85 Octane

[John Mo]

Anybody run the cheap 85 octane gasoline found in the midwest? I have a 2008 V10 and was just wondering if I needed to stick with the 87 octane or if the cheap stuff is OK.

Thanks

[DandS]

Copied from owners manual of my v-10 : "Your vehicle is designed to use
“Regular” unleaded gasoline with
pump (R+M)/2 octane rating of 87.
We do not recommend the use of
gasolines labeled as “Regular” that
are sold with octane ratings of 86 or lower in high altitude areas."

That said, not sure if it would do damage or not, but I guess I would rather be safe than sorry !

[wa8yxm]

As I understand it you do not need as high an octane rating in higher altitudes.... That said, rig did not run well on 85.. You can always add a little premimum to the tank to bring it up (That is, in fact, how multi-octane pumps often do it, mix super premium with regular to get the rating you select)

[LVJ58]

I have on occasion used the lower octane fuel in our coach but generally pay more for the higher octane in those areas mentioned. Never noticed any appreciable difference in fuel mileage nor did I experience any pre-ignition knock from the engine. I agree though best to stick with the octane recommended by the engine manufacturer.

[Izzyblueye]

Quote:

Originally Posted by John Mo Anybody run the cheap 85 octane gasoline found in the midwest? I have a 2008 V10 and was just wondering if I needed to stick with the 87 octane or if the cheap stuff is OK. Thanks

Unless you can't get 87 what would be the advantage of running 85. I live in the Midwest and have never seen 85 octane fuel, with the exception of Sunoco.

[John Mo]

I stuck with the 87, figuring that was what was "recommended." But I did wonder if the engine electronics were advanced enough that the 85 would be OK and compensated for. Sounds like it would work, but not really a good idea. Thanks.

[Hikerdogs]

In Wisconsin the only 85 octane fuel I've seen is E85 (ethanol). It isn't recommended for vehicles that require 87 octane regular fuel. It's only supposed to be used in "Flex Fuel" (ethanol compatible) vehicles.

[John90XJ]

I did a trip through Utah and Nevada a couple months ago and followed the manufacturer's manual and filled the tank with 87 octane while in UT.

On a previous trips while driving the Jeep, and not the motorhome, I've done the 7-8,000 foot passes with the 85 in the tank and noticed no difference whatsoever.

I would have to guess the octane rating wouldn't make that big a difference but it doesn't seem to be worth the $5 in savings each fill-up to find out. I'd rather play it safe.

[two2go]

Altitude changes the burn characteristic of gasoline. I don't know the chemistry, but going higher allows octane to be reduced. All regular in most of Colo. is 85 octane and is fine for any engine that runs on regular 87 at lower altitudes, so save your money unless you really experience a problem. I saw 86 octane at a station that was about 3000', the first time I saw an intermediate octane. I had an Audi that required 89 per the manual, but it ran fine on 85 in Denver. The engine computer compensated although with a slight mileage and performance penalty. I have noticed when I take my tow'd to a lower altitude and still have a tank of 85 gas in it, I can sense a bit of knock and lower performance.

[RustyJC]

Higher altitude > lower air density > lower compression pressures > lower peak firing pressures = less horsepower, less torque with the result being reduced tendency for the air/fuel mixture to detonate (knock or ping).

The chemistry doesn't change at higher altitudes, just the engine operating characteristics.

Rusty

[Forest Grump]

Since octane is measured in a knock engine by altering the engines compression it would suggest that if the 85 octane is not knocking then it's use is fine. However if it knocks don't use it.

[Wizard]

I'm traveling around Wyoming and everywhere I've filled up the only thing available was 85. The FJ in Cheyenne was replacing fuel tank or something and was selling 93 at the 85 price at all pumps. I didn't seem to tell much difference running the 93. Still had to refill a few miles down the road.

[Dave G]

I have used it all the time in higher altitudes as it is sold as the regular gasoline. Have made many trips and never had any problems.

[BounderDan]

While in the Rockies I used the 85 octane a couple of times in the motorhome (Bounder with V-10) and the only difference I noticed was the price. also used it in our toad (Saturn Vue, 4 cylinder) and it also ran fine at altitude. However, upon returning home to near sea-level with a half tank of the 85 still in the Saturn the check engine light came on. Owners manual noted that this could be caused by low octane gas. Promptly filled up with 93 octane (mix should have come to about 89 octane) and after about 80 miles the light went out. It seems the lower octane stuff is okay if you stay at or above four or five thousand feet. The temperature and humidity was a lot better up there too. Danny