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  #1  
Old 03-04-2011, 08:13 AM
prkaye prkaye is offline
 
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Location: Ottawa, Ontario, Canada
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Default gasoline detergent

My engine manufacturer (Aerosport Power) has said that i can use a 91 Octane auto fuel in my O-320 as long as it does not contain ethanol or methanol.

Apparently the 91-octane gas sold by Petro-Canada does not contain ethanol (although I can't find any information about possible methanol content). But it does say it contains Tactrol?, a proprietary deposit control additive, sometimes called a gasoline detergent, that is designed to keep fuel systems clean. Two questions

1) Is there any reason to believe this detergent additive would make the fuel unsafe for aviation use?

2) Is there any issue with mixing 100LL with an auto-fuel like this?
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  #2  
Old 03-04-2011, 10:05 AM
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rocketbob rocketbob is offline
 
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Phil you shouldn't have any problems. I'm highly certain the mogas I use has the same or similar detergents detergents.

I have always thought that 100LL is just awful fuel. The lead contaminates your oil, forms sludge deposits particularly in the crank, and prevents us from being able to use more modern synthetic oils. Lead spark plug fouling and huge lead deposits on the faces of pistons are common.

With my hodges fuel volatility tester I've only found a marginal difference in safe vapor pressures. In the real world, as others have posted here, you can get vapor lock with 100LL although its much less likely. The main root cause of this is the nature of how our yesteryear fuel systems are designed. Since the pumps draw fuel from the tanks, they work just like the tester does in causing vapor to form...by sucking on the fuel line. If you pump gas from the tanks, under pressure, this will never be a problem. This is why the fuel system in my rocket uses pumps at the tanks which negates the need for a fuel selector.

In your case, as in the case with my flying RV, it doesn't have this type of pump setup, so the best insurance on warmer days to prevent vapor lock is to run the boost pump all the time. I have climbed many times on 95 degree OAT days to altitude with the boost pump on, and have had no problems. But I found this out inadvertently one day when I forgot to turn the boost pump on, and was climbing out and started to get a rough running engine. Turning on the boost pump instantly took care of the rough running.

Another area when I do have had an occasional problem is with a quick turnaround on a hot day. Since fuel is sitting in the carburetor bowl boiling, it will be difficult to start and once it does start, the engine will want to quit taxiing out. The easy cure for this is to open the oil door after landing to mitigate heat soaking the engine compartment. Seems to work for me.

The other time I have had vapor issues is when taxiing out on a hot day, and have been held by a controller or traffic with an extended period of idling. Running the power up to 1200-1500 rpm will mitigate this problem by forcing that nice fan up front to cool things.

As far as octane goes, everyone seems to say only use premium fuel. I have not found regular 87 octane to be detrimental in any way.

On our airpark we have a 500gal tank I fill up from. On a trip to NC last November I had difficulties starting and thats the only time in almost ten years I've had that problem, and I attribute it to bad gas. Our tank was running low and the fuel in it was a couple of months old.

You certainly can mix the fuels as I have to all the time on trips where mogas is unavailable.
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  #3  
Old 03-04-2011, 10:47 AM
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rv8bldr rv8bldr is offline
 
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Quote:
Originally Posted by rocketbob View Post
Stuff deleted...

...and prevents us from being able to use more modern synthetic oils.
Hey Bob

Could you expand upon this statement a little? What about semi-synthetic oils?

Thanks
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  #4  
Old 03-04-2011, 11:12 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by rocketbob View Post
...As far as octane goes, everyone seems to say only use premium fuel. I have not found regular 87 octane to be detrimental in any way...
Quote:
Originally Posted by lcnmrv8r View Post
... Fyi, I use 87 all the time with no issues. My fuel economy is slightly less with the 87 but not enough to offset the cost.
What compression ratios are your engines?
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  #5  
Old 03-04-2011, 11:20 AM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by N941WR View Post
What compression ratios are your engines?
for me, stock... 8.5:1
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N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
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  #6  
Old 03-04-2011, 11:22 AM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by rv8bldr View Post
Hey Bob

Could you expand upon this statement a little? What about semi-synthetic oils?

Thanks
I'm really talking about full synthetics. Like the old Mobil1 that got pulled years ago due to lead scavenging problems.
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Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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  #7  
Old 03-04-2011, 11:26 AM
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Auburntsts Auburntsts is offline
 
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Quote:
Could you expand upon this statement a little? What about semi-synthetic oils?
The problem with synthetic oils is they don't hold contaminants in suspension very well which leads to sludge build-up, among other bad things. Sludge build-up can lead to blocked oil passages, loss of oil distribution and then expensive engine repairs. This is why Mobil AV-1 was removed from the market. Not an issue in cars mainly because mogas burns much cleaner due to its formulation without lead.

Here's a good article on the subject out of SportAviation by Mike Busch: http://www.sportaviationonline.org/s...pm=2&u1=friend
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Last edited by Auburntsts : 03-04-2011 at 11:29 AM.
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  #8  
Old 03-04-2011, 02:46 PM
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Cadstat Cadstat is offline
 
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Default Synthetic OIL

I think full synthetics are still alive and well in the turbine market. Semi-synthetics are used in lead powered recips. Exxon is selling 'Elite' blended weight that is a semi-synthetic promising to bring some of the advantages of both worlds.
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  #9  
Old 03-04-2011, 03:04 PM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by Cadstat View Post
I think full synthetics are still alive and well in the turbine market.
Yep... no lead in Jet-A.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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  #10  
Old 03-04-2011, 09:07 PM
glenn654 glenn654 is offline
 
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Bob,
You happened to bring out the number one reason I won't use autogas its the problem of "old gas".

From my understanding, auto fuel begins to breakdown almost from the point of refining, whereas I have read that avgas can be stored and used safely up to 2 years and perhaps a little longer.

My airplane has sometimes sat for a couple of months and much longer when I did a panel rebuild years ago.

I just don't want to take the chance of having my fuel system loaded with crud because of old car gas and the safety problems that come with it.

Never a problem with avgas

YMMV,
Glenn Wilkinson
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