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Dan,
the problem I experienced was with Amoco 93 octane unleaded.....but I have to blame the contamination, not the fuel.
I decided on using Amoco HT because of evaluating several fuels. I tested Exxon, Shell, Texaco, Citco, HT & 87 octane un-leaded fuels for alcohol and water retention. placing the fuel in baby food bottles with measured amounts of water; shake, and let settle. In all cases the fuel mixed with the water and formed a miscable layer of about 1/4 inch thick....slowly separating into the fuel and water ....all, that is ( including the Aviation 100LL, except Amoco 93 octane Ultimate fuel.) The Amoco Ultimate immediately separated into fuel and water, with no uptake of the water.
I further tested all the fuels with fuel cap gaskets for swell. All gasket samples did swell after a couple of days immersed in the fuel...but the Amoco Ultimate sample had the least amount of swell.
The third test I did was evaporation residue tests of the same fuels. Amoco ultimate left no residue! All others, including the Aviation 100LL left various amounts of residue ( varnish).
All this made sense to me that the Amoco Ultimate was the better fuel.....even tho I did not need 93 octane.....
This testing was done in about 1983; having read about water testing in EAA publications. I used Amoco Ultimate in all my autos, and when the STC from EAA was available, in the Ercoupe. I used Amoco Ultimate in the Ercoupe until 1996, when, after a period of limited flight, and lots of sitting...and the smelly fuel I put in the tanks.. I experienced the Algae problem.
I still prefer it for my autos, even tho many suggest the use of 93 Octane is not an economical way to go in autos that only require 87. I feel the electronic ignition systems in current autos that allow automatic advance of the timing through the use of a knock sensor controls makes for more efficient combustion...allowing benefits from the higher octane fuel. I may not be correct in this... :)..
I do think the very low/non existant varnish from the ultimate to be a benefit....However, after the Amoco/BP merger, I wonder if we still have the same clean fuel. BP claims they do, but I have not tested any fuels recently.
Harry Francis
N93530
Elliston, VA
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