uphill, with a/c, high altitude, & a trailer: use premium gas?

Temporarily upping the octane for climbing mountains/hills wouldn't be a bad idea at all... it'l help reduce the pinging that can happen when the engine is under load at altitude. Run 87 the rest of the time though since higher octane doesn't really do anything for normal driving in a 4.0L Jeep engine. :)

Jerry

Of course driving on level ground at higher altitudes allows a lower octane to be used. Driving uphill from lower altitudes doesn't give that same ability.

Jerry

thats interesting. in north carolina @ 80 ft. elevation the "regular" unleaded is 87 octane. here in montana from 3500 to 11,000 feet the "regular" unleaded is 85.5. i often wondered why it was different out here, thanks for the information!

to answer the original question i had no problems with my rubicon at 11,000 feet. i wasnt towing anything but was climbing really steep grades with no noticeable loss in power.

I had no problems around/near 14,000 feet with regular. Purred like a kitten.

The owner's manual doesn't reccomend the lower octane for late model engines. Something about the various sensors not givng the computer the correct info. Not sure which one might be involved, the O2 sensor should be happy no matter what. Might be the MAF sensor.

As a side note: the lower octane should have a slightly higher BTU per pound c>>Subject: Re: uphill, with a/c, high altitude, & a trailer: use premium gas?

Strictly anecdotal, but I would seriously consider going up one grade because of a simple test. The older 4.0 MPI included a knock sensor, which essentially retards the spark when it signals the computer of a knock. If I leave Colorado Springs and head over to the western slope over some 10-11,000 foot passes I can see a definite difference in how I pull the long grades. That indicates to me that the computer is detecting some amount of ping and retarding the timing to some degree resulting in a little less power with the 85 octane - but it's enough to have me down shifting pretty often. Of course, having 3.07 diffs doesn't help in the least, but I see a definite difference. One grade in particular shows a consistant difference that grabs my attention: the pull up the west approach to Eisenhower tunnel. There are places where I will wind up in 3rd to hold speed with regular (85 octane) while using the midgrade (87) I pull the whole climb without lugging in 4th (forget 5th if there is a hill in sight once you get above about 3000 feet).

Now, the higher octane does not provide any more energy, it simply allows the engine to work a little harder without pinging. The only way I'm seeing better power with the higher octane pretty much has to be the knock sensor effect. I think that some owners manuals do, in fact, suggest using the higher octane for towing and moutainous terraine - at least the 88 manual does.

Handywired proclaimed:

You can probably lower the octane. Less chance of pinging at high altitude--actually ran into some "regular" this last trip that was only 85 octane. However, I've noticed a bit more ping with "bush gas" and regular, so tend to use midgrade on cross country trips.

If you can climb hills at low altitude with that kind of load, and it doesn't ping, you won't have a problem at high altitude. Use the same octane fuel you use at low altitude.

Don't need any fuel to go downhill!!