Jabberwock

Just got back from 2,000 mile road trip to Florida. Wanted to test mpg on my car using premium versus regular gasoline. Gas used was Exon and pump posted as up to 10% ethanol. I ran approx 70 mph on average using lots of cruise control. Not much elevation changes and mostly low elevations along Florida Gulf Coast. Temps were apprx 48-68 degrees. I ran at least an entire tank of each octane grade on the trip. On regular (87 octane) I got 25.6 reported tank average. On premium (91 octane) I got 26.5 reported tank average. No discernible difference in engine smoothness or power but this was a very easy non challenging drive so no discernible performance difference could be expected. Gas prices averaged $2.32 for regular and $2.70 for premium. Given the apprx 16% price increase for premium with only 4-5% mpg increase over running regular grade, I would say that running regular for long Interstate road trips in the apprx conditions I ran makes good economic sense.

I was surprised that the regular ran so well with only very minor loss in MPG rate. Obviously this is a purely anecdotal test and completely non scientific. I have no agenda on what gas anyone wants to use in the LS430, just wanted to use the opportunity to be of use to the forum and provide this data point on my specific mpg using different grade gas. And as always YMMV : )

deadguy

The premium gas that I use here in SC is 93 octane. I am interested to see what results come from this grade compared to what you found. I realize comparing my car to yours would not yield accurate results.

Thank you for documenting your results.

XJSFan

Sounds great. But, does running 87 octane over 93 octane negatively effect the engine reliability over time? I would think a few tanks of 87 will not hurt anything but using it all the time may eventually cause engine issues...

aypues

"good economic sense"...have you ever?? why degrade the life of the engine to save a dollar or two at the pump. penny wise but pound foolish.

Jabberwock

"Degrading" a car engine running low octane fuel would certainly be a bad idea. Running regular gas in a high compression engine and potentially inducing pre-ignition issues under load wasn't good idea back in the 1960's and might have still been an issue in late 1980s cars that did not yet have ECMs/MAF/TB and related sensors/running gear.

Many folks still don't understand octane ratings and how they work in a modern ECM controlled gas engine. The ECM in a gasoline engine like the LS430 V8 can easily advance/retard ignition timing and related variables to run just fine on any of the normal range of octane ratings found in regular, midrange, and premium gas available in the US. There is no "degradation" but not really sure what that even means.

aypues

you're missing the point. it makes no economic sense whatsoever to use a lower grade octane regardless of whatever harm it may or may not do to the engine. I follow manufacturer service specs and don't play roulette toying with things here and there. if you're watching money that closely you shouldn't be driving a luxury car with a V8.

Jabberwock

I certainly understand your perspective - it is good to have multiple points of view on the forum.

campisi

Thanks for the data, Jabberwock.

Stu

Agreed. My car runs perfectly fine on lower octane gas on the highway. Only did it once but could not notice any difference.

In the city, there is a difference that I could feel.

1WILLY1

iTrader: (9)

lol theres always that one guy in every thread that has to go on the attack.

jrnevils

Jabberwock; Thank you for your efforts.I will certainly consider this,especially when gas prices rise to the level they were 2 years ago.

Tom57

I've been running 87 for over 240K miles ... no knock or pre-ignition issues whatsoever.

XJSFan

That's good to know. Thanks...

Lavrishevo

iTrader: (1)

In my experience, the LS can take advantage of the higher octane fuels allowing the ECM to advance the timing as much as it can. Consistently I have seen my best MPG with treated 93 octane fuel. Supper fuel I like to say.

Now I will say that certain fuel suppliers put less additives in lower octane fuel. Combined with the ethanol this will cause additional carbon build-up in the engine. I don't bother trying to find fuel without ethanol I just run a fuel good system cleaner every 5k miles or so.

Jabberwock

Agree - I try to avoid Brand X lowest cost non Tier 1 suppliers because many do not use additive packages that help clean burn and avoid carbon buildup.

http://www.toptiergas.com/retailers.html

Around DFW area I most often buy gas at Quiktrip or Costco - both are Tier 1 suppliers with good quality additive package added in all octane grades they sell. Around DFW there is one giant fuel distributor and all brands buy wholesale gas from them - each brand can pay extra for the additive package or save money by not adding the package.