Premium Gas

I have done it a few times when the station was out of regular. No noticeable change in MPG.

 

<div class='quotetop'>QUOTE(kdk84 @ Apr 28 2007, 07:51 PM) [snapback]431941[/snapback]</div>

1. "Premium" is not higher quality gas.
2. "Premium" has less caloric content, and all things being equal, will give you lower (insignificantly, probably) gas mileage.
3. It is currently illegal for a gas station to sell premium as being "higher quality" or better for your car (at least in CA - not sure if this is federal - Unocal 76 paid out quite a bit of money in a settlement a few years back).
4. It takes more energy (and creates more pollution) to make "premium" gasoline. Because of this, using Premium pollutes more than using regular.
5. A car like the Prius (and at least 90% of the cars on the road) get no advantage from using "Premium."
6. The only thing Premium is used for is to prevent pre-ignition in high-compression IC engines. You pay more money for your gas to burn slower. The gas doesn't make any car go faster, or get better mileage - it simply allows a high compression engine to operate most efficiently. If a given car doesn not require hi-octane gas, don't use it.

Did I miss anything?

Oh yeah... no, nobody will notice gas mileage improvement by using "Premium" in the Prius. (In case that wasn't obvious.)

 

<div class='quotetop'>QUOTE(kdk84 @ Apr 28 2007, 11:31 PM) [snapback]432029[/snapback]</div>

Only if the car is tuned to require the higher octane to keep it from detonating (pinging) due to agressive timing or high compression or both. Otherwise it is a waste to run higher octane than required by your specific engine and tuning profile.

 

I was wondering about this also and I'm glad you guys answered my question. I was reading in the manual and they say that the compression ratio is 13 to one and I was wondering how this would ever run on regular gas. I guess the actual compression is not really this high and Toyota did their homework to make sure regular is just fine.

Also found this on a real world test. I know it is a 2006 but it nice to see real results. This guy found no difference at all.

Premium vs Regular for 2005 Prius | Hybrid Cars

TED

 

From Bottom Dead Center to Top Dead Center the compression ratio is 13 to 1, but in a Prius, the intake valve does not close until 1/3 of the way up the cylinder, so the air is not compressed by 13 to 1, it just expands 13 to 1.

 

I just bought an '05 and ran 2 tanks of premium to clean out anything the old owner didn't with the premium's detergent additives. I got 42 mpg. I'm finishing the 3rd tank of gas which is regular and I'm only getting 36 mpg. This is a 16% drop in performance. The temperatures have been, since I bought it, 45, 40, 39, 34, 33, 35, 36, 31, 33, 35, 34 degrees.

Is premium better in cold temperatures and on the freeway?

 

How are you tracking your mpg? There should be no difference In mpg between premium and regular, especially in cold weather when you don't have to worry about preignition and timing retard. If your MFD is displaying 36mpg and you are not driving in the mountains or in very wet conditions then I would have your 12v battery checked out.

 

In our area, Chevron's highest octane is ethanol free, and all their other octane grade do have ethanol blended in, FWIW. That aside, "premium" gas is higher octane, better able to resist pre-ignition, only needed for high compression engines.

 

One thing the OP mentioned was visiting different gas stations. I've for years done this with all my cars, figuring that different brands probably have different/proprietary detergent blends, some of them may be better/worse at cleaning out some types of deposits, and that varying them might help keep the engine running cleaner over the long haul. Is my logic faulty? Anyone else do this? (BTW, this has nothing to do with octane, just the detergents--I always run regular).
~T