Mixing Mogas and Avgas
Join Date: Jan 2008
Location: Canada
Posts: 631
Likes: 0
Received 0 Likes
on
0 Posts
The mag timing of the O-200 is related to an AD, which was associated with certain cylinders. I know that my O-200, with it's new cylinders, is not longer subject to that AD< and as such, it is timed to 28 BTC, and I run both Mogas, and occasionally Avgas (so certainly mixtures of both).
Mogas containing alcohol is prohibited in Cessnas, and unwise to run.
My experience (about 3400 hours flying Mogas in many models of Cessnas) has demonstrated not greater propensity to carb ice on Mogas, than on Avgas. I recall the specs for Mogas suggesting a slightly greater susceptibility to carb ice on Mogas, but in the practical world, that has not been my experience. I do have a carb air temp indicator installed though.
I did high altitude testing of Mogas in a 182 and 180; Up to 13,000 feet, and 19C, and have never had a problem with Mogas.
I think you should expect non alcohol Mogas, and Avgas to be operationally the same. Aside from a black exhaust residue for Mogas, I think that otherwise the differences between the gasolines would be indistinguishable to the pilot in an approved Continetal......
Mogas containing alcohol is prohibited in Cessnas, and unwise to run.
My experience (about 3400 hours flying Mogas in many models of Cessnas) has demonstrated not greater propensity to carb ice on Mogas, than on Avgas. I recall the specs for Mogas suggesting a slightly greater susceptibility to carb ice on Mogas, but in the practical world, that has not been my experience. I do have a carb air temp indicator installed though.
I did high altitude testing of Mogas in a 182 and 180; Up to 13,000 feet, and 19C, and have never had a problem with Mogas.
I think you should expect non alcohol Mogas, and Avgas to be operationally the same. Aside from a black exhaust residue for Mogas, I think that otherwise the differences between the gasolines would be indistinguishable to the pilot in an approved Continetal......
...UL91... Whatever that is.
Check that your aircraft is approved to use it though, as approval for MOGAS doesn't automatically include UL91.
MJ
Join Date: Mar 2014
Location: The World
Posts: 1,271
Likes: 0
Received 0 Likes
on
0 Posts
@Blue Albatross: Did you read the papers, which came with your certification?
I only know STC's with a big pile of paper, some filler cap sticker which answer the question already, and a paper to keep at the POH in the plane stating the same. On mine it says certified for Autofuel/UL91/100LL in any mixtures, both in the extended documentation and on the sticker. BTW - it also says Autofuel STC, not "Mogas" STC ...
Speaking of UL91, this is simply Avgas without the lead. This brew is much closer to the specs the old engine were built for, compared to 100LL - for which the old O-200/O-300 were never certified to run, though ;-).
"Mogas" usually is standard car gasoline with special overlooking to avoid ethanol in it. Even though some state the standard tap gasoline is not appropriate for aviation, I have my doubts that this is more protection of UL91 and Mogas business. Such as Total (selling Mogas) states there are additions for modern car engines in their premium plus gasoline, it may or may not have an effect on us. I was running an old O-300 on Aral Ultimate for a long time, which is ethanol free because they replaced it with ether and therefore covered by the autofuel STC, which was fine except for two thing: there is some yellow stuff not burning totally and spread over the place and the engine runs a bit hotter compared to Avgas, so you have to keep an eye on EGT/CHT.
One word to the ice on carb - yes, there is a physical evidence for something called Mpemba effect, which may cause Mogas run carb engines to encounter earlier ice pickup. The effect is more prominent at hot liquids, so this may also count for the temperature limits of using Mogas. Personally, I have run Autofuel (of various kind and sometimes dubious origin) in hot environments and never encountered that effect - though some bubbling trouble at hot&high.
I only know STC's with a big pile of paper, some filler cap sticker which answer the question already, and a paper to keep at the POH in the plane stating the same. On mine it says certified for Autofuel/UL91/100LL in any mixtures, both in the extended documentation and on the sticker. BTW - it also says Autofuel STC, not "Mogas" STC ...
Speaking of UL91, this is simply Avgas without the lead. This brew is much closer to the specs the old engine were built for, compared to 100LL - for which the old O-200/O-300 were never certified to run, though ;-).
"Mogas" usually is standard car gasoline with special overlooking to avoid ethanol in it. Even though some state the standard tap gasoline is not appropriate for aviation, I have my doubts that this is more protection of UL91 and Mogas business. Such as Total (selling Mogas) states there are additions for modern car engines in their premium plus gasoline, it may or may not have an effect on us. I was running an old O-300 on Aral Ultimate for a long time, which is ethanol free because they replaced it with ether and therefore covered by the autofuel STC, which was fine except for two thing: there is some yellow stuff not burning totally and spread over the place and the engine runs a bit hotter compared to Avgas, so you have to keep an eye on EGT/CHT.
One word to the ice on carb - yes, there is a physical evidence for something called Mpemba effect, which may cause Mogas run carb engines to encounter earlier ice pickup. The effect is more prominent at hot liquids, so this may also count for the temperature limits of using Mogas. Personally, I have run Autofuel (of various kind and sometimes dubious origin) in hot environments and never encountered that effect - though some bubbling trouble at hot&high.
Join Date: Jan 2008
Location: Canada
Posts: 631
Likes: 0
Received 0 Likes
on
0 Posts
Did you read the papers, which came with your certification?
"Mogas", "Autofuel" and "Autogas" are more colloquial terms, and might be used somewhat interchangeably. It doesn't really matter if you're using gasoline which meets the specified standard.
engine runs a bit hotter compared to Avgas, so you have to keep an eye on EGT/CHT.
Join Date: Mar 2014
Location: The World
Posts: 1,271
Likes: 0
Received 0 Likes
on
0 Posts
I agree, it is a crucial point to get to know what we put in our tanks and "Mogas" requires quite some studies to do it right.
For example, I am running my O300 on a Petersen Autofuel STC - fuel allowed from gasoline taps for cars, with max. 1% Ethanol content and min ROZ 98 (EN228, ASTM D-439/D-4814, (ROZ+MOZ)/2 >87 octane). When I started to study the issue, I was amazed how few people knew ROZ/MOZ/Octane settings. In central Europe many times you can easily get "Super Plus/Premium" with ROZ 98, but you have to have a look at additives and ethanol (EN228 was changed and now has up to 5% ethanol, they tossed the E Zero signs ...).
At airfields, I am always a bit suspicious about the Mogas they give you - many times they do not follow the tap labelling requirements of car stations. I remember my last flight in Germany, where we found out by surprise, that they sold us ROZ 95 E5 as "Mogas", which is not what I would expect in a civilized country. Ok, may be disputable with civilization now there ... I did not really notice a difference in burning that in an old C172, except for some higher EGT.
I had a look at EGT/CHT and indeed, the O300 runs noticeably hotter on Mogas, with ROZ 102-98-85 in hotter running series. I hot summer I was running the engine very LOP, but this I can do with 100LL and 102, but with ROZ 98 I even get hot coloring in the painting of the back of the exhaust when going all the way LOP.
For example, I am running my O300 on a Petersen Autofuel STC - fuel allowed from gasoline taps for cars, with max. 1% Ethanol content and min ROZ 98 (EN228, ASTM D-439/D-4814, (ROZ+MOZ)/2 >87 octane). When I started to study the issue, I was amazed how few people knew ROZ/MOZ/Octane settings. In central Europe many times you can easily get "Super Plus/Premium" with ROZ 98, but you have to have a look at additives and ethanol (EN228 was changed and now has up to 5% ethanol, they tossed the E Zero signs ...).
At airfields, I am always a bit suspicious about the Mogas they give you - many times they do not follow the tap labelling requirements of car stations. I remember my last flight in Germany, where we found out by surprise, that they sold us ROZ 95 E5 as "Mogas", which is not what I would expect in a civilized country. Ok, may be disputable with civilization now there ... I did not really notice a difference in burning that in an old C172, except for some higher EGT.
I had a look at EGT/CHT and indeed, the O300 runs noticeably hotter on Mogas, with ROZ 102-98-85 in hotter running series. I hot summer I was running the engine very LOP, but this I can do with 100LL and 102, but with ROZ 98 I even get hot coloring in the painting of the back of the exhaust when going all the way LOP.
