More questions re: autogas

[JOhnH]

The current thread about auto gas got me to thinking about my issue, so in order to keep from hijacking that thread I started a new one.

Ever since I bought my 1977 Cessna 172n I have had a problem with high CHTs. The plane has the 180hp upgrade and it also has the mogas STC. But I have never run mogas in it.

To further muddy the question, the original engine that had the mogas STC blew up a few years ago and I had to replace it.

Would the STC still be good? Could the fuel mods for mo gas have anything to do with the high CHT when running 100LL? If it does have anything to do with it, I need to find out how to reverse it. I can buy 80 octane non-ethanol gasoline at a local bottled gas company but that would really be a pain to haul to the hangar and pour in manually. I THINK this gas is unleaded, but I am not sure. and my hangar lease forbids gas cans for fire regulation compliance.

I guess I will need to dig out and read that STC. But in the meantime, any thoughts?

 

[Capt. Geoffrey Thorpe]

I doubt that installing the placards and making the log entry for the auto gas STC would cause high CHTs.

 

[JOhnH]

I doubt that installing the placards and making the log entry for the auto gas STC would cause high CHTs.

That's what I always figured, but in the other thread there were a couple of comments that seemed to indicate that on some planes/engines, extensive modifications must be made. I don't have a copy of the STC at home so I was trying to find the answer on line. No luck so far, and I have to give up for a few hours now.

 

[denverpilot]

There's no mods done for a Skyhawk MoGas STC. That's how dumb it is. You're just paying someone for having jumped through FAAs hoops to prove the engine would still run on what it ran on, the day it came from the factory.

Most high CHT issues on Cessnas, start looking at the cowling baffles first. You'll probably find them cracked, broken, chunks missing, and definitely nothing like they came from the factory.

Any place air can pass through them instead of down through the fins, means less cylinder cooling. Stick your hand out the car window at a 45 and push some air down at 100 MPH. That's what that wimpy little piece of silicone is trying to do. Now poke a hole in your hand... Ha. Kidding. Quite a bit less effective with the hole, right?

Then realize that no one had engine monitors for the first ten to fifteen years of the aircraft's life, longer if it's not a 70s airplane. People blew cylinders and sucked valves all the time but pulling a jug and replacing it was something that was expected and cheap. Was it because of high CHT? No one knows.

Everyone also flew around hellaciously rich. That carries some heat away and is still an option.

Pulling jugs isn't considered no big deal anymore and it's getting damn hard to find a company that can make jugs that don't self-destruct nowadays for some reason, too. Catch-22.

 

[Capt. Geoffrey Thorpe]

That's what I always figured, but in the other thread there were a couple of comments that seemed to indicate that on some planes/engines, extensive modifications must be made. I don't have a copy of the STC at home so I was trying to find the answer on line. No luck so far, and I have to give up for a few hours now.

http://www.eaa.org/autofuel/autogas/stc.asp

http://www.autofuelstc.com/stc_specs.phtml

 

[Jeff K]

Would the STC still be good?

Well look at it. It should list the airframe and engine. It might even list your N number. The only way it wouldn't be good is if it listed the specific engine serial number and/or you changed the engine type.

Could the fuel mods for mo gas have anything to do with the high CHT when running 100LL?

No. It's possible to get high CHT's by running too low an octane gas (the onset of detonation... bad news) but this is the opposite issue. 100LL might give you lead fouling in your spark plugs.

I guess I will need to dig out and read that STC. But in the meantime, any thoughts?

Read the STC and see if it's keyed to a specific engine and serial number.

Otherwise, find a source of ethanol free unleaded and burn alot of it. If you don't have the STC, you need to get a copy of it to remain paperwork legal with the FAA. I think Peterson is pretty good about that although a charge might be involved.

 

[JOhnH]

There's no mods done for a Skyhawk MoGas STC. That's how dumb it is. You're just paying someone for having jumped through FAAs hoops to prove the engine would still run on what it ran on, the day it came from the factory.

I was afraid that was the case, although I have no problem paying someone for their research.

Most high CHT issues on Cessnas, start looking at the cowling baffles first. You'll probably find them cracked, broken, chunks missing, and definitely nothing like they came from the factory.

I have been chasing this high CHT problem for years. All of the seals have been replaced and double checked. 3 A&Ps and 2 IAs have gone through it and verified seals, baffles, timing and anything else they could think of. We have calibrated and swapped CHT probes around. I even had the oil cooler relocated on the advice of Lycoming and an IA. I still have one cylinder (#4) that consistently runs at 400 or above unless I run full rich at low power. (We do intend to go up with Henning again and have him go over his LOP procedure for us). He went up with us once but the OAT was not very high that day.

Then realize that no one had engine monitors for the first ten to fifteen years of the aircraft's life, longer if it's not a 70s airplane. People blew cylinders and sucked valves all the time but pulling a jug and replacing it was something that was expected and cheap. Was it because of high CHT? No one knows.

This is what my A&P keeps telling me. He will love the day I tell him to rip that damn edm 700 out of there and replace it with a cigarette lighter. But I just don't like flying around with one cylinder showing 360 and another showing 410.

Everyone also flew around hellaciously rich. That carries some heat away and is still an option.

A very expensive one, although not as expensive as engine work.

Pulling jugs isn't considered no big deal anymore and it's getting damn hard to find a company that can make jugs that don't self-destruct nowadays for some reason, too. Catch-22.

I suspect that is what I will be doing on #4 one day. So far it has a compression of 77/80 with about 250 hrs on it.

 

[Geico266]

Have you tested the sensors in boiling water to make sure they are accurate? Water boils at 212F. This is what your gage should read is a rolling boil.

 

[NoHeat]

Have you tested the sensors in boiling water to make sure they are accurate? Water boils at 212F.

You live in Nebraska, right?

I'd bet water boils a few degrees colder, for you. Because your pressure altitude isn't sea level. Subtract two degrees F per 1000 ft of altitude to get the right boiling point, if you are doing a calibration.

Anyway, the OP said one cylinder is hotter, regardless which probe is swapped to that cylinder, so probe calibration is probably not the problem. There is a chance the problem could be a bad probe connector, though.

 

[Geico266]

Have you looked for intake leaks in #4 cylinder intake system?

 

[Skylane81E]

What fuel does your current engine require, you might find that it requires 100LL and no auto fuel STC is available for such a thing.

 

[N801BH]

DON'T trust the octane number posted on the pump....

 

[Skylane81E]

Mmmmm

 

[N801BH]

Mmmmm

Of course I killed it by testing the upper limits of how hot I could get the EGT's..

Ran for 300 hours at 1725f..... It lasted about 4 minutes at 1775f..


For reference .. This motor was running at 1425f... Mine runs /ran 300 degrees hotter..

 

[charlie]

You will find that the STC for mogas in the 180 does not make it eligible to run 87 oct therefore the ethanol free 80 oct will not be legal or a good idea to try in your 180. With regard to your CHT you probably have a 10-3878 carburetor which is often too lean for the 172 installation. Charlie Melot Zephyr Engines

 

[JOhnH]

Have you looked for intake leaks in #4 cylinder intake system?

One of the last things my A&P did was repair a couple of very small intake leaks. I had high hopes, but it had very little, if any effect.

 

[JOhnH]

What fuel does your current engine require, you might find that it requires 100LL and no auto fuel STC is available for such a thing.

Although a previous owner did get the auto fuel STC, I have never run anything but 100ll, which is what the stenciling by the fuel caps says to run.

 

[JOhnH]

You will find that the STC for mogas in the 180 does not make it eligible to run 87 oct therefore the ethanol free 80 oct will not be legal or a good idea to try in your 180.

That is what I figured. And I would definitely have checked that out had I even thought about going through the hassle of buying cans of it an hauling it to the plane. So that was never an intention, just an observation.

With regard to your CHT you probably have a 10-3878 carburetor which is often too lean for the 172 installation. Charlie Melot Zephyr Engines

I wondered about that. In another thread someone said they resolved various problems in a 180 when they discovered it had the wrong carb. Last week I asked my A&P about that but he is on vacation and won't be back for a few days. How would I find out the correct carb? I have the parts list from the original Pen Yan STC, but the Pen Yan conversion (circa 1985) bought the farm in 2010 and a rebuilt 180 from another rebuilder was installed. Off the top of my head, I don't know if a new carb came with the new engine or not. Would it be safe to say the same carb specified in the Pen Yan STC would still be the correct one?

 

[JOhnH]

With regard to your CHT you probably have a 10-3878 carburetor which is often too lean for the 172 installation. Charlie Melot Zephyr Engines

I just checked the engine log and the attached Authorized Release Certificate does indicate that the carb is an overhauled PN 10-3878.

Can you advise the correct (or better) carb, or at least where I can find that out?

 

[Geico266]

You will find that the STC for mogas in the 180 does not make it eligible to run 87 oct therefore the ethanol free 80 oct will not be legal or a good idea to try in your 180. With regard to your CHT you probably have a 10-3878 carburetor which is often too lean for the 172 installation. Charlie Melot Zephyr Engines

Nice catch Charlie.

 

[N801BH]

Nice catch Charlie.

Hmmmm...

All fuels I have seen are labeled.... minimum..... 85 octane, then 87 and then 91.....

Where are the 80 octane fuels sold ??

 

[JOhnH]

Hmmmm...

All fuels I have seen are labeled.... minimum..... 85 octane, then 87 and then 91.....

Where are the 80 octane fuels sold ??

I was going from memory. I was only in there once and I was looking for "high octane" non-ethanol. What I saw was low octane. I might have the number wrong but it was lower than I was looking for for my generator. Hurricane season is upon us and ethanol sucks for generators.

 

[N801BH]

Hurricane season is upon us and ethanol sucks for generators.

Agreed.... Ethanol kills most fuel systems....

As for Hurricane season... I was born and raised in Miami... I feel your pain...

A survivor of Donna, Betsy, Cleo and dozens of other Hurricanes..

 

[charlie]

I just checked the engine log and the attached Authorized Release Certificate does indicate that the carb is an overhauled PN 10-3878.

Can you advise the correct (or better) carb, or at least where I can find that out?

FWIW the 10-3878 is a correct carb but not always the best one. I seems to vary from one engine to the next. I am in Jasper AB winding up a month of touring. I'll be back in FL on Wednesday and lookat the carb options.

 

[moonshine]

...
Read the STC and see if it's keyed to a specific engine and serial number.
...

Should be. I remember having to call Petersen to renew the STC on one of the airplanes as the engine was replaced since the STC issuance. Paid half of what the STC cost ($0.75 /hp vs. $1.50 /hp or whatever it is these days)

 

[SoloEqs]

Hmmmm...

All fuels I have seen are labeled.... minimum..... 85 octane, then 87 and then 91.....

Where are the 80 octane fuels sold ??

There are a couple of different ways to determine octane rating. 87 RESEARCH octane rating is about 80 MOTOR octane rating, which is where we get the "80/87" avgas number. The ratio between MON and RON varies by the compound, so 91UL (MON) is equivalent to 100LL (RON).

Non-oxygenated 87 RON is pretty much equivalent to 80/87, except there's no lead. If you have older cylinders, run a tank of 100LL every four or five fills and you will protect the valves and seats. NEWER valve seats don't need lead, so if you've have a rebuild in the last 30 years, you're probably okay running unleaded as a steady diet (check with the company that made your jugs).

 

[NineThreeKilo]

I've run both 100LL and mogas (non eth) in the same engine which was STCed, it did run a little hotter on mogas, if it means anything to you I only run 100LL now.

 

[N801BH]

There are a couple of different ways to determine octane rating. 87 RESEARCH octane rating is about 80 MOTOR octane rating, which is where we get the "80/87" avgas number. The ratio between MON and RON varies by the compound, so 91UL (MON) is equivalent to 100LL (RON).

Non-oxygenated 87 RON is pretty much equivalent to 80/87, except there's no lead. If you have older cylinders, run a tank of 100LL every four or five fills and you will protect the valves and seats. NEWER valve seats don't need lead, so if you've have a rebuild in the last 30 years, you're probably okay running unleaded as a steady diet (check with the company that made your jugs).

 

[PaulMillner]

There are a couple of different ways to determine octane rating. 87 RESEARCH octane rating is about 80 MOTOR octane rating, which is where we get the "80/87" avgas number. The ratio between MON and RON varies by the compound, so 91UL (MON) is equivalent to 100LL (RON).

Non-oxygenated 87 RON is pretty much equivalent to 80/87, except there's no lead. If you have older cylinders, run a tank of 100LL every four or five fills and you will protect the valves and seats. NEWER valve seats don't need lead, so if you've have a rebuild in the last 30 years, you're probably okay running unleaded as a steady diet (check with the company that made your jugs).

>> 87 RESEARCH octane rating is about 80 MOTOR octane rating, which is where we get the "80/87" avgas number.

Not so! The 87 in 80/87 is the rich supercharge rating that is determined under very different engine operating conditions, and on a different test engine, than the Research octane number.

As an example, the 100/130 octane ratings on 100LL are 100 MON (the avgas and mogas motor number techniques vary slightly, but are generally within one octane number of each other, so most folks ignore the difference) but about 110 Research... the 130, again, is the rich supercharge rating.

>> The ratio between MON and RON varies by the compound, so 91UL (MON) is equivalent to 100LL (RON).

91UL MON is just that. 100LL is 100 MON (Motor Octane Number). There are no RON (Research Octane Numbers) used in the avgas rating system... just MON and rich supercharge.

>> Non-oxygenated 87 RON is pretty much equivalent to 80/87, except there's no lead.

I think you're probably referring to 87 AKI that you see on the pump in the US and Canada? That's RON+MON/2... so rule of thumb, an 87 AKI (pump octane) mogas will be about 82 MON... so like you say, roughly equivalent to 80/87. For the last decade or so of manufacture, there was no lead in 80/87 either, since the blend components had gotten so good that none was required to meet octane spec, and lead costs money.

>> If you have older cylinders, run a tank of 100LL every four or five fills and you will protect the valves and seats. NEWER valve seats don't need lead

It turns out that NO valve seats need lead. Research reported both by ASTM and FAA reveal that the supposed "low lead" problems with valve seats were REALLY lower octane problems.

Paul, blend gasoline for a living mode

 

[weirdjim]

Although a previous owner did get the auto fuel STC, I have never run anything but 100ll, which is what the stenciling by the fuel caps says to run.

Stencils are cheap.

 

[Skylane81E]

Although a previous owner did get the auto fuel STC, I have never run anything but 100ll, which is what the stenciling by the fuel caps says to run.

If the placards are right no auto gas for you

 

[JOhnH]

If the placards are right no auto gas for you

I have pretty much confirmed that for several reasons.

 

[weirdjim]

I have pretty much confirmed that for several reasons.

And they are.... ?

 

[Skylane81E]

Here is the big one

You will find that the STC for mogas in the 180 does not make it eligible to run 87 oct therefore the ethanol free 80 oct will not be legal or a good idea to try in your 180. With regard to your CHT you probably have a 10-3878 carburetor which is often too lean for the 172 installation. Charlie Melot Zephyr Engines

 

[JOhnH]

And they are.... ?

Primarily the fact that it is only sold at three airports in Florida and most of them would consume a tank making the round trip.

And true or not, I have heard that some planes run hotter on Mo Gas than 100LL.

And when even the people that "Sound" like experts can't agree on technical details, I just don't have the desire or motivation to go to the trouble to carry cans of gas to my hangar and climb a ladder with those cans and try to get MOST of it in the wing tanks.

But other than that, no real reason.

Can you give me any over-riding reasons why I should reconsider?

 

[Tony_Scarpelli]

Primarily the fact that it is only sold at three airports in Florida and most of them would consume a tank making the round trip.

And true or not, I have heard that some planes run hotter on Mo Gas than 100LL.

And when even the people that "Sound" like experts can't agree on technical details, I just don't have the desire or motivation to go to the trouble to carry cans of gas to my hangar and climb a ladder with those cans and try to get MOST of it in the wing tanks.

But other than that, no real reason.

Can you give me any over-riding reasons why I should reconsider?

No you are right. You fly a Cessna you should definitely by the more expensive gas. Don't give it another thought.

 

[JOhnH]

No you are right. You fly a Cessna you should definitely by the more expensive gas. Don't give it another thought.

Since you didn't use a smiley, I have to ask: Why the attitude? Did I say something that annoyed you? Or are you saying that people that fly 36 yr old 172s must like to throw money away? Would YOU fly s 300 mile round trip to buy a load of fuel that might save you a buck or two a gallon? Or buy a truck so you can haul seven or eight 5 gallon cans of gas so you can climb a ladder to pour most of it in a little hole?

I'm sorry if I mis-read you, but your comment sounded condescending.

 

[Tony_Scarpelli]

There are two types of people those who will fly with mogas and those who wont. You do not need much motivation to talk yourself out of it. If saving $3 soon to be $4 per gallon is not enough motivation then go for it.

It has been posted over and over again that there are many sources of auto gas without E. E is added at the pump so if you find any 55 gallon can available for $10 from craigslist and then get a jobber to fill it, just ask him not to put the E in it. You will have mogas. 320s take 80 octane so you do not even need to ask for premium. Most stations that sell E in their gas also have pure premium so you could pay $.30 more per gallon and get the 93 octane.

you can also get it at any boat Marena as E is not good for boat engines. So I guess I just figure if someone says something like "there are only 3 stations" in the whole darn state that sell mogas, after all that is posted in this and many other mogas threads, I have to come to conclusion you made up your mind and you are one of those other guys. Good luck with your choice.

your attitude about it not being worth pouring gas cans into the wings....Cessna that is your decision so why ask? tractor supply will sell you a gas tank for $400 with a 12V pump and make it every bit as easy to haul from 30-150 gallons of gas in a trunk, van or Truck bed and the payback will be about 75-300 gallons of mogas. With this setup you do not even need a jobber to deliver it to you, you can go to the wholesale distribution and pick it up. It is so dead simple I just have no time or patience for those who just lack the basic motivation to check it out.

So no I am not condescending as much as just tired and bored with all the folks who apparently need permission to not buy mogas so they stack a bunch of stupid obsticals, mostly imaginary, in their own way. It matters not to me what you fly in.

 

[denverpilot]

There are two types of people those who will fly with mogas and those who wont. You do not need much motivation to talk yourself out of it. If saving $3 soon to be $4 per gallon is not enough motivation then go for it.[/ QUOTE]

$4/$5 here. As high as $6 at some airports.

It has been posted over and over again that there are many sources of auto gas without E. E is added at the pump so if you find any 55 gallon can available for $10 from craigslist and then get a jobber to fill it, just ask him not to put the E in it. You will have mogas.

E is not added at the pump here. At all.

you can also get it at any boat Marena as E is not good for boat engines. [/QUOTE ]

Actually it kills fish. Government doesn't give a crap if something is bad for your boat engine.

Tractor supply will sell you a gas tank for $400 with a 12V pump and make it every bit as easy to haul from 30-150 gallons of gas in a trunk, van or Truck bed and the payback will be about 75-300 gallons of mogas. With this setup you do not even need a jobber to deliver it to you, you can go to the wholesale distribution and pick it up.

That was going well until wholesale. Around here you need a wholesale license to buy stuff wholesale. And there aren't any wholesale sales of fuel anyway except by the multiple-truckload at the refinery. We have one. And a tiny pipeline for gas from Wyoming.

Every gas station buys from them. Additives are bottled and added at the station tank but not E. It's blended at the refinery. Some brands big enough to own/lease tankage at the terminal do pay for pre-blending their stuff. Depends on the brand and their volume and what they want to store for hedging.

It is so dead simple I just have no time or patience for those who just lack the basic motivation to check it out.

So no I am not condescending as much as just tired and bored with all the folks who apparently need permission to not buy mogas so they stack a bunch of stupid obsticals, mostly imaginary, in their own way. It matters not to me what you fly in.

I agree with your sentiment completely that MoGas CAN be a good idea for some, but you need to check se of your other facts.

We have a MoGas STC. I don't utilize it at home base because the economics of the purchase of a legal tank, pump, filter, and the possible ticking off of the Airport Authority and FBOs isn't worth it. 30 miles to drive for the closest Ethanol free fuel (at a racing distributor as I mentioned before, not a wholesaler) one-way, eats up most of the $1/gal benefit in transportation costs. Amortize the cost of the delivery devices too, and it's three years if flying to break even. We've run the numbers. That's assuming the same guy who has the pickup truck wants to drive over for fuel for three LLC co-owners every time or the pickup truck is "community" property.

Not that we haven't tried anyway. We had military fuel bladders. Those were entertaining to say the least. We have a custom built tank trailer available if the disparity between MoGas and 100LL stays at or above $2/gal. We buy MoGas at airports that have it.

The reality locally is... It isn't worth it. It's close. Your assumptions don't match every possible circumstance. Just be aware of that when you preach to the choir. If I were retired, the time to fart around with it would be a nice hobby.

 

[wabower]

Tell me where to find the closest provider of mogas for the DFW market.

There are two types of people those who will fly with mogas and those who wont. You do not need much motivation to talk yourself out of it. If saving $3 soon to be $4 per gallon is not enough motivation then go for it.

It has been posted over and over again that there are many sources of auto gas without E. E is added at the pump so if you find any 55 gallon can available for $10 from craigslist and then get a jobber to fill it, just ask him not to put the E in it. You will have mogas. 320s take 80 octane so you do not even need to ask for premium. Most stations that sell E in their gas also have pure premium so you could pay $.30 more per gallon and get the 93 octane.

you can also get it at any boat Marena as E is not good for boat engines. So I guess I just figure if someone says something like "there are only 3 stations" in the whole darn state that sell mogas, after all that is posted in this and many other mogas threads, I have to come to conclusion you made up your mind and you are one of those other guys. Good luck with your choice.

your attitude about it not being worth pouring gas cans into the wings....Cessna that is your decision so why ask? tractor supply will sell you a gas tank for $400 with a 12V pump and make it every bit as easy to haul from 30-150 gallons of gas in a trunk, van or Truck bed and the payback will be about 75-300 gallons of mogas. With this setup you do not even need a jobber to deliver it to you, you can go to the wholesale distribution and pick it up. It is so dead simple I just have no time or patience for those who just lack the basic motivation to check it out.

So no I am not condescending as much as just tired and bored with all the folks who apparently need permission to not buy mogas so they stack a bunch of stupid obsticals, mostly imaginary, in their own way. It matters not to me what you fly in.