The International Cessna^® 170 Association

After an hour or so of flying last weekend going up to Lake Superior to join the Super Cub guys for their fall colors tour - sitting at a few thousand feet watching the land slide by - out of nowhere my RPM jumped 50 revs or so. Thought that was funny. Re-set the throttle (vernier throttle). About 5 minutes later it did it again. Humph? Maybe my throttle cable was moving or something loose in the carb? Then the third time it hit and I went DUH! Pulled carb heat and RPM jumped up! Well Goooolly Gomer. I'm convinced it was carb ice. Paid attention the rest of the day (as I should have to begin with). Never had ANY carb ice in the 9 years we've flown this bird.

Always a first and always something to learn......

The 1963 Ford Galaxy Convertable, with a carbureted 352 ci. engine, that I bought new in 1963 when I returned from a tour of duty in Guam is running again in the possession of my daughter, Nancy. The alcohol laced California fuel doesn't seem to bother it. I did have to have a good deal of work done on the gas tank after it had been shut down in storage for about twelve years after my wife died. I readily admit that mogas doesn't hold up for twelve years. You can't begin to immagine how bad the stuff in the gas tank smelled. I did have the carburetor cleaned out, and flushed the fuel lines and pump, since I was a little concerned about running the stuff through the engine, but everything else was ok. I still runs great.

blueldr wrote:........I readily admit that mogas doesn't hold up well for twelve years. You can't begin to immagine how bad the stuff in the gas tank smelled.......

Thank you! Now you're starting to get the drift of what we've been saying!

gahorn wrote:... keep in mind that modern autos have PLASTIC and STAINLESS fuel lines and ethanol-resistant synthetic O-rings, hoses, etc.. Our 60 yr old airplanes still have fuel systems which CORRODE, and natural rubbber/nitrile/buna-N components that degrade in the presence of ethanol.

And the cost of complying with certification rules prevents us from making those same changes...

cessna170bdriver wrote:And the cost of complying with certification rules prevents us from making those same changes...

Not really.

Can you look at a black hose and tell me where I bought it?

Can you tell me if using a stratoflex teflon SS hose rather than a black rubber hose is a minor or major modification?

Most of the problems with changing stuff is caused by the A&P-IAs that do not know the rules.

I had Carb ice this last Sat on the way up to OKC. It acted just like the text book examples. This was the second time I've experienced it since I started flying in 1969. I had added 15 gal of Mo Gas, the non Ethanol type, thinking I was topping off. I ended up topping off with another 5 gal of LL100 in each tank. It was 45 degrees at altitude and there was not a cloud in the sky. I assumed low humidity. After a couple of shots of carb heat I ran it the final 40 min of the flight with partial pull on the Carb heat cable and a little more pull toward lean on the mixture. No further problems. I topped off with 100 LL, picked up my Dad and had an uneventful flight home to TXK. The flight home was later in the afternoon/evening. Landed @ 8:20 P.M. It was even cooler at altitude (higher) on the way home. I think it was the Mo gas causing a cooler vaporization in the carb. 100LL(av gas) has adatives that help keep the heat up during vaporization. My 172 has an STC for Mo gas and I have never had any problems with it during hot summer time. I have been using the Mo Gas as a means of lowering the lead content of my fuel so the 0-300D is not as subject to stick a valve by lead varnish buildup. I have had one EX stuck before the mixing. I have never run it @ 100% Mo Gas. This 7 1/2 gal in each full tank is the highest mixture I've ever run.
I might need to be more careful of the Mo gas mix with 100LL in cool weather with moisture.
BTW: I always check the Mo Gas for Ethanol and water content as I start and finish the fill process.

Sixracer wrote:This 7 1/2 gal in each full tank is the highest mixture I've ever run.
I might need to be more careful of the Mo gas mix with 100LL in cool weather with moisture.
BTW: I always check the Mo Gas for Ethanol and water content as I start and finish the fill process.

I'll beat BL to it and say your problem was the 100LL not the MOGAS.

When I could get it I ran 100% MOGAS. Thousands of pilots have flown thousands of ours of 100% MOGAS. I don't think I had any more carb ice than had I been running 100LL. Here is our problem. We don't all have a parallel life going were we run the other fuel in the same exact conditions. Wouldn't life be easier if we did. We could just check in with the alternate life to see which is working better. You may have gotten the same carb ice regardless of fuel.

I simply used carb heat when I needed it regardless of the fuel on board. When I could run MOGAS I may have gotten carb ice more but that is likely because I logged twice as much time in the air on the cheaper MOGAS. Right now MOGAS (with ethanol) is $3.39 cash around the block from my house. 100LL is $6.29

Now before anyone gets technical and says you need more MOGAS to fly the same time as 100LL because of the difference in BTUs your right. But it is much easier psychologically to buy 20% more MOGAS at 20% less cost so I flew more often.

T. C. Downey wrote:

cessna170bdriver wrote:And the cost of complying with certification rules prevents us from making those same changes...

Not really.

Can you look at a black hose and tell me where I bought it?

Can you tell me if using a stratoflex teflon SS hose rather than a black rubber hose is a minor or major modification?

Most of the problems with changing stuff is caused by the A&P-IAs that do not know the rules.

Where would I go to get a carb overhauled with ethanol resistant soft goods?

I got carb ice while flying thru the Pennsylvania hills yesterday at 2500 RPM. I say "thru" because at our height wasn't exactly "over" the mountains.

OAT was about 45 degrees, due point spread was 1 degree and there was LOTS of visible moisture in the air but I'd never had carb ice while cruising before like that. Finished the rest of the trip with partial heat applied.

Can't blame ethanol for that one

Thats also because modern ethanol mogas is not approved in aircraft, so why modify?
Vicious circle.

Bruce,
I never thought about it, but where I get 100LL at our airport is the far remote above ground tanks. Not the tanks that are in the most populated/active area of the airport. It might have fuel in it that has been there all through the hot summer. How many 100 deg & 90 deg days?? You may be right about the gas. It could have perked off some of the lite ends.... It didn't do anything strange on the way back with the 100LL from KGOK. It is pumped from the small bob truck that has a medium sized tank. I would bet it is fresh fuel. Good comment. I might need to look at changing fuel buying location. Thanks for the change in thought pattern!!!

BTY: 111,400 British Thermal Units of energy per gallon in all octanes automotive fuel

Sixracer wrote:I had Carb ice this last Sat on the way up to OKC. It acted just like the text book examples. This was the second time I've experienced it since I started flying in 1969. I had added 15 gal of Mo Gas, the non Ethanol type, thinking I was topping off. I ended up topping off with another 5 gal of LL100 in each tank. It was 45 degrees at altitude and there was not a cloud in the sky. I assumed low humidity. After a couple of shots of carb heat I ran it the final 40 min of the flight with partial pull on the Carb heat cable and a little more pull toward lean on the mixture. No further problems. I topped off with 100 LL, picked up my Dad and had an uneventful flight home to TXK. The flight home was later in the afternoon/evening. Landed @ 8:20 P.M. It was even cooler at altitude (higher) on the way home. I think it was the Mo gas causing a cooler vaporization in the carb. 100LL(av gas) has adatives that help keep the heat up during vaporization. My 172 has an STC for Mo gas and I have never had any problems with it during hot summer time. I have been using the Mo Gas as a means of lowering the lead content of my fuel so the 0-300D is not as subject to stick a valve by lead varnish buildup. I have had one EX stuck before the mixing. I have never run it @ 100% Mo Gas. This 7 1/2 gal in each full tank is the highest mixture I've ever run.
I might need to be more careful of the Mo gas mix with 100LL in cool weather with moisture.
BTW: I always check the Mo Gas for Ethanol and water content as I start and finish the fill process.

Without reservation, I am confident your carb ice had nothing to do with which fuel you burned.
The lack of clouds in the daytime merely meant higher temperatures allowed more moisture to be held in the atmosphere without clouding-up.....and that moisure condensed due to the evaporating fuel, and subsequently iced up in the throat of the carb.
Later, when it was cooler (and therefore clouds formed) less moisture was held and carb ice did not form due to minor variation from the ideal for forming ice.

I've flown these engines in 170/172 aircraft for 45 years and rarely experienced carb ice in most of them...and frequently experienced it in a couple of them. I think it's highly an individualized-airplane occurance coupled with circumstances favorable for carb ice, and that fuel-choices and/or mixtures of fuel-choices, have no repeatable bearing on the matter. Stay Alert!

As for moderm mogas use: I remain opposed to use of ethanol-laced fuel for legal and maintenance reasons, and opposed to mogas useage unless it meets the STC and is kept clean and fresh when delivered and consumed promptly. No storage for more than a couple weeks.

AvGas has a shelf life of 6-months in aircraft parked indoors, 2 years if circulated (such as in commercial storage tanks in common-use) and can be just fine after years if stored in dry climates (as proven by the number of airplanes stored at Davis-Monthans which 20 years after being parked, flew out usng the same gas with which they flew in.)

I can more easily justify the trouble-free operations of AvGas than I can the accident-rate/maintenance-expenses associated with my personal luck with mogas.

T. C. Downey wrote:

blueldr wrote:George,
Why do you suppose that my use of mogas containing ethanol in my cars, my lawn mower, my Vespa scooter, my two small generators and my airplane, with two different engines and fuel systems, has NEVER given me a moment of trouble or any problems at all? You seem to have had a number of relatively serious problems with it and it's quite understandable that you would not want to have those kinds of things in your airplane. One of us must be doing something different from the other. All I have ever done is pour the stuff in and run it. Some of it is not even a little bit fresh. My generators get almost no use and generally about one test run a year. The fuel in my generator on my travel trailer up in Idaho must be at least three years old and it started on the first pull when checked last July.
Doesn't it strike you that we must be doing something different?

Your lawn equipment, and other small engines do not have type certificates to comply with.

Just read an AvWeb piece on mogas, which I have never given any thought to using, until now. I thought the idea was that mogas is ethanol free. Can you run it with an auto-gas STC?
I'm not itching to burn it, but the savings would be nice, and it's available at KSFM. It's also nice to contemplate the prospect of a replacement for 100LL that actually cost less than avgas. Judging by the posts after the AvWeb piece, I would imagine there is a range of opinion on mogas use among the membership of TIC170A.

Jerry, if you'll perform a "search" for that topic you will find many discussion threads in which it was cussed and discussed.

The problem with most STCs is that the auto fuels specified in the STC are:
1-no longer available
2-not retailed in a verifiable specification
3-not always "fresh"
4-contain additives which violate the original specification.

Having said that....if it's clean, fresh, without ethanol, meets octane requirements, and used promptly...it's only other major drawback is that some of your aircrafts' fuel system components may not tolerate it well. (O-rings, gaskets, seals, etc.. may accelerate deterioration somewhat in presence of the autogas components.)

Aryana wrote: I've pumped about 650 gallons into mine this year for about $3500. Saving $600-700 a year doesn't make it worthwhile for my situation.

IF I could get MOGAS without ethanal and I bought 650 gallons I'd save $1911 at todays price difference. Your either paying a lot for MOGAS or your 100LL is dirt cheap.