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 (archive)]

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).