Regular Or Hi Test Gas?

[JohnJ]

I've read a number of discussions about whether to burn Regular or Hi Test gas in the ES350..... Thought you might be interested in this week's test.....

I drove from Raleigh, NC to Milwaukee and return this week - - 1000 miles each way - - got 31.4 miles to the gallon on the way up using regular (87 Octane) gas.... Cost @ $4.00 per gallon = $127.39....

On the return trip I burned Hi Test (93 Octane) gas... Same route.... Same speed (72 in a 65; 77 in a 70 zone).... Cruise on all the way....

Got 33.7 miles to the gallon on the way back using Hi Test (93 Octane) gas..... Cost @ 4.25 per gallon - $126.11 - -

Therefore I actually saved $1.28 using Hi Test.... :P

I've been burning Hi Test all along so I guess I'll stay with it now that I've run this real life test....

JohnJ

[appleton]

Which way was the prevailing wind? :)

[nyuhsuk]

Milwaukee, WI : 600 ft

Raleigh, NC: 434 ft

That may be one of the contributing factors to the MPG difference...

[AZ08LexusES]

Milwaukee, WI : 600 ft

Raleigh, NC: 434 ft

That may be one of the contributing factors to the MPG difference...

Maybe you should do 10 of these trips with each octanage and measure by round trip. Then take the average of those trips, and compare. That should normalize atmospheric and environmental differences from trip to trip and get a better estimate as to the difference in MPG's. Or just use Hi Test and not worry about it!

[JohnJ]

Actually I was thinking that since Milwaukee is north - - it's probably all uphill (at least it looks uphill on my globe) - - then downhill to back to Raleigh.... JJ

[KBRX330]

You were being pulled on the return trip by the Earth's angular momentum and electromagnetic field and by lunar gravitational pull with some additional help from a prevailing North wind. To be accurate you should load your ES on the next shuttle trip and perform the same test in zero gravity.

[LexMusic]

You were being pulled on the return trip by the Earth's angular momentum and electromagnetic field and by lunar gravitational pull with some additional help from a prevailing North wind. To be accurate you should load your ES on the next shuttle trip and perform the same test in zero gravity.

I was not told by my salesman about the premium gas preference, so I initially used just regular gasoline.

When I started to use Plus Octane (89) I noticed a 10% jump in MPG, using the internal computer system.

I have done this test several times on the same highway of just under 400 miles and my MPG change has always been the same; +10%.

Since the 89 Octane never costs more than 10%, I have kept using it with great results in power and mileage.

[bigbill32]

for some reason on my NY to FL trips my mileage seems to be better heading south, 33+ mpg

[LexMusic]

I have also noticed a few things about gas mileage.

One, the on-board computer is not accurate. If you simply fill up and do a quick calculation, the OBC adds about 2 MPG to the equation.

[earossi]

The Lexus will run on regular grade fuel (87 octane) just fine. The engine computer may end up retarding the spark a tad to account for the lower octane, but the car will run fine. What you give up is a few horsepower. But, the ES350 has so much power that you will not miss a few horsepower.

In reality, you should actually get LESS gas mileage on premium fuel than on regular. This is because gasoline is really a mixture of a number of hydrocarbons. In order to increase the octane number from 87 to the 91 (or 93 in some areas) premium octane number, the refiners add octane inhancers such as butane to the mixture to get the increase. The problem is that the butane molecule has less energy in it than other lower octane constituents of gasoline. "So, to get the same energy release, you have to burn more molecules of butane.

If you make the trip you mentioned often, I woudl suggest changing the sequence of fuel you use. Run reular one way and premium on the return trip. Then reverse that on the next trip.

[LexPaul]

The ES 350 may 'appear' to run just fine on 87 octane in the short run and may well indeed do so for some time, but the engine certainly was not designed to run on 87 octane, and if you are unfortunate enough to experience rough idling and/or engine knocking then you will know the reason. Also persistent knocking can cause premature engine failure. I'll throw my hat in the ring with the engineers and designers. Cheap is not always better or beneficial in the long run... B)

[amf1932]

[LexPaul]

Now that is an interesting read from your 07 Owners Manual, because Lexus has actually added a few more important 'additions' after ".....you may use unleaded gasoline with an octane rating as low as 87 (Research # Number 91).....in the 09 owners manual they added after that paragraph the following: "Use of unleaded gasoline with an octane rating lower than 91 may result in engine knocking. Persistent engine knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline". I just couldn't place less than the recommended grade in my Lexus, why take the risk? I believe in adding this 'warning', the designers want to really emphasize that the engine was not designed to 'optimally run on any gas less than 91 octane and that problems may result. Sure you probably won't notice much difference, but certainly the engine is running in a degraded mode, hence possible premature wear in the long run or maybe not? ...At best its a calculated gamble. Why cheap out on a $40k + car??... B)

[amf1932]

Persistent engine knocking can lead to engine damage

Of course this statement holds true, as it has for many years, but concerning my Lexus using 87 octane fuel, I have NEVER heard knocking(pre-ignition). On all my previous ES's, '91, '94, 03, 07, I originally started using 93 octane fuel, but switched to 87 since I didn't find any performance or gas mileage differences.

Maybe you can tell me why the 6 cylinder Toyota Camry's requires regular grade fuel since the Lexus ES350 has the same basic engine....including the same compression ratio, etc. ;)

[lowrideraz]

Persistent engine knocking can lead to engine damage

Of course this statement holds true, as it has for many years, but concerning my Lexus using 87 octane fuel, I have NEVER heard knocking(pre-ignition). On all my previous ES's, '91, '94, 03, 07, I originally started using 93 octane fuel, but switched to 87 since I didn't find any performance or gas mileage differences.

Maybe you can tell me why the 6 cylinder Toyota Camry's requires regular grade fuel since the Lexus ES350 has the same basic engine....including the same compression ratio, etc. ;)

You are correct, the Camry and the ES share a compression ration of 10.8:1. However the ECU is tuned differently to ekk out a little more horsepower and torque from the ES. My wife went from a Camry V6 to an ES, and she tells me she can feel a difference in power. I haven't driven either of her cars to make a decision on that myself, but I believe what she says. Now, since we know the ECU is tuned for premium and Lexus tells us to use it. Why wouldn't we? As has been said above, this is a $40K car, why not treat it as one.

Lou

[BillyShaft]

As has been said above, this is a $40K car, why not treat it as one.

Dude...no kidding, right?

There seems to always be an endless series of posts on any auto forum that has people who want to do anything other than what the manufacturer recommends. Which oil? Synthetic or dino? Which plugs? What oil change interval? Which grade of gas?

Newsflash: there is no conspiracy! The auto maker does not want you to pay more for fuel or oil or plugs, and they don't specify sub-par components to make your junk fail early.

The same engineers who designed and built your car offer you the best educated recommendation for all of these things. Why wouldn't you trust the designer/builder recommendation more than some idiot named BillyShaft on an anonymous forum? :D

The moral of this short rant? Do what the Owner's Manual says and you will be golden.

[LexPaul]

...Well said lowrideaz and Billyshaft...This time I have to agree with the Billyshaft's on this one...