Jabberwock

We ran another long road trip last week. Drove apprx 1200 miles along Golf coast with apprx 95% interstate at 65-75mph 600 miles East and then 600 miles West on same route back. Going East I ran 1 full tank of Shell brand premium and got 26.7 mpg indicated on the LS430 tank average mpg display. Going West I ran 1 full tank of Shell regular and got 26.9 mpg indicated on the LS430 tank average mpg display. I don't think the .2 additional mpg on regular has any significance.

Based on running this test test twice in the last couple of months I have to surmise that there is no difference in gas mpg between regular and premium gas on my LS430 driving flat low elevation interstate roads at (or slightly above) posted speed limit. Apparently the LS430's computer can calibrate for efficient use of either grade of gas. Note that in case of both regular and premium there was absolutely no difference in how the engine ran - using regular or premium the LS430 idled and ran smooth as silk with plenty of power.

I have no zero agenda in terms of what gas anyone uses. Just reporting my own personal results as a data point to be of use to forum members.

qball888

Thanks for the info. In theory here should not be any mpg difference between regular and premium, they both has same amount of BTU. Premium does have more cleaning agent and additives to delay combustion which prevent premature destination that helps with getting more power out of the engine. Most modern engine can adjust/retard timing for regular very well so you should not see a huge difference in power even,

Lavrishevo

iTrader: (1)

The loss of efficiency with running 87 as the computer retards timing and equals a less then ideal detonation of the fuel in the cylinder is not a good thing. It is a safety system to prevent detonation and destroying the engine. When less fuel is fully burned this equals more carbon builds up on the top of pistons, valves, pre cat O2 sensors, cats, and other areas. Not to mention the fuel has less cleaning agents in it.

Over long periods of time running low octane fuel will cause premature failure and build up more carbon in engine which will attribute to even less efficiency and failure. One reason LS400 owners were loosing their cats early. This is my best understanding of why Lexus says premium only and not recommended. Seems to be a common theme across all high compression V8's. But with all things being equal obviously a more efficient engine is going to get better mileage.

XJSFan

If I go on a long hwy trip, I may use regular gas but around town, I always use premium... I always wondered over ten of thousands of miles, how clean the pistons, valves would be by just running regular. I would think that using premium fuel the pistons and valves will stay cleaner longer in addition to the positive crankcase ventilation valve...

lorenr

iTrader: (1)

That was probably Interstate 10. I drive a large diesel motor coach and have driven many US highways. On that stretch of road from Houston to Florida I got the best MPG I've ever gotten with the thing.

VERY flat, smooth, straight and no load on the motor. Near the coast with denser air to. I'll bet your computer's knock sensor didn't pick up a thing. Now out west here, its a different story

chris81964

I did over 200,000 miles on two different vehicles. A 2002 ML 320 original owner totaled it at 245k miles. Ran regular for more than 145k of those miles. No problems. The car was driven hard. Saw 6000 RPM very often.
Had a 2005 LS 430 I purchased in 2010 with 79,000 miles. Got rid of it last October with over 205,000 miles. Ran regular most of the time took her to 130 MPH on a few occasions. No knock, no fuss no muss. I have a friend that owned a GS 430 regular fuel only. it is a choice that people make. These cars are designed for multiple markets. The manufacturers know that fuel quality is inconsistent and have designed that into the cars.

airchomper

I think we're all equally ill-informed about why Lexus recommends premium fuel.

The compression ratio is (all things considered) not that high at 10.5:1, I've seen motors with 12.5:1 ratios specify regular gas.

And in my Honda motorcycle (which is basically my test engine since I can ride it as hard or as easy as I want) I actually get better milage and make more torque (but lower power) with low octane gas.

My thinking is that low octane gas is easier to detonate, so it takes marginally less work to bring low octane air fuel mixture to combustion. And that seems to agree with the higher perceived torque, the engine is working less to bring the mixture to the combustion event. However, when you're trying to make horsepower, you really need to control the combustion event perfectly, since gas engines make their horsepower by spinning fast, you need a mixture that won't pre-detonate: high octane gas is used for this.

Personally, I think Lexus recommends the high octane because the car gets better milage with it in the EPA test cycles. I think in the real world, you burn the same amount of regular vs premium while sitting at a stop light. And you burn the same amount of gas going down the road at a steady state.

If you need a lot of power, you'd probably burn less high octane gas, but then we have to discuss cost effectiveness.

Me? I burn 89 octane unless regular is much cheaper, or 91 octane is nearly the same price.

Jabberwock

I typically run premium around town because my local Qiktrip and Costco gas is relatively inexpensive and I fill up the tank maybe once every 3-4 weeks. Easy road trips is where I feel like I can run regular - save some money and seems zero issue with the car. The two recent trips testing tanks of premium versus regular have been on I20, I10, and US 98 and US 49...running between DFW and Mobile, Al. The range on the LS430 with that good size 22.2 gallon gas tank and 26.9 mpg is pretty amazing. One of the best long range road cars I have ever been in. Running 75mph at apprx 2300 rpm car feels like it is loafing. We do use some really nice memory foam seat cushions because the stock seats start hurting about 3-4 hours into a long drive.

ls430lover

for the post , great information,
couple of thoughts
wish i had your 6 speed auto mine had the 5 speed and got 1 or 2 mpg less per gallon

one of the reasons i got rid of my 02 was the ecu was faulting and when i would use regular it would detonate so i couldn't use more than a 75/25 split if i i did it would detonate

thus my 550$ month in gas

my camry xle getting 30 mpg combined after 8k of driving almost saving 250 month on gas

thanks for the post