Sea Level to Mile High

oldsmanw31 · #1 (**permalink**) 02-18-07, 04:31 PM

I have a 98 Seville and I was thinking about moving to Denver. I had heard at one time that they run a different blend of gasoline in the higher altitudes. Is there anything I should do to prepare the car for that high of an altitude?

thu · #2 (**permalink**) 02-18-07, 06:51 PM

No preparations are necessary. You'll find that the octane of the different grades of gasoline is going to be lower than you will find at lower altitudes. However, you'll probably never need more than mid-grade due to the lower cylinder pressures owing to the higher altitude.

You'll also notice less power, but economy will remain essentially unchanged.

Why are you thinking of moving to my neck of the woods?

**Ranger** · #3 (**permalink**) 02-19-07, 01:23 AM

Thu is right. The PCM and engine sensors will make any adjustments necessary.

Rafter S Tom · #4 (**permalink**) 02-19-07, 01:04 PM

Very important at higher altitudes to keep the air filter clean, due to thinner air. This happened to me on the move to Albuquerque.

NickyE3 · #5 (**permalink**) 02-19-07, 01:53 PM

last time i was up there they had 93 octane at the pumps

thu · #6 (**permalink**) 02-19-07, 02:58 PM

Yah, I noticed that sometimes the premium pumps at a few stations had 93. However, by and large, premium tops out at 91.

I wonder, if in Alberquerque, they sell 93, because the altitude falls off rapidly in the immediate surrounding area? I don't have my aviation charts handy, so I cannot confirm this. Perhaps they don't like stocking two different kinds of premium, so some gas station chains just ship 93 everywhere.

I've tried testing different grades of gasoline at my altitude (between 5000 and 7200 feet) - no MPG difference whatsoever.

At 6,000 feet, normally aspirated engines produce only 75% of the power they normally would at sea-level. Hence, the reduced octane requirement.

Rafter S Tom · #7 (**permalink**) 02-19-07, 03:08 PM

Gas stations in Albuquerque generally sell 86, 88, and 91 octane. We're at about 5000 feet elevation, and it doesn't fall off that much in surrounding areas (maybe 1000 feet), and goes to 7500+ feet in the mountain areas.

The air filter problem I referred to was a number of years ago, and NOT IN A CADILLAC, so no automatic sensors on air/fuel. Hope that clears things up.