| [GMCnet] Fuel for high altitudes [message #96991] |
Mon, 23 August 2010 23:04  |
Gerald Work
Messages: 102
Registered: June 2010
Karma:
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Senior Member |
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I have followed the various posts on fuel quality with interest. We are now nearing 10,000 miles on our cross country adventure and have lots of first hand experience with fuels of all qualities from access the NA continent. I think most already know that fuel mileage goes down by more than the percentage of alcohol in the fuel. 10% alcohol means about a 15% reduction in mileage, etc. Power also goes down by more than the % of alcohol in the fuel. Based on what we have experienced, I can't even imagine how anyone can use that 85% alcohol junk.
We have observed that at high altitudes our coach performs much better running on "premium" fuel even though we do not ping on 87 octane fuel. In the Rocky Mountain region the 87 octane fuel pumps say "at least, or up to, 10% alcohol". The premium pumps do not indicate any alcohol. The premium has a very different smell from the alcohol junk. As we climb grades in the 6000 to 10000 foot range we do not find we need to turn on the electric fuel pump of we have premium fuel in the tank. If we have 10% or more alcohol the coach will not go up the hill unless the electric fuel pump is on no matter what the temp. I don't think it is "just" alcohol boils at low temps resulting in vapor in the lines. I think more is going on.
What ever the difference is between the 87 and the 92/93 octane fuel, the coach will struggle up the hill with the former and boogy up the hill with the latter. That has been true all over the country. Again, it has nothing to do with audible pinging, the coach simply runs better with the premium stuff at high altitude while it runs equally well on 87 octane at less than 4000 feet no matter the % alcohol in the 87 stuff.
I will leave it to the fuel experts to explain why, but I will not again climb high mountains running anything other than premium fuel. On level ground at high altitudes or at altitudes less than 4000 feet 87 octane is just fine no matter how much alcohol (up to 10%, we have never tried more than 10%). Up hill over 4000 feet, premium it will be.
Hope this helps. For those who like the details, this is a 78 Royale with a strong 455, 3.5 gearing, no tow, 12,400 pounds all up, well balanced side to side and front to back, Toyo 225/75 16 rag wall load range E tires, 8.5 mpg over all, etc.
Jerry Work, Kerby, OR, now in Ennis, MT, a really pretty place.
Sent from my iPad
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