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  #11  
Old 02-05-2021, 01:07 PM
Bcone1381 Bcone1381 is offline
 
Join Date: Dec 2015
Location: Chelsea, MI
Posts: 98
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Gasoline boils at a relatively low temperature. If the gas boils problems result. Pumps move liquid, not vapors for example.

Car gas standards vary from state to state, but 100LL manufactured to standards that control things like its boiling point. More research is needed to know what that point is, but 150F for autos was one result the trusted internet spit out. Winter blend fuels will have a different (lower) boiling point than summer blends.

So keep things that might be a heat sink like the electric fuel pump, and gascolator cool and out of the engine compartment to help make an installation tolerate auto-fuel. Also keep your fuel line lengths as short as possible and away from exhaust. A 3/8" DIA line will move fuel faster over its length than a 1/2" line. You might also insulate your fuel lines and your fuel totalizer hardware, and place a cooling shroud on your engine driven fuel pump.

Maybe this is the reason why one person's aircraft burns auto fuel with no problem yet another one has issues. So, its more to it than compression ratio to determine rubber compounds.
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  #12  
Old 02-05-2021, 01:27 PM
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airguy airguy is offline
 
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Location: Garden City, Tx
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Quote:
Originally Posted by Bcone1381 View Post
Maybe this is the reason why one person's aircraft burns auto fuel with no problem yet another one has issues.
Absolutely true - and I'm happy to share the path that I took to enlightenment and running 91E10 - but that really should be another thread.
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  #13  
Old 02-05-2021, 02:20 PM
BH1166 BH1166 is offline
 
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 708
Default Just say no

To 100LL..... recently running pump gas 80% of the time, 93 octane alcohol free in my 1991 O320 D1A 160 hp. I convert my fuel cost savings to flying faster burning more fuel. AMERICA
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  #14  
Old 02-05-2021, 02:53 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 2,222
Default 100LL

Please bring on the 100 unleaded av gas. Cant wait for the lower maintenance (no plug fouling, less slug in oil, etc).
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #15  
Old 01-29-2022, 07:20 AM
David Z David Z is offline
 
Join Date: Aug 2010
Location: Thunder Bay Ontario
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Browsing the internet yesterday, I stumbled across this document from Lycoming. SL270 titled "Extended Maintenance Intervals for Spark-Ignited Engines Operated on Unleaded Fuels".

Seems Lycoming is happy to recommend doubling the oil change hour internal when running entirely on unleaded fuel. Still need to change the filter at 50hrs, but the oil can keep going.

Yes G100ul costs more. Does that offset the reduced cost of oil changes? I suppose it's very specific to each engine and how much fuel and oil it consumes. An oil guzzling O-235 will be a different story than a clean TIO-540 chugging back 20gph.
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  #16  
Old 05-13-2022, 04:06 AM
hoyden hoyden is offline
 
Join Date: Jul 2011
Location: Minneapolis, MN
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My foray into running 91 non-ox in my IO-360 ended after about 15 minutes. I had 100 LL in the left tank and mogas in the right. I took off with 100 LL and tried cruising on mogas. The first thing I noticed was a drop in fuel pressure from 24 psi to 7. I turned on the electric fuel pump. This happened 4 times. During the time in between loss of fuel pressure I tried leaning. The engine did not seem to lean as well. EGT was around 1300 and CHT 290-320.

I returned home and drained the right tank. Then I flew to a local airport to fill up with 100 LL. I did verify the right tank filled with 18 gallons.

My mechanical fuel pump is about 10 years old. It pumps 100 LL at 24 psi. Most of the time the pressure is steady but occasionally there are brief fluctuations to as low as 18 psi. I may replace the pump but I am hesitant to try the mogas experiment again.
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  #17  
Old 05-13-2022, 04:44 AM
wilddog wilddog is online now
 
Join Date: Feb 2008
Location: va.
Posts: 751
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Quote:
Originally Posted by David Z View Post
Browsing the internet yesterday, I stumbled across this document from Lycoming. SL270 titled "Extended Maintenance Intervals for Spark-Ignited Engines Operated on Unleaded Fuels".

Seems Lycoming is happy to recommend doubling the oil change hour internal when running entirely on unleaded fuel. Still need to change the filter at 50hrs, but the oil can keep going.

Yes G100ul costs more. Does that offset the reduced cost of oil changes? I suppose it's very specific to each engine and how much fuel and oil it consumes. An oil guzzling O-235 will be a different story than a clean TIO-540 chugging back 20gph.
Lycoming still recommended oil change at four mos.
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  #18  
Old 05-13-2022, 04:46 AM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
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Quote:
Originally Posted by hoyden View Post
... I may replace the pump but I am hesitant to try the mogas experiment again.
Sounds like you experienced some vapor lock. I'd have a look at the tubing between the tank and your fuel pump. There may be a place where the flow is constrained, and it's causing the fuel to change state from liquid to gas.
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Last edited by rv8ch : 05-13-2022 at 04:48 AM.
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  #19  
Old 05-16-2022, 06:23 PM
hoyden hoyden is offline
 
Join Date: Jul 2011
Location: Minneapolis, MN
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Quote:
Originally Posted by rv8ch View Post
Sounds like you experienced some vapor lock. I'd have a look at the tubing between the tank and your fuel pump. There may be a place where the flow is constrained, and it's causing the fuel to change state from liquid to gas.
I was surprised to have vapor lock while in cruise. I plan to measure fuel flow from the left and right tanks using the boost pump to see if they differ.
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  #20  
Old 05-17-2022, 10:55 AM
Bcone1381 Bcone1381 is offline
 
Join Date: Dec 2015
Location: Chelsea, MI
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Quote:
Originally Posted by hoyden View Post
I was surprised to have vapor lock while in cruise. I plan to measure fuel flow from the left and right tanks using the boost pump to see if they differ.
Reach out to Airguy, posted on Feb 5th. I'd be interested in hearing what he has to say.

As you look over your installation think "Hot fuel. Look where the fuel passes and it distance between warmth or things that touch fuel might get warm. As the fuel heats up it will vaporize at some point (or the fuel pressure will drop which lowers the boiling point) So a 90 degree AN fitting in a fuel line might be a weakish spot.
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