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AVGAS 100 LL vs UL 91/96 vs Mogas

HansR

Active Member
Hi,

what are you running your Lycomings on?

As far as I understand the Lycoming writing, lead is not needed. However, they strongly advise not to use pump gas.
Now, in Sweden we do not have Mogas (but we have UL 91/96). When Lycoming is writing Mogas, what does it actually mean? Is it any alcohol in it?

Do you run your Lycomings on fuel also containing alcohol? Any problems with damage rubber?

Do you also run on pump gas? Any problems?

Here I have the choice of running on 100LL, UL91/96 or Pump gas. I will not tell you what we pay for 100LL, you would not believe it anyway. If Lycoming engines runs fine on pump gas with 5% ethanol, it would save me alot.
 
Hans - welcome to the forum. Your questions have been discussed many times here, so some prudent use of the "search" function will no doubt yield much good reading material and much beneficial education.

From personal experience, I have used 91 octane 0% ethanol mogas for years in both Lycoming and Continental engines. On the recommendation of the much-respected Mahlon Russell (ex of Mattituck), I broke our new O-360 in using 100% 100LL. His recommendation was based on the need for lead in the first hours to aid in what essentially is heat curing of the exhaust valve seats. Wish I could find his post where that recommendation was made but I haven't been able to find it here today.

At about 30 hours engine time I started to introduce 91 octane mogas but so far, with a little over 50 hours on the engine, I have not gone above a 50% mixture of mogas yet, but will eventually run likely on 100% mogas. As with Sweden, here in Canada the price differential between Avgas and Mogas is substantial, so burning Mogas results in about a 30% reduction in fuel costs.

As far as ethanol and rubber components, those who have run ethanol seem to indicate most of the troubles encountered were not in the engine but in ancillary components like fuel tank quick drain valve o-rings, selector valves etc.
 
Welcome!

I will not tell you what we pay for 100LL, you would not believe it anyway.

Hans please do tell. I've been to some remote places and experienced unimaginable prices for avgas and oil (paid $20 for 1 quart of oil in Canada once). Would love to know cost and availability in Sweden.
 
Lead for breakin ?

I used 100LL for breakin per popular perception. Does anyone know what Lycoming and Superior say as "official" instructions ?
 
Hans,

A lot of us here in the USA are running 91 octane (US rating system for car gas) ethanol-free car gas in the low to medium compression 7-1 to 8.5-1) Lycs. I'd be a little uncomfortable with the idea in an angle valve IO-360, but I've never actually tried it.

Some are running 91 octane car gas containing ethanol, with no ill effects. The biggest deal, long term, about running e-gas is that older mechanical fuel pumps have soft parts that are attacked by ethanol. According to an engineer at Tempest, their newer production pumps use soft parts that are ethanol resistant, though they don't 'advertise' that. If I ever update my mechanical pump, I'll seriously consider running e-gas. It's much easier to get, closer to my home airfield.

Here in the USA, where our temperatures may get higher than yours, the short term big deal is that car gas usually has a higher vapor pressure than avgas. This is especially true for 'winter blend' car gas, and it's worse in some parts of the country than others, depending on local rules and refiners' policies. This can lead to 'vapor lock', which can show up in either traditional fuel delivery system but might be worse in carb'd engines because the fuel is at lower pressure in the lines, and at atmospheric pressure in the carb.

As a practical matter, some have major problems, while others have no issues at all running car gas. In around 20 years of running e-free mogas in 160 & 180 HP carb'd Lycs, I've had one incident. I made the mistake of running winter blend (higher vapor pressure) gas on a 100+ degree day, and after a short flight and a ground heat soak, had rough running after takeoff.

Charlie

edit: To test for e-gas, you can use the kit Bill linked, or any tall thin clear jar with a lid. I use an old olive jar. I mark it about 1" up from the bottom, add water to the mark, and then fill with the gas I'm testing. Give it a good shake and watch as the water settles out. If the water level appears to be higher than before, it has alcohol in it.
 
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I suppose I'm a bit higher on compression than most others doing it at 8.7:1, but I've put just over 200 hours so far on my IO360 with 91 octane auto fuel here in Texas temps. I've done several things to my fuel system to alleviate the heat-related problems that you'll encounter with autofuel (especially ethanol blends), but I've had zero engine-specific problems. At $3.40/gal for fuel it makes a difference.
 
bench mark compression.

This is just us, but we do watch our EGT' and CHT close at all times.
We run an IO-360 "P" valve with 9:1 compression pistons. We do have all 8 oil jets installed to help with piston cooling as well. We have learned down through the years that 9:1 is a good place to bench-mark using the high grade fuels. How hard or hot your run your engine will modify that to a grate degree.
We play it safe and run 100LL for the first 50-80 hours of brake-in. Then use 93 U with no E at a 50% or above mix in the winter and sometimes higher in the hot summer or even 100% 100LL in a very hot summer time. We know that if our compression was say 7.5:1 we would be running 82-83 U with as much as 15% E. But that is the low end of the compression range for these engines and a lot less BMEP on them. The "E" in the fuels these days will attack
some of the older rubber seals and gaskets in the older fuel systems. It is best to take a close look at your seals and gaskets to see if they will hold up to the newer E fuels. Most of the newer fuel system makers have switched their parts to replace the older rubber seals with ones that will stand up to the newer fuels with some degree of E in them.
Always watch your EGT's and CHT's, if you see any sudden spikes no matter what fuels you are using, be ready to back out of the throttle and keep that engine as cool as you can tell you get a handle on if it's the grade of fuel you have loaded or the heat of the climb and summer that it getting you. Keeping the BMEP down makes them last longer. I know we all like to have fun as well, I do too.

Hope this helps, Yours, R.E.A. III # 80888
 
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Hans, you may want to read Lycoming Service Instruction No. 1070Z found here (https://www.lycoming.com/sites/default/files/SI1070Z Specified Fuels.pdf). It discusses all the various fuels approved and/or acceptable in Lycoming engines. Table 2 and its notes seem relevant. Good luck, Russ

Thanks, first time I see automotive fuel being recommended by Lycoming!
No question I can run on Hjelmco 91/96, so at least I do not have to use 100LL.

However, they also accept automotive fuel that fulfills EN 228. Now, we have a lot of fuel that is fulfilling EN 228, but with additives, one of those being ethanol. I will contact the manufacturers to find out if ethanol free fuel is available anywhere.
 
Hans please do tell. I've been to some remote places and experienced unimaginable prices for avgas and oil (paid $20 for 1 quart of oil in Canada once). Would love to know cost and availability in Sweden.

You saw the response from control? and thats for UL 91/96. 100LL is another 25% or so.
 
Hans,

Here in the USA, where our temperatures may get higher than yours, the short term big deal is that car gas usually has a higher vapor pressure than avgas. This is especially true for 'winter blend' car gas, and it's worse in some parts of the country than others, depending on local rules and refiners' policies. This can lead to 'vapor lock', which can show up in either traditional fuel delivery system but might be worse in carb'd engines because the fuel is at lower pressure in the lines, and at atmospheric pressure in the carb.

As a practical matter, some have major problems, while others have no issues at all running car gas. In around 20 years of running e-free mogas in 160 & 180 HP carb'd Lycs, I've had one incident. I made the mistake of running winter blend (higher vapor pressure) gas on a 100+ degree day, and after a short flight and a ground heat soak, had rough running after takeoff.

Charlie

I have run a Rotax 912 several years with auto fuel with ethanol for many years. A couple of days ago, it was very hard to start in very hot weather conditions. Maybe a vapor lock.

Is vapor lock basically a problem when the aircraft has been om ground for a while with no cooling wind? If the vapor lock is not likely to happen in mid flight, it is not a big concern. what do you think, is vapor lock likely also in flight, and what will happen. Total engine failure, or only a while of rough running?

We do not get 100 F, but this summer we have had 90 several days.

Yes, ethanol testing is a good idea, but first I will find out if there at all is such a ting as ethanol free auto gas in Sweden.
 
As it has been mentioned before, the key things to be aware of when thinking about auto fuel/MOGAS are as follows:

1. Gas with ethanol in it is really only a concern to some of the soft components, such as rubber, that may be part of your fuel system. The actual engine itself doesn't care if ethanol is present or not....it'll run just fine either way. If you're going to use fuel that has ethanol in it just be sure that you're constantly running fresh fuel. You don't want ethanol laced fuel to set up for any length of time. Non ethanol laced auto fuels have a fairly long shelf life...but still not as long as 100LL.

2. Vapor lock will most likely to only occur in a heat soaked engine that's on the ground and you're trying to start it. I guess it's possible to occur when in flight, but I've never heard of it. The higher vapor pressures of auto fuels are another subject, but I'm only talking about vapor lock in a heat-soaked environment here. The key to preventing vapor lock is to get the fuel flowing. That's why a fuel injected engine that has a fuel rail with a return line and has cool fuel constantly flowing around the system will never experience vapor lock. If you have a carburetor it's also very important to have a way to "sweep" that hot fuel out of the system. Even a very small 1/8" return line that you can control as to when it's opened or close to sweep that hot fuel away will do the trick. As it's been discussed many times here, shielding the fuel lines from heat is important but all the shielding in the world isn't going to prevent vapor lock. The only way to insure against it is to keep that fuel moving.

So IMO, the moral to the story is to run what you want...if your fuel system components can tolerate it, and keep that cool fuel moving!!

Mark
 
You can still get vapor lock in flight given high altitude and high temperature with mogas at the pump inlet, especially easy with winter gas on a summer day. Some Rotax folks have reported it right here on VAF.
 
You can still get vapor lock in flight given high altitude and high temperature with mogas at the pump inlet, especially easy with winter gas on a summer day. Some Rotax folks have reported it right here on VAF.

I've seen that myself, especially when taking off after the airplane is sitting out on the ramp in the sun for a few hours at 100F outside air temps. Usually climbing through about 6000' I'll see low fuel pressure that is persistent for maybe 10 minutes until the fuel in the tanks starts to cool down in the slipstream, then it's fine. Mogas or 91E10 will do this pretty regularly under those conditions, 100LL is much less likely.
 
Also, how tightly are we defining 'vapor lock'? Remember, if you have a carb'd engine, fuel can boil in the float bowl. If the fuel in the tank has heat soaked in really high temps (as was the case for me in my incident), you might be ok when you first push the throttle open, but by the time you're off the ground good the oil, sump, and carb have heated up even more due to full engine output. The combo could make the fuel boil in the carb *after takeoff*. I'm fairly confident that's what happened to me.

Note that I've never had an issue in hot weather while running summer mogas. And after my incident, I removed the gascolator (which sat directly in the exit for the engine's cooling air). While I have no intention of testing the theory, I suspect I'd be ok now even with winter blend.

Hans,

One thing you should check is whether methanol is ever used in Europe. Here in the USA, all we ever get is ethanol. Ethanol doesn't have highly corrosive properties on aluminum, but the same can't be said for methanol. I doubt you'd have it; I'm just mentioning it because I have no experience with European fuel standards and you want to cover all your bases. If Euro aviation agencies allow the use of mogas, you're probably safe on that property.

Charlie
 
Swedish EN228

Thanks again, good information.

My current conclusion is that I will run automotive fuel if I can get it ethanol free. It seems that 98 octane (RON) is likely to sometimes be ethanol free in summer time.

However, now I have contact info to an expert at Preem Sweden, that should now all about it, on vacation though.... Coming back next week.

If this turns out positive, it might reduce cost for a lot of pilots in Sweden!

/ HR
 
Hans please do tell. I've been to some remote places and experienced unimaginable prices for avgas and oil (paid $20 for 1 quart of oil in Canada once). Would love to know cost and availability in Sweden.

I see 100LL is around $9.65 per US gallon, the latest prices I could find were from 2017.
 
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