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Old 06-04-14, 01:35 AM   #1
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Default My fuel consumption - normal?

my 90 ls400 has below fuel consumption, normal or not? how about you?

City: 12 mpg (20 liters per 100km)
Highway: 17 mpg (14 liters per 100km)

Note: city average speed = 20km/h and "highway" (its what they call) = 50km/h
the consumption numbers base on my light foot driving style consistently in 8 years.
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Old 06-04-14, 06:45 AM   #2
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I am presuming that your calculations are based on U.S. gallons. Approx. 3.78 litres to the U.S. gallon.
Imperial gallons are approx. 4.54 litres to the gallon.

12 mpg probably isn't too bad considering your average speed. If you are in stop/go traffic and stopped at times you will see poor economy. If you're on the move all of the time on the "highway" then 17 mpg is a bit low imo.

I haven't undertaken an economy test.
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Old 06-04-14, 07:59 AM   #3
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My recent fill ups have been:
April 434 miles at 23.09 MPG
and
June 411 miles at 22.01 MPG...
Both are a mix of city/highway...
While my 99 will get MPG than yours... yours seems unusually low... especially at highway miles...
So we can't compare to mine...

Specs on the car when new were: (according to edmunds)
16 in the city and 22 on the highway... you're running about 75% less than those numbers...
Does not seem quite right.

Combined driving is 17 mpg...pretty close to what you're getting.
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Old 06-04-14, 08:12 AM   #4
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i get around 18/mpg with city driving on my 1994 LS400. i changed my fuel filter, air filter, pcv valve, full synthetic oil change....
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Old 06-04-14, 11:51 AM   #5
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that seems about right with how slow the traffic is. these cars get the best mileage on the highway at speeds over 100km/h. city driving it's horrible!
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Old 06-04-14, 01:46 PM   #6
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I average about ~16L/100km in my 96 with mostly city driving under 60km/h. In really heavy traffic weeks, I have seen it jump to 19L/100km.
At the same time I routinely get 10-11L/100km on the mountainous highways around here, and would probably get <10 on flat highways of the Midwest where you can sit at a speed and rpm for massive distances!
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Old 06-04-14, 03:55 PM   #7
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Quote:
Originally Posted by qha_vn View Post
my 90 ls400 has below fuel consumption, normal or not? how about you?

City: 12 mpg (20 liters per 100km)
Highway: 17 mpg (14 liters per 100km)

Note: city average speed = 20km/h and "highway" (its what they call) = 50km/h
the consumption numbers base on my light foot driving style consistently in 8 years.
That's way too low. On my 1990 LS400 I get 17mpg in city, and around 24mpg on highway. I always gas up at the same gas station and using the exact same pump. That way I have reliable numbers and I always write them down on the receipt to be able to track how my MPG changes as I work on the car.

Things to check:

- Vacuum lines, especially the ones going from the P/S vacuum valve at the bottom of the P/S pump to the intake. In my case, the little plastic part where the vacuum hose plugs in was cracked, and that ruined my MPG on a cold day. I fixed it by buying new vacuum hose in a dealership (only a couple of bucks), and repairing that part of the intake where the vacuum hose plugs in. Even if those two lines look perfect, they have probably been soaked in PS fluid for many years, and at the very bottom, they may be leaking a bit. Best to change them; not terribly hard, I did it myself.

- New wires and spark plugs. I bought NGK (3764) BKR6EIX-11 Iridium IX spark plugs on amazon.com and they are absolutely fantastic, I dare say, they are part of the reason for my terrific MPG. I also changed wires at the same time: NGK (6403) TE132 Spark Plug Wire Set. Also available on Amazon and the price there was the best at the time. They are OEM, so they are properly numbered, proper length, they make changing wires job a breeze.

- New rotor and distributor. Didn't have the time to wait for OEM, so I replaced them with Bosch, which works just fine (and is cheaper). Also from Amazon.com

- Coolant temperature sensor, the one that sits on passenger side of the engine, closer to the front. Its been mentioned many times around here and costs peanuts.

- Run something like Chevron Techron injector cleaner (on special at Costco very often), a few times

- Very important, at least in my case, was to flush the cooling system, using Prestone cooling system super cleaner which can be left in the system for few days. I did just that, and my car was running 100 times better! Before that, it never overheated, never had any visible problems, but my transmission was not running at optimal temperature due to cooling system not giving me the best performance. Once I flushed it, it was like a new car.

- I replaced all my o2 sensors with Denso (OEM), and at first I did not notice any difference, but a few days later, it all seemed to have come together and all at once there was a lot more pep to my car (this was done around the same time when I did the cooling system flush and thermostat).

- And obvious things: use only premium gas, use ONLY OEM air filter and remember to clean it every month or two, change oil regularly using synthetic Mobile 1 and OEM filter, make sure your ECU capacitors have been changed...

Basically I now only have to touch the gas pedal it is that amazing; the only time I step on it a little harder is on a very steep uphill when I am passing someone, or when merging and have to get from 20mph to 65mph in an instant.
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Old 06-04-14, 04:35 PM   #8
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Nice post PeterLS... verify informative.
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Old 06-04-14, 09:00 PM   #9
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9.5 L/100 everytime driving Michigan to Ontario, avg 115 kph.
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Old 06-04-14, 11:48 PM   #10
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You guys are neglecting the speeds he is travelling at. Drive a tank of gas at like 15mph in the city and 35mph on the highway and pot back on how good your mileage is.

I'm guessing/remembering qha_vn is in Vietnam and traffic is insane in SE Asia. Imagine driving an Manhatten/LA rush-hour almost 24-7 day, everywhere. It was when insane I was there in 05, the roads were utterly clogged from atleast 6am to 9pm in the smaller cities. Big cities like Bangkok, Chang Mai and Vientien were much worse!



It would be nice to hear back from qha about exactly what sort of traffic he is driving in because there could be absolutely nothing wrong or like Peter listed, there could be tons of things...
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Old 06-05-14, 01:22 AM   #11
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BTW, the city traffic I drive in is among the worst in N. America. Think Manhattan... Heck even my highway is stop and go quite often...
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Old 06-05-14, 01:40 AM   #12
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Quote:
Originally Posted by Shmee View Post
You guys are neglecting the speeds he is travelling at. Drive a tank of gas at like 15mph in the city and 35mph on the highway and pot back on how good your mileage is.

I'm guessing/remembering qha_vn is in Vietnam and traffic is insane in SE Asia. Imagine driving an Manhatten/LA rush-hour almost 24-7 day, everywhere. It was when insane I was there in 05, the roads were utterly clogged from atleast 6am to 9pm in the smaller cities. Big cities like Bangkok, Chang Mai and Vientien were much worse!

It would be nice to hear back from qha about exactly what sort of traffic he is driving in because there could be absolutely nothing wrong or like Peter listed, there could be tons of things...
You got me right Shmee , thanks a lot for it.

I believe that traffic in "city" and "highway" different from country to country. I stated very clear in my post that my average speed in Ho Chi Minh city (Vietnam) is 20 km/h or even a lot less (with a lot of stop and go). And about "highway", it is ashame that our highway max allowable speed is 80km/h and a lot 40, 50, 60 km/h limits a long the way. that brings average speed down to 50 km/h on "highway".

with that said, can you please provide your consumption with average speed so I will know if mine is fine. thanks all.
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Old 06-05-14, 01:57 AM   #13
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Quote:
Originally Posted by peterls View Post
That's way too low. On my 1990 LS400 I get 17mpg in city, and around 24mpg on highway. I always gas up at the same gas station and using the exact same pump. That way I have reliable numbers and I always write them down on the receipt to be able to track how my MPG changes as I work on the car.
Thank you very much for your advices, I have covered most of them.

- Vacuum lines: I deleted that line with new P/S pump that has no such valve.

- New wires and spark plugs: done. it was among the first things after i bought the car

- New rotor and distributor: done. Bosch off Amazon

- Coolant temperature sensor: done, few months back, notice no difference in fuel consumption, but pedal response is yes.

- Run something like Chevron Techron injector cleaner: done few years back

- Very important, at least in my case, was to flush the cooling system: not sure if this would have an impact to fuel consumption, but I did several time with preston coolant.

- I replaced all my o2 sensors with Denso (OEM): replaced 1 as it turned on check engine light

- And obvious things: use only premium gas, use ONLY OEM air filter and remember to clean it every month or two, change oil regularly using synthetic Mobile 1 and OEM filter, make sure your ECU capacitors have been changed...: I use K&N, gas: ron 95, Castrol 10-40, ECU caps are replaced
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Old 06-05-14, 01:59 AM   #14
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Quote:
Originally Posted by Greg5OH View Post
9.5 L/100 everytime driving Michigan to Ontario, avg 115 kph.
you are speeding at times huh . I guess it is 2000 LS
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Old 06-05-14, 02:08 AM   #15
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Quote:
Originally Posted by kevvo View Post
I am presuming that your calculations are based on U.S. gallons. Approx. 3.78 litres to the U.S. gallon.
Imperial gallons are approx. 4.54 litres to the gallon.
I use US gal. 1 liter = 0.264172052 US gallons
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Old 06-05-14, 02:08 AM
 
 
 
 
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