Gas for Ford V-10

You may note that those that aren't real experienced at "real" mountain driving (ie over 5000 ft) think that 87 is "required".
Well, 85 at real elevation preforms like 87 at sea-level. That's why "regular" is 85 at elevation and 87 at sealevel

Here is the best advice, RTFM (read the ford manual) they know the engine and it's requirements better then any "internet" "x-pert"

I stick with 87, always.

I just drove my Ford V-10 from Virginia to Washington - 2750 miles - and used either 87 or 85 octane the entire way. No pinging, no issues at all.

There's a great RV park in Livingston, MT named Yellowstones' Edge RV Park. It's right on the Yellowstone River is is 34 miles north of the park entrance.

engines that need 87 octane at sea level will run just fine on 85 octane at altitude, unless said engine is turbocharged, in which case, you need to stick to 87.

My V0 runs fine on 85 octane in WY. I use it in my MH and also my V10 PU. I ran it in both V10 PUs. One now has 45, 000 miles and the other about 110, 000 miles. I've towed stock trailers loaded down pretty heavy without any problems. If you feel uncomfortable with 85 octane pay a dime more a gallon and use 87.

Stick to what you know. 87

I'm not a expert, but I did stay in our motorhome last night, so here goes.

Octane, is used to control detonation in high compression engines. It serves to slow the combustion of the fuel in the high compression engine. It can eliminate the knock or ping heard during heavy/hard acceleration. That knock or ping is detonation, it can be very harmful to a engine if it's heavy or continuous. The most common result of to much detonation is a hole in the piston. Not good. So we want to control detonation, hence the higher octane.

That said, it serves to reason that unnecessarily high octane will result in lower performance, and less miles per gallon. If your engine doesn't need it ie: most engines mass produced today. You are not only wasting your money on the higher price, you are also losing miles per gallon. Not real noticeable but real facts none the less. It does you no good unless you need it to control detonation.

That said, the ethanol that they are putting in our fuel today is supposed to serve two purposes. The claim that it reduces pollution is the main purpose. The other purpose is to increase the octane rating of gasoline. It doesn't burn as good or as fast, nor does it have as much heat as gasoline, so it serves the purpose of raising the octane rating very well. With those facts in mind, how can it actually reduce pollution when it requires more fuel to equal the heat output/power of pure gasoline?
Reformulated gasoline that has been oxygenated with ethanol is the only "BIO Blend" of gasoline that I know of. Ethanol is not good for engines. It is hard on the rubber parts, attracts water and doesn't store well. As you might be able to tell I am not a fan of ethanol in our gasoline. I know it does quite a bit of harm particularly to small engines. I use the higher (91) octane (the only gasoline without ethanol available around here) for all my small engines and boats to avoid the problems I have experienced with ethanol blended fuel.

All of that said, the lower octane (85) fuel you see in the mountains is because of the altitude. Thinner air with less oxygen doesn't let the fuel burn as efficiently so you need a more volatile fuel to get the same performance (power and MPG) as at lower elevations.
Use the lower octane if your going up to the high country, higher octane for the low lands.

I would stay with what it calls for 87.

Octane is a measurement of Anti-knock capability of the fuel. If you burn 87 octane fine in California, then you'll most likely do fine with 85 in the mountain states. 85 is considered "regular" unleaded at higher altitudes due to the lower atmospheric pressure. 85 octane at altitude is similar to 87 octane at sea level.

Octane has nothing to do with the energy content of the fuel, but it's resistance to preignition detonation (knocking). Try a tank of 85 octane. If you don't hear pinging when under load, you'll be fine. If you do hear pinging, then switch to higher octane fuel and pay the higher price.

Don't buy the super cheap bio blend. The alcohol destroys all the rubber seals. Buy no lower than "regular" 87.

Jose