Is Costco 85 Octane OK For My Gen lll Prius

85 will be just fine for higher elevations. Big hills and mountains.

 

As stated by Retired4999, 85 octane is common in higher altitudes (equivalent to 87 octane at sea level)

 

Go with it. Prii can take the 85.
Not like the Smart car needs 91. :~((

 

I have used 85 Octane everywhere it has been available (MT, WY, CO, UT for my travels, in Prius and four previous non-hybrids) for over thirty years, and have never had a problem with it. The two oldest cars had enough carbon buildup to have ping problems on 87 octane at elevations below about 1000 feet, but had no problems with 85 at the 5000+ elevations where I found it available.

It seemed that 85 was traditionally not sold within normal fuel tank range of lower elevations where it could be a problem. But with the longer fuel range of modern cars, it is something to think about when traveling far downhill immediately have fueling up.

 

My understanding is that 85 octane at 4500 feet is like 87 octane at sea level. If you get too close to sea level on that same tank of gas, there would be issues.

 

Octane is fine but the gas is isn't.

 

I'm curious if you noted this, but do you know what kind of gas mileage you would have gotten with the TDI and with the Prius on that same trip?

 

The kids can start making their own biodiesel.

 

I don't own a Prius, but my TSX is designed for 91 octane and the manual states it can run on as low as 87. That said, I filled up with 85 when in MT. Highway cruising is easy and doesn't require a high octane. Elevation further reduces the need for higher octanes.

At about half a tank left on the 85 octane fuel, I came upon Fourth of July pass where I would sustain a long hill climb, and eventually end up at a low elevation in Portland. Hill climbs, acceleration, lower elevation all require higher octane. Basically, anytime more air is being drawn into the engine due to higher air density or pressing the accelerator harder.

I filled up with premium fuel at the bottom of the pass so that I could bring up my octane for the hill climb and eventual decent to 100ft elevation.

To answer your question, I would fill up with 85 as long as I was planning to stay at high elevation for the duration of the fuel in the tank.

Another trick I sometimes do is to pump about 50% of my fill with premium and then fill the rest with regular. This is often cheaper than using mid-grade, which in Oregon/Washington is 60% regular and 40% premium. The very frugal will also note that pumping regular fuel after the premium will ensure all of the premium you paid for is pumped out of the hose.

 

My mechanic said Costco gas was subpar. No clue if that's accurate.

 

He said that because Costco isn't a top tier fuel retailer.(BP is likely the supplier for Costco) That said, the only thing special about top tier fuel is extra detergents that are used to keep the fuel system clean. The gov't sets the minimum level of detergents, and top tier fuels use more. I don't see a need for top tier because I've never had an issue with my fuel system in the hundreds of thousands of miles I've traveled on Arco gas. You can also purchase detergents and add them to your fuel tank periodically if you're concerned about not having adequate detergent in the fuel.

 

BP is listed, yet it's not a top tier if Costco uses it as the supplier?

 

The refineries sell different versions of their gas, some with a certain level of detergents, some with a lower level. Not all gas from the same refinery will be rated top tier, which includes the gas they sell to third party retailers.

In other words, they keep the good stuff for their own stations.

 

That likely varies from market to market. In most areas, a very few refineries supply nearly all the many brands.

 

thats great thanks for the info!