Fuel

[Thart739@gmail.com]

I just got an stc to run car gas in my 170. The manual says its best to use 80 octaine, and as you all know 100 low lead is the only aircraft fuel option now. I would think that regular non ethanol 87 octaine would be the next best thing? I am getting mixed opinions around the airport. I am a new pilot my dad has never ran car gas in our 170. I decide to ask the 170 gurus what's your thoughts?

[marathonrunner]

I wouldn't recommend it. The fuel now is not the same as in the STC you have. There are several posts on this site about this subject. Bluelder ought to be along soon.

[hilltop170]

If you decide to use ethanol free mogas, to get approximately the same lead content as the old 80/87 avgas had, mix 25% 100LL with 75% mogas. Mogas breaks down much quicker than 100LL so if you are not going to regularly (as in every week) fly the plane, it would not be a good idea to use mogas. If the plane is not going to be used for awhile, leave it full of 100LL.

I have never talked to anyone who has had actual problems using mogas in an airplane these days but I have seen with my own eyes what deposits and gunk will develop in a carburetor by leaving mogas in a lawnmower over a winter. Since I started using 100LL in all my small engines, no more gunk and varnish in the carbs.

I used leaded regular mogas for years with good results and no problems in my C170 and C180 with the STCs from back then, I have not used unleaded mogas ever so no first hand experience myself.

[Bruce Fenstermacher]

First non-ethanol MOGAS today meets a ASTM which is allowed under the STC. So while it is true fuel today is not like that of yesteryear, it is still approved for use. Of course you should make sure the fuel your buying does conform to an approved ASTM

87 octane rated MOGAS is the equivalent of 82 octane aircraft fuel as far as octane rating. Our engines are rated for 80 so anything higher is OK to a point. In other words you do not have to buy 89 or 91 octane MOGAS for your airplane.

What you do not want is ethanol in the gas. And not just because it is not legal. It is because, in my first hand personal experience you will cause more problems for yourself from water the ethanol attracts and the rust water will start in the tanks. There is also a possibility the ethanol will eat into some rubber in the fuel system.

One problem with MOGAS and specially MOGAS today is it does not have the shelf life it once had. Keep it fresh in the plane and if your going to store the plane or the plane just doesn't get used that much 100LL will probably be the better deal.

[marathonrunner]

What you do not want is ethanol in the gas. And not just because it is not legal. It is because, in my first hand personal experience you will cause more problems for yourself from water the ethanol attracts and the rust water will start in the tanks. There is also a possibility the ethanol will eat into some rubber in the fuel system.


Bruce, I have aluminum tanks, hence no rust. I do agree it attracts more water. Jeez I am going to butt out of this gas deal. I guess if you can't afford avgas then there are probably a lot more serious things you cannot afford that may be more critical.

It really is not that much more expensive and especially based on the number of hours we typically fly

[marathonrunner]

K y'all I iz pretty stoopid at math. Butt lez sey avgas is 3bux mo a gallon than avgas. Lez see 8 gallonz a hour timez 3 iz 24 timz 100 aww shucks lex make it 10 gallonz a hour timz 5 bux a gallon differnece to make the math eazy. That iz 50 bux a hour timz 100 flying hours a yar iz 500 bux... whooooeeeee I kin by a bunch of Miller lite for that savings y'all

[marathonrunner]

Oops I got so carried away trying to talk stoopid I really did the math wrong. Seriously lets say two dollars a gallon difference at 8 gallons an hour is 16.00 per hour times 100 is 1600.00 so that is a significant savings but still I don't fly every week and letting it sit is not a good option.

How many guys do fly 100 or more hours a year in their 170's? I do not but wish I did just don't have the time and the weather is not always cooperative

[Bruce Fenstermacher]

Bruce, I have aluminum tanks, hence no rust.

Yes I have aluminum tanks as well. But guess what those AN fittings are as well as the quick drains (which happen to sit in the water a the bottom of the tank) and some parts of the fuel gauge that go into your tank are made of?

Ethanal free gas, that is available from one station that I know of within 100 nautical miles is 33 miles by road from my house and about 45 minutes. The gas averages nearly $2 a gallon less than most 100LL in my normal flying area. Luckily the station is 2 miles from work for now and I try to buy 18 gal at a time and bring it home for the weekend flying. Thats $36 sometimes every weekend I get to fly. It adds up quickly.

[blueldr]

I started using mogas in Alaska in 1949 in my Stinson L-5G with a lycoming O-435-11 engine. I did this because the Air Force Tech Order for that airplane said that when operating with the ground army where avgas was not available, mogas was OK. At that time Alaska was still a territory and the road tax on fuel made mogas cost $.50/gal. 80 octane avgas was $.32/gal. The air force (I was a Master Sergeant stationed at Ladd AFB in Fairbanks) had barrells of gas laying all around and they simply begged to be used by someone. The price was right and I've never looked back. I've used mogas, leaded, unleaded, containing MTBE, and containing ethanol in all kinds of GA airplanes with engines with a compression ratio as high as used in the Continental IO-360 ever since. The only thing I have ever noticed about using it was that I NEVER had to clean a set of spark plugs when using it. I have had it stand idle for up to 6 months without any noticeable degradation. I have vacuum testing equipment to test for vapor pressure to watch for vapor lock at altitude, and to test for per cent of alcohol content. All the fuel I have tested here in California has been below 10%. I have NEVER had any problem of any kind using mogas of any brand in the airplanes I used it in and I've never seen any indications of any difference in any engine that I've worked on.

[spduffee]

I'm sure someone, somewhere has posted this before:
http://pure-gas.org/
A list of ethanol-free gas sources in the US and Canada.

[hilltop170]

One way I use to justify (obviously for comedic purposes only) using 100LL is the fact that since I started flying in 1970. avgas has been getting CHEAPER (percentage-wise) the whole time! When I started flying, mogas was 22.9 cents/gal and 80/87 avgas was 45 cents/gal in Texas, or 96.5% higher, twice as much as mogas.

Now, in Texas, mogas is $3.19/gal and 100LL is $4.30/gal at Grand Prairie Airport between Dallas and Ft. Worth. That is only 34% more than mogas.

So, avgas has gone DOWN 62.5% since 1970! Go fly more, it's a bargain!

[bagarre]

$4.30 a gallon for 100LL????
I'm flying to Texas to fill my plane
We're still at $6.00 a gallon in the People's Republic of Maryaland

[hilltop170]

Another GOOD reason to live in Texas!

[Bruce Fenstermacher]

$4.30 a gallon for 100LL????
I'm flying to Texas to fill my plane
We're still at $6.00 a gallon in the People's Republic of Maryaland

Over $6 here in PA. Wasn't to long ago I was buying MOGAS for $4.30 gal.

You know what we have to do is develop a answer numbering system. That way when someone asks about MOGAS we can just post the answer number.

I could say refer to answer #1. BL would chime in, no the only answer is #2. George (who hasn't joined this party yet), will say the answer is absolutely a big Texan #3. BL would then respond to George with a California rebuttal of answer #2A and so on. We could answer the MOGAS, MMO and perhaps a few other questions in just seconds.

In fact if we were smart we'd strike a deal. The first one of the three of us who comes across a newly asked question should just answer for the other two. You know 2, 1, 3, 2A or 3, 1, 2 and for good measure 2A.

Travis, please don't be upset, it is not anything you asked and I really don't want people to stop asking questions. I'm just pointing out how predictable our answers will be.

[170C]

But Bruce, if we had a program like you are proposing we wouldn't get to hear George's comments about mogas and mmo

I burned a lot of leaded, 80 octane and regular unleaded in my C-90 C-140A with very few issues. I did have to change the needle valve and as I previously mentioned, the primer was more difficult to operate as well as the fuel valve would leak if in the off position (but not in any other position). I burned tons, or is it gallons, of mogas in 888A for ten years with no issues. It did not store as well as 100LL (if left for a lengthy time it smelled pretty bad and would leave a rusty stain on the wing). I don't remember ever finding alcohol in any mogas that i tested. As a matter of fact I got to the point I stopped testing for it After my engine was majored, ECI said use of mogas voided their warranty so I went for quite some time without using any mogas--also they started putting MBT or whatever that junk was in mogas. Since that time I have likely burned only about 60 gallons of non alcohol added mogas. If I was out of gas and the only option was mogas with 10% alcohol I would use it to get to the next location w/ 100LL and be sure I burned all that mogas out. As Richard mentioned mogas here in the greater (100 mile radius of DFW) is running around $3.11-3.19 per gallon and at Granbury GDJ & Cleburne CPT, 100LL is running about $4.42/$4.47/gallon, but get out of this area and it jumps up quite a bit. Some of the "big" airports are up to $7.00 per gallon, but then they don't care to have our type planes there anyway. It's going to be interesting to see what they come up with to replace 100LL.