@ariescrown , that sounds pretty normal. 17 and you say you are not driving on the highway. All the amazing numbers we are quoting are highway. If you look at my post I am at 18 in town, usually drops to 17 and even 16 in winter when I am running everything in the interior, and winter tires.
But if you are concerned, and you are running 32 PSi in your tires, you could bump that up by 5 or so.
*Also, since you have the 04, leave it in "D", and don't sport-shift it, if you are doing that.

 

I partially agree here, but I have occasionally done the math just to check, and it is not dramatically off.

 

^ I agree, there may be nothing at all wrong with ariescrown's car. If I drove all in the city I would get 17 mpg too. Driving habits, your route and length of the trip, and the number of starts and stops dramatically affect mileage.

A test to see if you car truly has something wrong with it is to drive on perfectly flat ground at a steady speed above 45 mph in high gear for a few miles and watch the instantaneous mpg readout to see roughly what it is averaging. If it is in the low 20s, you have a problem. Upper 20s or above, your car is fine. I have a 2 mile long floating (level) bridge to cross routinely with the speed held at 45 and It always reads a little above 30.

 

You answered you're own question prior to asking it...
Even a healthy car, under typical circumstances, will PROBABLY not see anything over 20mpg during city driving.

 

Thanks to All you guys highly detailed and professional help on this matter. I have to say I learned a lot...

 

I feel like my 04 gets 28hwy pretty regularly, but I never calculate it out anymore. Just fill it up and try not to look at the pump and see what it cost. I just accept the 20-22mpg average.

 

In town short drives (<10km) with lots of stop and go, fuel economy is not great, 12-15L/100km (16-20mpg).

My best repeatable highway mileage on my 2002 UL (5spd) was 9.0L/100km = 26.1mpg. This requires cruise control, 2 passengers or less, very light cargo in cabin and in trunk, and doing closer to 100km/h using Shell V-Power premium grade. At higher speeds on my highway trips with a loaded trunk, I get 9.5-10.0L/100km = 23.5-24.75mpg on Costco Premium (top tier).

Been rolling on the same Michelin Primacy MXV4 225/55/17 at 35psi for the past 11 years, getting new Pilot Sport 4 tires very soon (1st of 16 tires in the 2020 ADAC 18 Inch Summer Tyre Test, 2nd of 11 tires in the 2020 AMS 18 Inch Summer Tyre Test, 3rd of 20 tires in the 2020 Auto Bild Summer Tyre Test).

Every 8000km, I put in a full jug (4.5L, 4.73L, or 5.0L) of brand name synthetic 5W-30 and use Toyota V8 filters (90915-20004, 90915-YZZD3, 90915-YZZD4). Every 1 or 2 oil changes, I put in 2 x 1L jugs of Toyota T-IV transmission fluid. Spec says 1.8L is supposed to come out but I'm measuring closer to 1.6 on a flat-ground drain until nothing more drips out. Always check dipstick when hot to make sure it's not overfilled.

Cheap and easy fuel economy improvements to do once every ~100,000km or every ~5-10 years include: new PCV valve (12204-50020) and grommet (90480-18001), engine coolant temperature sensor (89422-30030), vacuum switching valve (25860-50100), MAF sensor (22204-0D030), 24F battery, change rear differential gear oil every 32,000km with synthetic 75W-90, 80W-90, 80, or 90, and get an alignment somewhere that has a Hunter Hawkeye Elite and knows how to use it.

Bought new fuel pressure pulsation dampers (23270-50012) but haven't had time to put them in. If you have lots of free time and money, replace all 4 O2 sensors with new ones (outrageously unnecessary but you'll likely see a very small increase in fuel efficiency). Three of my 4 O2 sensors were installed at the factory 18 years ago and still running well. My front right sensor's heater element died at 7 years in-service at 80,000km, must have been a manufacturing defect.

Tried fuel system cleaner once years ago but likely a waste of money due to always using Top Tier gas, saw zero improvements in anything. Do not recommend this, these can cause more harm than good. You're better off filling up full tanks at different Top Tier gas stations (https://toptiergas.com/licensed-brands/) to clean your fuel system. The various brands have varying cleaning packages but all are good. I think Shell has the best fuel, but Costco is much cheaper, and both are Top Tier anyway.

 

Big difference in highway and city mpg due to LS430 size and weight. Short starts and stops with a big heavy car are really bad for mpg. On the highway the LS430 shines due to is super low coefficient of drag. Lexus used 400 hours of wind tunnel test time in development tuning the LS430 to be both very smooth aerodynamically and very quiet at highway speeds.

 

I've reached the high 20s on state highways where the speed limit is lower (55ish). Otherwise, I get 18-21 city and 24-26 highway.

 

In my '05 LS430, my best tank of fuel was 560 miles on 22 gallons of premium. I literally drove from Houston to Baton Rouge and back without filling up. I might have gotten even better than ~25.5 mpg if I didn't have such a lead foot.

I have only not used premium once, when I first got it. The performance difference felt very noticeable to me (could have just been confirmation bias), but my OBDII was also throwing engine knock codes (this could've just been due to bad gas but I doubted it at the time). After that, I figured premium is what is recommended, so premium is what I'll use. Outside of road trips, I average 1 tank per month (1 every 3 months during COVID), so the extra cost isn't a big deal. Also, I've been averaging 50 cents off per gallon from our grocery store [Kroger], so we're milking that for all it's worth too.

 

I have made it a point to use 93 octane gas in my 2006 LS430. The oxygen sensors tend to act up if i use lower octane. At 556,500 miles I try not rock the boat. Mileage holds at 23.5 to 24.2 . I normally drive between 55 and 80 mph. Around town only my mileage would be about 18.
I am an original owner.

 

@Wsysynjr an 06 with 556k!?

WOW, thats awesome! Stock trans?

 

2003 with 282k here. Computer avg readout pretty much stays around between 23.5-25. I always use cruise and 93 at the pump. A/C doesn't seem to make a difference.

 

Yes original engine and 6 speed automatic with original trans fluid. Deal refused to change. It is a sealed system. Now too many miles to mess with.

 

Premuim only, 30+ at 65 all day.