Just measured the mileage in my 'new to me' 99 and found that I got 24 mpg in town and back and forth to work, about 20 miles round trip on the highway. Hand measured...computer said only 22... pretty happy with that mileage.

 

Tank averaged 26-28mpg on a 9hr drive to NC.. last week. Going to NC again today.

 

Filled up with 93 octane + some Lucas fuel additive. This was from the gas station till my exit. About 35 miles. Set cruise control to 2,000 rpms. The best mileage I have seen in my 400 is when I run the Lucas product.

 

Just finished a trip.. Corpus Christi to Dallas...455 miles total...
Hand calculated to be 25.3 MPG... thought we might get better...
But at least three slow downs for construction and another one for an accident...

But not complaining too much....

Fresh plugs in a 2000 LS400 with 153k showing....
Still travels well....

 

What did the computer say vs your hand calculation?

 

I'm jealous! I get 21 MPG on average in my 1998. Granted I'm having OCV issues. I'm hoping to get closer to 25 with new plugs, wires and fixed issues.

 

If you can average around 28 - 29 at 65 mph that is about the best she will get, imo. I don't stay at a high tank average really ever. Too much city driving. But if I slow down on the highway she does great. 75 mph is about a 3 - 4 mpg difference.

 

You know... I was so interested in the hand calculation that I didn't even check the computer...but I know towards the end of the trip it was showing over 26... But did not check it as I drove around town a bit and then hit the gas station.

 

city is not worth mentioning. but on long trips 24-26 is not uncommon for mine with the 4 speed auto

 

Just made a trip from Texas to Kansas and averaged 28mpg and got 565miles out of the tank.... But now im having issues with what i believe to be the fuel pump

 

symptoms?

(fuel pumps rarely go out on LS400, unless it has like 300K miles or something)

 

The pump went out of my 96 last winter at around 160k. It would die and then not start. After sitting a few hours or overnight it would fire right up. I looked it up and this seems to be a common symptom of a fuel pump going out.

If yours is truly on the way out, don't despair! With the clever pass-thru built into the back of the vehicle changing the fuel pump is actually quite easy. I'd order a good denso pump, $125 or so, and swap it out yourself.

 

Got an amazing 13.6 today. That's a 3 mpg improvement. I attribute it mostly to my AC dying. Took quite a load off the engine.

Sent from my Nexus 4 using IB AutoGroup

 

Wow, are you carrying 1000 lbs in the trunk and towing a bulldozer? When my LS was sick it got 18-16mpg. Over 100,000 miles I have averaged 20-24mpg. You should take it in to a good shop.

 

right here on Club Lexus is as good as any shop, and better than most!

he just needs to methodically trace down the issue with us!

clearing the codes and then rescanning would be a great starting point