85 Octane in a 2.5X at 4500Ft+

[Ken Wampach]

I live in the Denver metro area. Around here, regular is only 85
octane. I understand that this is because the higher altitude
reduces the tendency to knock in a NON-TURBO engine. My
2004 Forester 2.5X calls for 87 Octane. I wanted to know if
this car can use 85 octane if driven exclusively above 4500 Ft.
I called the Subaru support number and they just quoted the
owner's manual and said it had to have 87 octane. I talked to
the service advisers at the dealership where I bought the car,
and they said I should not have any problems with 85 octane
from the major brands.

I have looked on the Web, and some manufactures say it is
OK to user lower octane at our altitude. According to
http://www.ethanolrfa.org/2000warr.pdf Nissan/Infinity said it
was OK to use 85 octane in their vehicles that specified
up to 91 octane, as long as they were driven above 4000 ft.

Has anyone seen a reliable answer for the NON-TURBO
Subaru 2.5 liter engines? If the answer was to say that 87
octane was mandatory, did they quote some real engineering
reasons, or are they just quoting the manual and playing it
safe? I would read that as an indication that they are not
willing to do some research which could save their
customers some money.

 

[David Ryeburn]

I live in the Denver metro area. Around here, regular is only 85
octane. I understand that this is because the higher altitude
reduces the tendency to knock in a NON-TURBO engine. My
2004 Forester 2.5X calls for 87 Octane. I wanted to know if
this car can use 85 octane if driven exclusively above 4500 Ft.
I called the Subaru support number and they just quoted the
owner's manual and said it had to have 87 octane. I talked to
the service advisers at the dealership where I bought the car,
and they said I should not have any problems with 85 octane
from the major brands.

I have looked on the Web, and some manufactures say it is
OK to user lower octane at our altitude. According to
http://www.ethanolrfa.org/2000warr.pdf Nissan/Infinity said it
was OK to use 85 octane in their vehicles that specified
up to 91 octane, as long as they were driven above 4000 ft.

Has anyone seen a reliable answer for the NON-TURBO
Subaru 2.5 liter engines? If the answer was to say that 87
octane was mandatory, did they quote some real engineering
reasons, or are they just quoting the manual and playing it
safe? I would read that as an indication that they are not
willing to do some research which could save their
customers some money.

It will run OK on 85 octane gas at your altitude, but it will run better
if you mix 85 and 89 octane gas in equal parts to give you the
equivalent of 87 octane. Then if you drive east to lower altitudes
you'll be safe too.

I have on a number of occasions driven two Subarus (first a 1988 GL
wagon, and later a 1997 Legacy Outback) from the Vancouver, BC, Canada
region where I live to the eastern USA, driving along I-90 most of the
way. As soon as we got to Montana the gas was lower octane. I generally
mixed grades as indicated above, except for a couple of occasions when
nothing but 85 octane gas was available, but I made sure to mix grades
at Rapid City, SD because by the time that tank was nearly empty we'd be
in eastern SD at much lower altitude and I wouldn't want to be burning
85 octane gas down at lower altitudes. And by then, the available
regular stuff was good old 87 octane gas.

Incidentally, I found major differences in gas mileage between national
brands (Exxon, Chevron, Texaco, Shell, Mobil, Amoco, etc.) and some of
the local brands when in the Rockies. A couple of the local brands were
at least 10% poorer in gas mileage, and the car seemed to be less peppy
when using them, too. This happened at various altitudes and was quite
consistent, over several trips, several years apart. I now have a short
list of brands I will not buy.

David, whose 240,000 km 1997 Legacy Outback is going east again shortly
after it completes a trip to the desert southwest this coming weekend

 

[Guest]

Ken Wampach wrote:

Has anyone seen a reliable answer for the NON-TURBO
Subaru 2.5 liter engines? If the answer was to say that 87

It didn't seem to bother the one I drove a few years ago.

 

[Paul]

Ken Wampach wrote:




It didn't seem to bother the one I drove a few years ago.

I live in denver as well and I use 85 octane. Seems to be going ok.
I bought my Subaru in Febuary of this year, and have used 85 since
owning it. One thing I have noticed (but maybe it's me) is that
diffrent brands of gas seem to be worse. I usually put gas in at
Costco (cheaper by 10c a gallon) and the car seems to get great
mileage. Conoco,Amoco are ok but Shell seemed to be the worst as far
as MPG. pAUL

 

[William S. Hubbard]

High altitude lowers the psi in the cylinders as the air is less dense. If
you use that at a lower altitude, it won't be pretty!

 

[Matt hotmail]

If the car says premium use it. You will get less than optimum results
using anything but the recommended. Also, lower octane ratings tend to
overwork the pistons...and if you want the car to last 200,000 or more I
would use the recommended. If you are only going to use the car for a
couple of years than it will be someone elses problem (and for those of you
without a conscience-you won't care).