3.4 5ZFE - 85 vs 87 octane?

Originally from east coast, where I've generally filled up with 87 octane. I've noticed Denver/CO has 85/87/91? I've been filling up with 87 since arriving, but what's everyone filling up with? 85/87?

 

At that elevation you can probably get away with 85, thats why its usually only offered at higher elevations

Closer to sea level you won't see anything under 87

 

If you're at elevation as Denver is the air is thin enough to use 85 where 87 is called for in other climates

 

Not every place in Colorado has 85, but yes, most do have 85/87/91. I've always filled up with 87 and I'd recommend you run a few tanks on each and see which you prefer. I'm at about 6,000 feet.

 

Running lower octane gasoline than what the manufacturer requires at high elevation works great for carbureted vehicles and people keep thinking that it's the same for fuel-injected vehicles.

FWIW: My wife's 2000 Wrangler TJ takes 87. I did not know this for a few years with her, her dad says to always use the lower octane gasoline, 85, living at 7000' for the Jeep as it will start and run better, etc. It stumbled on startup and did not run smoothly. I did plug, cap, wires, fuel, and air filters, and both O2 sensors. The condition did not improve. I recorded what I did in the owner's manual and read that Jeep says 87 gasoline. It was close enough to empty so I filled it with 87 and then drove it for an hour. Ever since then the Jeep starts right up, smoother power delivery and the tank trip mileage has gone up.
Her dad hates to be wrong, he worked in the Pentagon for 30 years and knows an unnaturally high amount of facts. He now fills up with what the manufacturer says for octane on his FI vehicles and says he get better results.

Your results may vary.

 

Using higher octane than recommended does not seem to enhance anything for many FI vehicles I have driven at elevation, even the pump 102+ octane Shell gasoline in Phoenix Az in the mid 1990s when I was auto crossing my '84 Rabbit GTI when I lived in Flagstaff.
I have heard that the higher octane gasoline burns "cooler", but I got no proof.

 

Only advantage to higher octane is if you're running forced induction, on a naturally aspirated engine it's just spending more $ than necessary. Although some FI vehicles can run lower octane because the ECU will adjust for it. Not on these trucks though.

This thread is gonna turn into a 87 vs 91 debate now, get ready

 

GO!

 

85 though I’ll switch after new tune. I’ve always ran 85 even when we lived at 9200 feet. My Jeep went from a 2-barrel carb to EFI and in both cases ran 85 without issue.

Just comes down to fuel/air mixture and point of combustion.

 

Knock correction on modern EFI vehicles means you can run about any octane gas found anywhere in the states.

Knock correction on Toyota vehicles will keep the timing at maximum advance given the fuel octane level within programming limitations.

On my 5vz I noticed a very narrow range of knock correction. There was little to no base timing advance from 87 to 91. 85 was common to still make noise on hot summer days. I ran 85 in the winter and 87 in the summer until I was supercharged. This was on all my 5vz powered vehicles (over 7).

My early (00)Tundra 2uz would have noticeable running differences in octane level. Base timing would advance with each increase in octane level. None of the octane levels had drivability issues. I would run 91 whenever I could as I noted the best fuel mileage and power. Conversely my 03 4runner v8, 05 Tundra didn't net any value change over 87. 85 in both of those had a small decrease in fuel mileage, almost not noticeable. Ran them both at 85 almost every tank.

The 5.7 Tundra doesn't like 85. When hot I can get a tiny bit of audible noise and the fuel mileage drop is about 1mpg (13 to 12). Haven't got around to trying 91, once I stop using the remote start so much I might.


TLDR, run them all. If you get ping, bump up. If 91 nets no benefit drop down to 87 or even lower. Running "Top Tier" fuels will likely be your biggest drivability difference that you'll notice.