Premium or Regular?

[zencat]

I've always owned performance cars (BMWs) so I've always filled up with Premium gas. I've continued the habit with my Prius...but is this necessary? I figure better gas is better for the car and I want to do everything to take care of my car, but is the difference negligible? When it comes to a hybrid, does Premium gas make any difference in performance or MPG? Thanks in advance.

[jay_man2]

Regular, Plus or Prem?

Shell regular here.

[qbee42]

It is not only unnecessary, but it will reduce your gas mileage. Premium gas is only an advantage in engines designed for premium. Why not try diesel fuel, as it has more energy per gallon? The answer to that is obvious: the Prius engine in not a diesel. While using premium gas isn't as silly as using diesel, the same concept holds true. Use the proper fuel for your car. In the case of the Prius, this is 87 octane (85 at altitude).

Tom

[blippo]

regular here

[bwilson4web]

Originally Posted by zencat

I've always owned performance cars (BMWs) so I've always filled up with Premium gas. I've continued the habit with my Prius...but is this necessary? I figure better gas is better for the car and I want to do everything to take care of my car, but is the difference negligible? When it comes to a hybrid, does Premium gas make any difference in performance or MPG? Thanks in advance.

My dealer filled the tank with Shell 89, E10 and I was able to run a hill climb test with that tank and later, a tank of Shell 87:

The Prius can 'tune' in high power settings to use 89 octane and continue up the hill on gas power. In this case, a 6% grade hill at 80 mph. But above 80 mph, the 87 octane requires the engine to 'de-tune' and make up the energy deficit from the traction battery.

If my wife is driving and we are headed to the mountains, I'll top off the tank with 91 octane to mix with the 87. But if I have enough time, I'll burn down the 87 octane and fill with 89, a mid-grade.

Now if I'm driving the mountain segments, I'll run 87 octane and keep the speed at say 70 mph. It really depends upon how many mountains and what speed you want to climb at.

Bob Wilson

[qbee42]

Originally Posted by bwilson4web

<snip>
It really depends upon how many mountains and what speed you want to climb at.

Bob Wilson

And how high the mountains. At altitude, 87 octane is more than the Prius needs.

Tom

[zencat]

Wow. Thanks. I'm glad I asked the question. I've been putting in 92 (or whatever the highest is) since I got the car. No more!

Man, this is the car that just keeps giving.

[TKY]

Originally Posted by qbee42

And how high the mountains. At altitude, 87 octane is more than the Prius needs.

Tom

Tom, In Denver, altitude 5,280 ft, give or take, 87 isn't available at any gas station I frequent. My choices are regular at 85 and premium at 91 octane rating on the pumps.

I hadn't thought about using premium when I head into the high country (across the rockies) on either I-70 or up to Wyoming and across I-80. --TK

[bwilson4web]

Originally Posted by TKY

Tom, In Denver, altitude 5,280 ft, give or take, 87 isn't available at any gas station I frequent. My choices are regular at 85 and premium at 91 octane rating on the pumps.

I hadn't thought about using premium when I head into the high country (across the rockies) on either I-70 or up to Wyoming and across I-80. --TK

You might want to consider doing some hill-climb tests like I did. What you are looking for is a plateau where the quantity of fuel needed to reach a fixed altitude levels out at higher speeds. Then use the next slower speed when running that octane when going up the mountain or hill. This will minimize drawing significant power from the traction battery and help it avoid excessive heating to hopefully last longer.

Our studies have shown that 'heat is the enemy' and the batteries get warmest from:

1. ohmic heating during discharge
2. ohmic heating during charge with exothermic reaction from charging
3. ohmic heating during discharge > endothermic discharge reaction

So we're finding a trend in the NHW11s that early traction battery losses tend to occur:

• hotter climates
• more hills (Texas hills qualify) and mountains
• higher speeds in the above areas

My hypothesis is if you can climb hills and mountains at a slow enough speed to avoid drawing traction battery power the traction battery will have time to dissipate the heat that will happen on the downgrade charging. Then using "B" on the downgrade shunts some of the excess energy out the ICE so the traction battery isn't charged as rapidly. This is at best a model based upon individual measurements and would take a substantial effort to validate. But the little data I have indicates this is likely to be the case.

Bob Wilson

[qbee42]

Originally Posted by TKY

Tom, In Denver, altitude 5,280 ft, give or take, 87 isn't available at any gas station I frequent. My choices are regular at 85 and premium at 91 octane rating on the pumps.

I hadn't thought about using premium when I head into the high country (across the rockies) on either I-70 or up to Wyoming and across I-80. --TK

85 octane is recommended at your altitude. As Bob points out, you may find situations where a higher octane may help with hill climbing, but only testing will tell. The Gen III is a new engine, and I don't have any data for it.

Tom