85 Octane at high altitudes?

[lewsterr]

I am moving from Maryland to Colorado and, of course, taking my 2008 CRV EX 4wd. Their regular grade gasoline in the Denver area is 85 octane (87 is mid-grade). I was told that, with the higher altitude and thinner air, it's not necessary to use 87 octane. Does this hold true with the CRV? Will it run well out there with 85 octane? If so, will this void the warranty?

[tsmithvt]

I am moving from Maryland to Colorado and, of course, taking my 2008 CRV EX 4wd. Their regular grade gasoline in the Denver area is 85 octane (87 is mid-grade). I was told that, with the higher altitude and thinner air, it's not necessary to use 87 octane. Does this hold true with the CRV? Will it run well out there with 85 octane? If so, will this void the warranty?

Your V's ECU will automatically compensate for the reduced oxygen content in the air at higher altitudes (F/A ratio). There is also some truth to the idea that the reduced air/oxygen density reduces the tendency of fuel to preignite under compression but it is not a dramatic effect.

Your owner's manual, however, is pretty specific about fuel octane requirements and it does not make any exception for altitude. I would be careful about using 85 octane fuel. If you detect any preignition (knocking) at all, immediately discontinue its use and go back to 87 octane. If your V were to need engine work later in its life and piston head or skirt damage was detected, your warranty (5 years/60,000 miles) would be void.

Try it, but carefully.:)

[08ColoCRV]

Generalizations are always dangerous, but I'll say it anyway:

Most people around here burn the 85 octane in their cars without giving it a second thought. Somebody gave me a very technical explanation of why it was OK, but I've long since forgotten the details. Heck, I can't even remember who the person was, but I remember it was someone who ought to know.

The basic principle was that if your car was designed to run on the lowest octane gas available at sea-level locations, it would run just fine on the lowest octane gas available at mile-high locations.

Hopefully somebody will jump in here with a more technical explanation!

Best regards and welcome to the area.

Rod
Loveland, Colorado (5,016' official elevation at the airport--KFNL)

[tsmithvt]

A naturally aspirated, combustion engine draws in less air/oxygen during the intake stroke because of the reduced density of the air at higher altitudes. This reduces the absolute compression in the cylinder and naturally deters preignition (knock).

[08ColoCRV]

There you go...

Tsmithvt provided the technical answer I was hoping for!

Run the 85 octane and enjoy your CR-V! :D

Best regards,

Rod

[Badgerland]

I used it (85) last August when I was cruising Mt Evans and some of the other high passes and my CRV performed great. When I made the trek home I filled up at Copper Mountain and got 435 miles out of that tank going 65mph. Not too shabby...30.1 mpg that tank. Yea I know....all down hill to Kansas!