9000revs

18 city and 26 hwy on my 2000. Even in city, I have medium/minor stop and go commute.

AFLS400

I just drove my 98 with 185K miles from Odessa FL to Barnwell SC without stopping for gas. I was running up I75, SR 301, I295, I95 and SR278 with three other people, a trunk full of luggage with the A/C on the entire trip. With three stops along the way for bathroom and food breaks, The trip was 427 miles and I drove around a bit before I decided to get some gas. By that time I had driven 440 miles and the low fuel light never came on. It took 17.8 gallons before the fuel gun shut off. I used the same method when I filled up in Odessa with Sunoco 91 octane. The trip computer showed 26 mpg average, a tank average showed 25.8 and 66 mph average. I had the cruise set at 75 mph but the three stops and state roads (small towns speed traps) dropped the average to 66 mph. Base on the owners manual stating I have a 22 gallon tank, I should be able to easily drive 500 miles on a tank before thinking about filling up especially if it is strictly Interstate driving. I love this car !! I can't think of another luxury car, much less an 18 year old luxury V8 that can do that...wow!! By the way, the return trip to produced almost identical results running Shell V-Power 93 octane. I may try mid-grade in the future to see if I get similar results. My normal mpg is 19/21 city and 24/26 hwy, running 235/45/18s on Megan coil overs with no other engine or exhaust mods. My only issue with the car is having to change the timing belt every 90-100K. I wish it had the timing chain to save on the $$, but I shouldn't complain because this is a great car that I want to keep forever.

rayplumas

Check your actual speed and miles driven with a gps. Your phone will work. Every Lexus I have been in shows speedo at 70. Actual mph is 65-66. Recording mileage may or may not be actual miles driven. If you don't believe your GPS, a speedo shop check will confirm. :

AFLS400

Ok. The mileage from my location in Odessa FL to Barnwell SC was obtained through my phone's GPS which I followed so that's how I came up with the distance travelled. Either way, I am happy I can drive that far in comfort between fill ups.

Rdrcr

The first tank of my new-to-me '94 yielded 18MPG mixed city/highway.

But that was mostly city driving and 2 trips to the dealer and an emissions test...so lots of idling.

Mike

peace101

I manage to get 30.7mpg on my trip from New Mexico to Louisiana. 1998 with 188120. I usually use shell v-power 93. Most of the trip I was going 75mph.

dicer

And going fast is the reason for good mileage. That is the only reason a jet plane gets any kind of economy when burning some where in the range of 2 gallons a second.

sndlight

my personal best tank was 510 miles (about 26mpg). 90% highway roundtrip from IL to WI, did 65mph the whole way. I just wanted to see that trip roll to 500 and when it did I was only a few mins away from a gas station.

according to my ultragauge, blasting around town i'm lucky to get 17mpg on any size of a city trip. lets just say i love when a red light turns green.

my best fuel economy comes at 50-55mph (yes this pisses everyone around me off) - but i get 35mpg all day at those speeds. i'm not the fastest driver around but I still have fun sometimes.

during 30+ mph winds i get more like 22-24mpg on the interstate at 70.
these cars are large - cross wind resistance will kill your efficiency.

YODAONE

I see 29.5 MPG 70 MPH higway running AC with 99 LS400 using 93 octane Shell V-Power.

The knock sensors cause ECU to retard or advance ignition and, or enrich and, or, lean fuel mixture based on fuel Octane rating... (Those using lower octane fuels seem to experience increased carbon build up
in the intake and, or throttle body.)

Would like to see a highway MPG comparison using 89, 91 and 93 octane fuel (87 is too low)

The other thing diminishing mileage (comparable octane gasahol and gasoline) is alcohol content in gasoline. It's heat content is lower than gasoline with diminished mileage. Not sure if 93 octane 100% unleaded gasoline is available in U.S...which as lso makes me wonder too whether car manufacturers are providing E.P.A.mileage figures with gasoline or gasahol..

I researched information on stall speeds for Toyota/Lexus; A650E, (98-00 LS400) and A340E(90-97 LS400):

Page SS-44,Volume 1,Lexus 2000 Repair Manual RM715U1: Auto Transmission A650E,"Engine Stall Revolution, 2250 rpm".

AND;

Stall speed 2,700, + - 150rpm for the A340E (someone please verify the 2,700 figure)and 2250, + - 150 rpm for the A650E.(Perhaps how Toyota worked the low RPM torque issue on an oversquare, 4 valve/cylinder 240 cubic inch engine?)

The RPM sweeps perceptibly between 40 - 60 MPH in high gear on the 99 LS400 when slightly depressing or letting up on the accelerator during steady speed travel which suggests to me the OEM stall speed is on high side and wasting fuel

Perhaps decreasing stall speed by 250-500 RPM would alleviate this......-perhaps the transmission should be doing the work here..

Possibly decreased torque multiplication and reduced damping(?), but improved mileage and less converter slippage-reduced heat generation and longer life (?)

Found GOPNH.COM in Iowa offering torque converter balancing, upgraded friction materials(they claim more durable than Toyota), increased/ decreased stall speeds, etc. for rebuilding your original LS400 torque converter...good customer service.

Appreciate receiving comments from members here...any transmission experts out there?

Yamae

What an amazing new theory!

djamps

I normally get 17-19 on mixed driving. Yesterday I looked down after a good freeway drive and it was 15. Can't get above 16 on freeways anymore which is not normal. Hooked up a scanner and the coolant temp sensor seems fine (195 degrees), long term comps were +3% and short term 0 on both banks. All o2 sensors are working and no codes. Drives fine without any perceived power loss...anything else I should look at?

sndlight

I average 24mpg on a tank of 87 or 89. 26mpg on 91 and the same for 93. The car doesn't take advantage of 93 it seems. It just needs spark det resistance.

Not exactly a measurable difference because all of my trips are a little different so the load is different. What really makes a difference for me is 100% gas. I use it when I can and it gives me a mpg increase of 5-10% guaranteed.

CynderES

1990 Ls400, billings to washington, 1700 miles, 4.5 tanks of fuel, got about 18? mpg, i did the math in my other thread...

dicer

D = RT
If you go faster you get there quicker, LS's are very low drag cars, and even with extra drag from wind resistance that can help contribute to lower pumping losses (know why?) which increases engine efficiency.

In heavy Seattle traffic how good do you think fuel economy is? If your stopped you get 0 mpg.

YODAONE

North American database of gas stations offering 100% gasoline:

PURE-GAS.ORG