STC for mogas in O-235

Hi everyone. I was reading about Petersen's STC to use mogas in the O-235.
Apparently the STC for the O-235 only allows premium (91 octane) to be used.
I would still be reluctant to use premium since it is a "step down" in
octane for the O-235. I would not have a problem if I was flying an O-200
and could "step up" to 87 octane since the engine was originally certified
to run on less.

Has anyone ever found premium available for aircraft use at an airport? To
tell the truth, I have never flown into an airport with mogas available.
The chance to cut down the cost of flying is appealing to me, but not if it
means the inconvenience of having to refuel from gas cans.

Matt

Matt wrote:
Hi everyone. I was reading about Petersen's STC to use mogas in the O-235.
Apparently the STC for the O-235 only allows premium (91 octane) to be used.
I would still be reluctant to use premium since it is a "step down" in
octane for the O-235. I would not have a problem if I was flying an O-200
and could "step up" to 87 octane since the engine was originally certified
to run on less.

Aviation fuel is rated with an octane rating that is not the same as
the (R+M/2) automotive octane rating. The traditional aviation rating
was more reliable as a guide with the WWII and 50's airliner operations
that ran such powerplants as the R-2800-CB17 at high BMEP low RPM
schedules. A normally aspirated Lyc or Continental (which would chuck
jugs through the cowling in that regime) is essentially a lightweight
farm tractor engine-it operates in a regime more similar to automotive
engines.

Premium mogas is still much cheaper than 100LL. If I had good
availablity of both fuels I would probably rin a mix of 100LL and
mogas-the effect of the TEL in the avgas will boost the mogas's octane
rating much higher than that of each fuel separately, even with as
little as 10% 100LL.

I have operated autombiles and motorcycles for years on just such a
mixture and still run my high compression BSA on just such sauce. I
know of many others running aircraft engines on this as well with good
results. Unless your STC says the tank has to be cleared of avgas
first, it is obviously legal under the STC and gives the FBO a small
revenue stream keeping him off your ass.

Premium mogas is still much cheaper than 100LL. If I had good
availablity of both fuels I would probably rin a mix of 100LL and
mogas-the effect of the TEL in the avgas will boost the mogas's octane
rating much higher than that of each fuel separately, even with as
little as 10% 100LL.

We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems. The O-200 was particularly troublesome.
Several engine overhaulers told us they had customers who had trouble
with mogas or mixes, and they had seen a bit more valve wear in those
engines.
Apparently unleaded auto fuels are refined differently and have a
significantly different composition that older engines don't like. It's
"drier," as one guy put it. When we went back to straight Avgas the
problems went away.
Lycoming won't warranty their engines if mogas is used in them.

Dan

wrote:
Premium mogas is still much cheaper than 100LL. If I had good
availablity of both fuels I would probably rin a mix of 100LL and
mogas-the effect of the TEL in the avgas will boost the mogas's octane
rating much higher than that of each fuel separately, even with as
little as 10% 100LL.

We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems. The O-200 was particularly troublesome.
Several engine overhaulers told us they had customers who had trouble
with mogas or mixes, and they had seen a bit more valve wear in those
engines.
Apparently unleaded auto fuels are refined differently and have a
significantly different composition that older engines don't like. It's
"drier," as one guy put it. When we went back to straight Avgas the
problems went away.
Lycoming won't warranty their engines if mogas is used in them.

If you want to stay in the air, it's a matter of making the engine fit
the fuel instread of the other way around. All my flying was done on
C-85/95s on mogas with a small amount of Marvel Mystery Oil and AFAIK
they never had problems.

There are airboat and amusement park operators running Lycs and
Continentals on propane, and they aren't seizing valves. There were
wind machine operators in West Coast citrus groves running big surplus
Pratts and Wrights on propane and natural gas too, and they ran for
five or ten times normal TBO and when they did let go it was usually
lower end failure-they'd seize and take the pole with them sometimes.

Dan

wrote in message oups.com...
Premium mogas is still much cheaper than 100LL. If I had good
availablity of both fuels I would probably rin a mix of 100LL and
mogas-the effect of the TEL in the avgas will boost the mogas's octane
rating much higher than that of each fuel separately, even with as
little as 10% 100LL.

We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems. The O-200 was particularly troublesome.
Several engine overhaulers told us they had customers who had trouble
with mogas or mixes, and they had seen a bit more valve wear in those
engines.
Apparently unleaded auto fuels are refined differently and have a
significantly different composition that older engines don't like. It's
"drier," as one guy put it. When we went back to straight Avgas the
problems went away.
Lycoming won't warranty their engines if mogas is used in them.

Dan


No problems at all running the O-300 in the 172 on regular old STC OK 87 octane mogas. Gets a sooty belly though...

wrote in message
oups.com...
Premium mogas is still much cheaper than 100LL. If I had good
availablity of both fuels I would probably rin a mix of 100LL and
mogas-the effect of the TEL in the avgas will boost the mogas's octane
rating much higher than that of each fuel separately, even with as
little as 10% 100LL.

We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems. The O-200 was particularly troublesome.
Several engine overhaulers told us they had customers who had trouble
with mogas or mixes, and they had seen a bit more valve wear in those
engines.
Apparently unleaded auto fuels are refined differently and have a
significantly different composition that older engines don't like. It's
"drier," as one guy put it. When we went back to straight Avgas the
problems went away.
Lycoming won't warranty their engines if mogas is used in them.

Dan

My O-200 runs outstanding on mogas. The less lead the better. The C
series and O-200 were designed to run with 0% lead. Other than the fact
100LL smells better than mogas there is absolutely no reason to use it.

wrote:

We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems. The O-200 was particularly troublesome.

My experience was the opposite. I had more trouble with 100LL than with Amoco
high-test.

George Patterson
We don't stop playing because we grow old. We grow old because we stop
playing.

On 2005-11-22, wrote:
We used to do that with both O-320s and O-200s, and both gave
trouble on either straight mogas or the mix. Unleaded auto fuel is
significantly different from Avgas, and even getting the lead level up
to 0.5 ml/l with a 75/25 mix (to make it the same as 80 octane), we had
valve sticking problems.

Interestingly, we ran our Continental C-85 in the C140 on straight
avgas continously - it caused sticking valves.

We have an O-320 in the tow plane at the glider club that mostly runs on
mogas. Runs very sweetly - not even a hint of sticking valves or other
problems.

--
Dylan Smith, Port St Mary, Isle of Man
Flying: http://www.dylansmith.net
Oolite-Linux: an Elite tribute: http://oolite-linux.berlios.de
Frontier Elite Universe: http://www.alioth.net

Matt wrote:

I would still be reluctant to use premium since it is a "step down" in
octane for the O-235.

Do you have Lycoming's owners' manual for the engine? I think you'll find that
it was certified for much lower octane than 100.

George Patterson
We don't stop playing because we grow old. We grow old because we stop
playing.

"Matt" wrote in message
. ..
Hi everyone. I was reading about Petersen's STC to use mogas in the
O-235. Apparently the STC for the O-235 only allows premium (91 octane) to
be used. I would still be reluctant to use premium since it is a "step
down" in octane for the O-235. I would not have a problem if I was flying
an O-200 and could "step up" to 87 octane since the engine was originally
certified to run on less.

Has anyone ever found premium available for aircraft use at an airport?
To tell the truth, I have never flown into an airport with mogas
available. The chance to cut down the cost of flying is appealing to me,
but not if it means the inconvenience of having to refuel from gas cans.

Matt

Matt,
I've got one of the STCs for my 152 and used to use mogas (91) very
frequently. The O235 ran perfectly on it and I put well over 1000 hours on
my previous engine using mogas 90% of the time. (a tank of 100LL once in a
while as the STC recommends).

I put in a factory OH engine about 6 years ago and although I've paid and
transferred the STC to the new engine, I have not used it for two reasons.

First, the factory warranty is void if used during the warranty period.

Second, most if not all mogas in my area now contains some alcohol, which is
not acceptable.

Yes I had to refuel from gas cans, and a careful grounding scheme should be
used along with conductive fuel handling equipment. It was a hassle. I
have never found premium gas at an airport.

The O235 in your 152 is really a medium compression engine and the 91 octane
(R+M)/2 is just fine. The lack of lead in the gas is very good for the Lyc
O235 which tends to foul the lower plugs with lead deposits, even with
aggressive leaning. Just use some 100LL on occasion to keep the valves
happy.

John Severyn