85 octane gas May 06, 2006, 12:26:37 pm Yahoo Message Number: 66398Just a note on 85 octane gas – if you live and/or travel at elevations below 5000-6000 feet, you'll probably never see a gas pump labeled "85 octane", but this rating is commonly available (and sold as "regular") in Wyoming and Colorado, and in some parts of Utah, Montana and Idaho.As I understand it, the compression ratio of the V-10 engine requires 87 octane gas; using a lower octane can cause "pinging" (and engine overheating), i.e., the lower octane gas ignites too early in the cylinders. Theoretically, one *should* be able to use 85 octane gas in the V-10 at higher elevations because the air pressure at those altitudes is lower, and so is the pressure within the cylinders. This lower cylinder pressure reduces the compression ratio of the engine, so a fill-up with 85 *shouldn't* cause pinging and overheating. (Again, theoretically….)However, I tried to cheap out on 85 in my 2003 once in Colorado; never again – theory and reality don't necessarily mesh. My rig did *not* like what was on the menu, and showed her distaste by pinging loudly. I ran half a tank of 85, then filled with 91 (89 wasn't available) to even out the octane. On subsequent fills, I used 87 where I could find it, and 89 (pricey overkill, but no pinging) if I couldn't; no more pinging.Maybe some folks can run successfully on 85 octane in higher elevations, but one experiment was enough for me; I always fill with at least 87, from sea level on up to whatever. Maybe some "high country" folks might comment on their experiences with 85 octane.Joan
Re: 85 octane gas Reply #1 – May 07, 2006, 05:59:17 pm Yahoo Message Number: 66453QuoteAs I understand it, the compression ratio of the V-10 engine requires 87 octane gas; using a lower octane can cause "pinging" (and engine overheating), i.e., the lower octane gas ignites too early in the cylinders. Theoretically, one *should* be able to use 85 octane gas in the V-10 at higher elevations because the air pressure at those altitudes is lower, and so is the pressure within the cylinders. This lower cylinder pressure reduces the compression ratio of the engine, so a fill-up with 85 *shouldn't* cause pinging and overheating. (Again, theoretically….)However, I tried to cheap out on 85 in my 2003 once in Colorado; never again – theory and reality don't necessarily mesh. My rig did *not* like what was on the menu, and showed her distaste by pinging loudly. I ran half a tank of 85, then filled with 91 (89 wasn't available) to even out the octane. On subsequent fills, I used 87 where I could find it, and 89 (pricey overkill, but no pinging) if I couldn't; no more pinging.Maybe some folks can run successfully on 85 octane in higher elevations, but one experiment was enough for me; I always fill with at least 87, from sea level on up to whatever. Maybe some "high country" folks might comment on their experiences with 85 octane. Joan Hi Joan,We've been out to Wyoming/Montana with our LD several times and always use the 85 octane gas in our 2003 rig. Never experienced any pinging. Added bonus is that we actually get better MPG while driving in those areas with the 85 octane gas. I did read in the Ford manual that they don't endorse using 85 octane fuel. Its my belief that with the electronic brains in these vehicles, the computer can compensate for altitude, load conditions, and fuel differences. Don't understand why you had a problem other than the possibility that you got a bad load of gas.While on this subject, just a reminder to all about the wisdom checking your air filter. When driving at high speed and lots of miles, I've found significant build up of debris clogging the filter; mostly dead insects. This can hurt your mileage.Steve K.
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Topic: 85 octane gas (Read 3 times)
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