The International Cessna^® 170 Association

Anyone have any info on whether egt and/or cht will vary depending on use of mogas vs avgas?

Years ago I used to use auto-gas, but have not used it since 1998, and now all our fuel in Oregon is 10% alcohol blended so any STC is voided in Oregon.

Temps I see with avgas are 1300F for cruise, I lean to that at anything over pattern altitude.
Dean

The statute of limitations is past at this point so I hope it's it's ok to tell this story.

In the 1970's I talked with the Westach Instrument company and they told me how to put together a six-position EGT instrument/switch from some of their standard parts so I could monitor all six cylinders on my 170. It was a single EGT guage with a six-position rotary switch and I bought and installed six EGT probes in the same place on each exhaust. It was a wiring nightmare for me not having any previous experience with aircraft wiring but everything worked when the engine started. EGT could be monitored on all six cylinders but only one cylinder at a time as the switch was rotated. This was before any engine monitors were available and I had never seen anything but single cylinder EGTs. It worked very well and when it was removed in 2006, all six probes were still working. It was not STC'd or even field approved. Come to think of it, there wasn't even a logbook entry. That was before I knew any of that was required. I flew out of a small country airport and we didn't worry much about that kind of stuff.

It was also before auto gas STCs were available and I was curious whether auto gas would work in the O-300. I had talked privately to Richard Collins of Flying Magazine after a pilot meeting in Dallas and asked him if he had any experience with auto gas. He told me, "I never said this, but I used it in my Tri-Pacer for years and it works great". Since I admired Richard Collins' writing and thought he probably would not have said what he did if it wasn't true I felt there was not much risk in trying auto gas.

Anyway, long story short, I filled one tank with 80/87 and the other with auto gas and took off on the 80/87 tank. At altitude, I leaned the mixture normally, recorded all six EGTs, then switched to auto gas. Nothing changed, the EGTs did not change, and neither did any other perceivable function of the engine. I then tried both fuels in full throttle climb and again saw no changes. I burned auto gas from then on and never had any problems with it. When unleaded gas came along I got the STC and continued to burn auto gas and never saw any problems.

When I got a C-180, it had the auto gas STC and 80/87 soon went away so I ran the evaluation again in the 180 using 100LL and auto gas. I saw the same results, no change to EGT or CHT using a real six-position engine monitor this time.

I have not used auto gas since 1996 so I do not know what effect ethanol might have on engine parameters. We're told not to burn any kind of gas with alcohol in it by the engine manufacturers. Of course, we were also told for years not to use ANY auto gas by the engine manufacturers before they finally said it was ok. So who do you believe? I would like to see some real world experience from someone who is burning auto gas with ethanol in it.

Richard I want to point out the engine will burn ethaeal just fine if it gets to the engine and is not contaminated with water. That is not the problem with it.

The problem is the effect the ethanal wiil have on rubber parts in the airframe like fuel bladders, fuel lines, o-rings and carb floats. I recently found the fuel line on my weed eater desolved due I'm sure to the ethanal in the fuel. Glad it was not my airplane. The other problem of course with ethanal is the water attraction issue.

Bruce is correct, of course. Ethanol (and all alcohols) is corrosive as well. It will simply EAT UP aluminum such as valves, fittings, tanks, etc.. Storing ethanol laced fuel for more than a few weeks in an aluminum-equipped system will eat up your wallet too. (I made the mistake of leaving some autogas in my garden tiller one season. It destroyed the carburetor.)

Thanks Bruce and George-
I never saw why everyone was so upset about carb and fuel line rubber and seals being damaged by alcohol. It couldn't be too hard to change out elastomers with a compound that alcohol won't eat up. Auto makers did it already why not aviation?

The corrosion thing on the other hand is a killer for alcohol. These planes won't last around any corrosion accelerators and if the corrosion problem isn't solved alcohol won't ever be acceptable.

So it looks like there is a LOT more work to be done before we have any reliable substitute for 100LL. I hope we get one before Big Brother cuts us off.

hilltop170 wrote:Thanks Bruce and George-
I never saw why everyone was so upset about carb and fuel line rubber and seals being damaged by alcohol. It couldn't be too hard to change out elastomers with a compound that alcohol won't eat up. Auto makers did it already why not aviation?.....

Automakers don't have to re-certify such substitutions. Aircraft mfr's do,..... but why would they want to when everyone says alcohol in aircraft is a no-no? ... and everyone knows that aviation fuel contains NO ALCOHOL! ?

The type certificate of our 170's says as one of the FIRST things after the Title, "WARNING: Use of alcohol-based fuels can cause serious performance degradation and fuel system component damage, and is therefore prohibited on Cessna airplanes."


Richard, ... what part of "NO ALCOHOL" don't you understand?

George- It's got nothing to do with understanding NO ALCOHOL. I know what the TCDS says. I know alcohol causes problems the way it is sold today. (I also think it's economically ridiculous and bad for the country in general to mandate alcohol's use but that's another discussion.) I'm not using or advocating anyone else use gas with alcohol in it. The type certificate also says "80 Min. octane aviation gasoline" and I can remember very well back in the 1970's the manufacturers all said the sky would fall if we used auto gas of ANY kind. Then Peterson and EAA both got STCs for auto gas and the sky didn't fall when we used it. One of these days the government is going to say no more 100LL. We know it's just a matter of time before that happens. Then what are we going to use? The problem is still there to solve. What I was trying to get across is that just because auto gas with alcohol in it should not be used today doesn't mean someone won't or can't figure out a way to make it work or find some other substitute fuel, then get approval to use it. If that doesn't happen we'll be out of business. It would really be great if someone could find a way to make fuel work that is already readily available for other purposes and not have to invent a new fuel (read expensive). I would gladly accept using gas with alcohol in it if it worked ok and didn't cause problems. I just hope someone figures it out before we have to park our planes. Wouldn't it be ironic if MMO solved the problems caused by alcohol and they both finally got approved?

My little wink was intended to imply a somewhat joking tone of voice.

If they outlaw 100LL.... then I guess we'll use 82UL. I wish they'd go ahead and take the lead out of 100LL and modify the high hp engines to accept it.

CNG would make a fine fuel and we'd only have to modify the tanks and delivery system, the engines would take it just fine. It could be recovered from cattle, save the ozone layer and Al Gore's reputation all in one swell fwoop.