

Fuel Flush.....

I have this sickening feeling of what the heck have I gotten myself into with this plane.....I know it's only water but I do not consider myself a lucky guy when it comes to problems. This comes from a guy that had a bird strike that cost $3k+, cracked cylinder, and a broken value spring within the first 20 hours of flight training in my 152.

So can I perform the fuel system flush or do I need my mechanic to perform this? I don't supposed someone has a whitepaper on this do they?

Justin

[bagarre]

It's not complicated but I think you need a mechanic to pull the screen in the carburetor, clean out the gascolator and the plug on the bottom of the shut-off valve. Most of that should be done at annual anyway.

You're looking at a few hours work, no big deal.

Drain the tanks, open up and clean the screens, slosh around a few gallons of gas in the tanks to make sure everything is out. Grab a nright light and mirror to peek around in the empty tanks..., run clean gas thru the whole system and close it all up.

When I had to drain my tanks (split fuel line) I pull the drain sumps off the tanks and found all kinds of dead critters in there.

[GAHorn]

The problem I have with the "it's water" comments is your statement:

I.... We also poured some of the dirty part out on a piece of wood and it burned without issue....

I wonder if what you have is contaminated diesel fuel. (I'd make a sarcastic MMO joke right now, but I realize you're serious about wanting to resolve this issue.)

Here's another reason not to burn Mogas, IMO. I've told this story before... A buddy in Dallas had a straight-tail 182 and he was an A&P/IA, and he had dedicated mogas setup in the bed of his pickup which consisted of dedicated tanks and pumps to obtain mogas from the local gas stations and take it to his 182. He burned mogas exclusively except when on long cross-country's.
One evening, with a full tank of mogas, we took off at Dallas Love field...got about 500' in the air and lost power. We managed to land straight ahead and towed into the ramp. We drained several gallons of water from his tanks...so much, that we had to dispose of the entire load of fuel. (DAL airport authorities would have been horrified to have seen him drain it down the public drainage system.)

I came to the conclusions that: 1- the local mogas retailers never drain their underground storage tanks, 2- that his pickup truck tankage also condenses water each day/night cycle, 3- that water will rust fuel system components, and that 4- mogas is not for aviation use.

I have had several questionable events using mogas...fortunately non of them fatal...but all of them troublesome, expensive (dump 40 gals of mogas down the sewer and figure how much money you saved ...provided you also didn't lose the airplane or your health), and caused damage to the aircraft fuel system which cost ever more money.

I have never...I mean never...had a single problem using avgas. Ain't that amazing.

In accordance with Richards suggestion, here's the info from another thread:

The quantity of lead in 100LL can be as much as two GRAMS of lead per gallon. That doesn't mean thats what it has, however.
Avgas contains bromides to help scavenge the lead, and if the combutions temps are kept up above approx 1000-degrees it will keep lead deposits to a minimum. TCP also requires high combustion temps to be effective.

Here is an interesting read on the matter: http://www.shell.com/global/products-se ... avgas.html

And, from BP (excerpted):
Manufacture
Gasoline is manufactured from crude oil using various refinery processes to improve the quality and volume of fuel produced. Typically, a refinery will have a number of processes to make components which are then "blended" to give a fuel of suitable quality for the market.
Mogas is manufactured using many different refinery components to meet the demands of high volume production. Components often include reformate and alkylate, high octane materials, cracked spirit - an olefinic material - possibly oxygenated materials such as ethers (e.g. methyl tertiary butyl ether), alcohols (e.g. ethanol) and a host of other possibilities. If some of these components were used for AVGAS there could be disastrous consequences as discussed below.
AVGAS can only be made from a limited set of components of the highest quality. The octane and volatility requirements generally limit the choice of alkylate, isomerate and possibly reformate. As a result, only a limited number of the world's refineries have the capability to manufacture AVGAS. No ethers or alcohols are allowed in the blend as these have a low energy content and would reduce the range of aircraft. This is also captured in a minimum energy specification for AVGAS - there is no such specification for Mogas. ...
Volatility
A gasoline engine requires a fuel which is sufficiently volatile to allow easy formation of the air and fuel vapor mixture required for combustion, while not being so volatile as to cause bubbles of vapor in the fuel lines ("vapor lock") resulting in fuel starvation. Specifications are set to control these properties based on the fuel's vapor pressure and distillation characteristics. These are different for Mogas and AVGAS.

Mogas volatility is set to meet the requirements of ground based vehicle operation for particular regions and seasonal conditions. AVGAS volatility must meet far more stringent criteria for aviation use as atmospheric pressure and temperature can change dramatically during normal operations. For example, fuel warmed to 70° F on an airfield can, in a matter of minutes, experience a pressure drop of 17% as an aircraft climbs to 5,000 feet. The fuel must not cause vapor lock. Similarly, an aircraft descending from 10,000 feet to sea level can experience an almost 36° F swing in temperature. The cold fuel must still be sufficiently volatile as atmospheric pressure increases.
To meet these demanding criteria, AVGAS distillation and vapor pressure are tightly controlled. The result is a fuel which can perform in many different and severe conditions from the equator to the arctic, from sea level to many thousands feet.

After manufacture, small amounts of approved ethers and alcohols may be added as fuel system anti-icing additives. However, this is strictly controlled to meet particular operational requirements. High concentration of alcohols can attack fuel system components and cause seal swelling/failure. They can entrain water into the fuel and promote phase separation into water + alcohol/fuel phases, which may cause engine failure. AVGAS specifications help protect the aviator from these hazards.
AVGAS, and other aviation fuels, are very carefully controlled at the refinery and in the distribution system to ensure no contamination by other products. Red, green and blue dye, respectively, are added to distinguish between AVGAS 80, 100 and 100LL for instance. Quality control follows every batch ensuring it is clean and on specification, ready for use. Overall, AVGAS is the highest quality gasoline a refinery can manufacture...

Many different specifications exist for Mogas across the globe to meet different climatic, environmental and economic requirements. Similarly to AVGAS, the specifications are agreed between the industry members. The aviation industry has no influence over these specifications, while the automotive industry has no influence over AVGAS specifications. ...
Detergent Additives and Gum
Detergent additives are now widely used in Mogas to improve engine cleanliness by reducing soot built-up on valves and injectors. These additives are not present in AVGAS because it contains additives which have been approved for aviation use and are listed in the specification.
Any new additive for AVGAS must be stringently tested to ensure a safe and satisfactory performance.
The detergent additives in Mogas have not been approved in aviation fuels/engines which operate under different conditions to ground based vehicles.
In addition, AVGAS must pass a severe storage stability test to ensure that prolonged airfield/aircraft storage does not result in excessive gum deposits which may block fuel lines and filters. High levels of gum are often linked to the detergent additives and cracked spirit used in Mogas....

[bagarre]

The problem I have with the "it's water" comments is your statement:

I.... We also poured some of the dirty part out on a piece of wood and it burned without issue....

[/quote]

I missed that statement completely. Water wouldn't do that

[blueldr]

I am always amazed at the problems everyone else has had with the use of mogas in airplanes. You'd think with my obvious luck in using it for lo these many, many, years, I should spend a lot more time at the crap tables in Reno.

[hilltop170]

Dick-
It's probably that extra special mogas you guys out there in California get that us poor suckers in the rest of the country can't get our hands on. Maybe they use George Dickel for the alcohol!

I never had any problem with the thousands of gallons of leaded regular mogas I have used either, never heard of anyone having problems with it. All the problems I've heard about was with unleaded with alcohol.