Poor Fuel Consumption

[Keith Bowler]

Have has my LS now for a couple of years and until this week had not really taken it out on a good run.

Went up to Leicester in the week from Kent and was rather dissapointed by the fuel consumption of just around 25mpg average on the motorway section of the journey when I at least expected low 30's.

I had suspected the computer to be faulty as I only get around 16mpg in normal short trips.

I am not a speed merchant so kept speed to within the legal limit. There were some roadworks and holdups which would have caused a slight reduction in mpg but nothing extraordinary.

I am not mechanical expert but my mpg return does not seem right.

Car is regularly serviced and repaired when needed regardless of cost and runs faultlessly with no visible signs of any faults and there is no evidence in the service history of any repairs that would indicate a previous engine problem. Emmissions test at last MOT was fine and way within limits.

What do you chaps reckon might be wrong, I suppose my first check should be lambda sensors and the CATs which I have been told may need replacing soon.

[Ruud]

Did you go by the trip computer or actually worked it out?

[Malc]

I doubt there is actually anything wrong with your fuel consumption with your car. Averaging 25mph on a longish stop start run in any 4 ltr limo is good !

The best I ever managed was just about 30mpg ( on each of my Mk1, 2 and now Mk3 ) when running at 80mph on cruise and fully loaded. I found the car actually performs better fuelwise when it is fully occupied with passengers and loaded up.

Foot lightness control with the accelerator is also a major influence too .

I may be wrong of course, but have used my Ls400s as daily transport for 12+ years now and think 25mpg ain't at all bad

Malc

[Cotswold Pete]

Mk4 - I get 24 to 27 on my morning commute - which is a 200metre climb at the start and then flat for 10 miles. On the motorway, fully loaded with aircon on, 80-83 mph, I get 31mpg on long motorway run, and it 50-60 mph, get as much as 35mpg.

This is based on trip computer.

Did a long run to Scotland two years ago and did it by topping up and then topping up on re-fill and it confirmed the numbers I get from trip computer.

I have never got less than 20mpg on this one and previous Mk2, and it is mainly rural driving.

I do find 50mph on rural roads give me worse mpg then 50mph on motorways, assume that the slowing down and speeding up on rural roads is enough to eat a bit more juice.

[Gbneil]

Mine seems to average 23-27mpg mixed driving and best was long haul to hull and back, spookily 666 miles door to door, air con on, cruise on at just under 2k revs....about 58mph?....34 mpg....delighted with the fuel...I only bought my ls for the summer when I work a lot and cover a lot of miles and plan on selling it August September time when I go back to university....but parting wil be such sweet sorrow....and the mpg figures above make 'man maths' justification easy....I expected 20 mpg or there about...

[cruisermark]

i do mostly town driving in my LSs

when i had my mark 4 the best i got over 120 mile trip was 29

my 430 shows 20 most of the time as most of my driving is local

[gkkes]

Read it and weep chaps!

On the Paris to Aberdeen leg of my current business trip.

This picture was taken just north of Ecclefechan in Dumfries and Galloway. I'd slowed a bit for my passenger to take the snap.

Even discounting the channel crossing it's mighty impressive. I would also possibly discount 10% as I have smaller wheels on mine! my Iphone SatNav shows this discrepancy in actual and indicated speeds

[Bluesman]

I can get mine to read 99.9 miles to the gallon @ 70mph but we are going down hill with no throttle being applied. On LPG as well Mike

[The-Acre]

I can get mine to do anything from 15-99mpg all within 10 seconds, because like various other things on what I thought was a good car it doesn't work properly! I wonder how my old 400 is doing with its new owner......everything it should do I suspect.

[Keith Bowler]

Perhaps I won't get too worried then

I measured mine both by brimming tank and checking what it would take to refill and the mileage travelled which checked out with the trip computer.

I use my aircon all the time and cruise control when I can so I expect that would count for a few less mpg.

Thanks chaps

[AndyCheltenham1]

I have had my LS400 for over 6 years now and it runs perfectly, has passed every MOT on emmissions and as far as I can tell there is nothing at all wrong with the engine or the way it performs-yet I manage around 18mpg on average. I do mainly local runs with occasional longer runs.The best I have ever had on a long run (ONCE ) was 29mpg, and that was driving at a steady 65mph. After constantly reading what other owners are getting mpg wise I have spoken to my mechanic a few times and he assures me that my mpg is about right for a 4 litre V8.

On searching online for more official mpg figures ( as opposed to owners club members figures) my mpg seems more in line with what you should be getting. If you search on many American sites the official figues go from-19/25, 16/22, 18/23 (city and highway).

The one site I went onto which is www.fueleconomy.gov (the official US government source for fuel economy information) gives the mpg as 17 (city), 23(highway) and 19 combined and as this is an official government site I would assume is fairly accurate??

I know if you look at any published mpg figures here in the UK they are nowhere near what you will actually get, yet if you look on an American site the exact same car will get significantly less mpg over there!!

I don't want to offend anybody on here but I find it hard to understand how these mpg figures are obtained when they are often much higher than official sites and even Lexus themselves would claim??

[Titch LS]

Keith, it depends what speed you call 'motorway speeds'. I have had 30 mpg on the motorway by not going more than 65-70. One thing I found out from another site is that replacing your old coolant temperature sensor can increase your mpg. I don't think it is too hard to DIY and not too expensive either. Might be worth a try if you're really bothered. Otherwise I would say that 25 isn't too bad for 80 mph plus.

[graham8370]

Andy,

''I know if you look at any published mpg figures here in the UK they are nowhere near what you will actually get, yet if you look on an American site the exact same car will get significantly less mpg over there!!''

The US gallon is much less than the UK imperial gallon

[jpjsavage]

When I was running my Mark 4 LS400 I routinely got low 20s on fuel but definitely mid 20s on a run up the M6. The LPG installation done by the previous owner was very good though. I'd get around 225 miles at least out of £30-35 of LPG.

[Gbneil]

We don't buy these cars for fuel economy. Iv owned many big engined barges and found them all to be much of a muchness....some as low as 17-18mpg round town but most over 30 mpg on long runs....the ls belies it's barn door looks with a cd of .29 as far as I know and this makes it one of the more acceptable long haul cruisers...town driving kills big engined cars....the lowest I have had behaving round town is still 19-21 mpg but as I said 23-27 seems to be my average depending on the ratio town to open road....this is a heavy car with a 4 litre v8 and almost what, 280hp?....pretty good, I expected much less to be fair....

Worst I owed was a '72 volvo 164 3 litre on carbs....it seemed to return 14-16mpg regardless!...my old jag xj /series 3 4.2 rarely saw the SUNY side of 20 mpg either, but it was, in my opinion, the most beautiful salon car of all time so i forgave it daily...

[goldtop]

Andy,

''I know if you look at any published mpg figures here in the UK they are nowhere near what you will actually get, yet if you look on an American site the exact same car will get significantly less mpg over there!!''

The US gallon is much less than the UK imperial gallon

What he said. I had a Nissan Maxima QX a few years ago, and the computer in that was never correct (I always did brim-to-brim fills and knew exactly what mpg I was getting).

I suspect the Nissan's computer was calculating US gallons instead of imperial gallons, and from memory I think the latter is 20 percent more.

Also, I presume the ECU plays a big role in economy and perhaps if an LS400 has the flakey capacitor problem, it may not run as efficiently as it should?

[brendangeorge]

25 on the motor way is not bad - my wife can achive 30 by driving at 70 - I only dream of that. I can get to 25 by being a saint.

The fuel computer avaerages 22 over the life time (225K miles) - it is horrible round town.

I run on LPG and on LPG get about 18MPG for 40% of the cost of petrol. So if the petrol bill is annoying LPG is the way to go - there are many LPG disciples on the forum - I have done 125K on LPG.

Bren

[Mybikes a cx500]

My LS400 Mk4 on LPG returns 21 (calculated) long term.That's with a fair bit of motorway and dual carriageway driving.

I can get an indicated 30 if I fill up at a motorway service station and cruise sensibly, but the indicated MPG is what I would be getting from petrol, not what I actually get on LPG

[plastic orange]

I've just done about 650 miles on a trip to Scarborough and back. This is a mixture of motorway and A roads with plenty hills and stop start. I was pleased to average 30.9 mpg - and I wasn't hanging about.

I've always been impressed with the fuel consumption - worst was my Austin Westminster - 12mpg in the town.

Pete

[Malc]

Blimey, I had an Austin Westminster 3ltr for a few months back in the early 80's ..... it died on the M4 loaded up with the family going on holiday to Wales, got RAC trailered home and set off again in our Vauxhall 2300 VX estate

Malc

sorry , reminiscing . comes with old age I'm afraid

[Anthony B]

Speaking as a newcomer to this club and to my LS430: I've done about 700 miles in it so far, a mixture of short rural stop-and-starts and a few longer runs at 65 or thereabouts. I'm learning how my driving can radically change the mpg I get. Anticipation, minimum use of accelerator and brakes, cruise control wherever possible and trying to keep the revs below 1500 much of the time. I believe I can achieve 28 average and better than 32 on long stretches. If I achieve 28 this will be two thirds of the 44 average I used to get from my Rover 75 diesel, and I'll be pleased with that. The car is superb and one to keep and look after.

Incidentally it's inevitable that the instantaneous consumption figure will vary very quickly between near zero and 99.9 - watch how it changes with the revs - but that's of no relevance to cost of ownership long-term.

[Graham Gardner]

Andy,

''I know if you look at any published mpg figures here in the UK they are nowhere near what you will actually get, yet if you look on an American site the exact same car will get significantly less mpg over there!!''

The US gallon is much less than the UK imperial gallon

That's true that is

[Anthony B]

Latest update on my LS430 - I'm getting around 27 on a mixture of rural and mid-distance stuff. Longer runs I already know will show better than 30. So I'm content - the car is too enjoyable for fuel costs to be a big consideration amidst other domestic expenditure - but I'm seriously thinking about an LPG conversion next year.

[alien1974]

mine averages about 17.5 mpg according to the computer thats all round town, it doesnt matter how i drive it hard or like a nun, also the instantaneous consumption is the same, full throttle or gentle throttle inputs give the same low readings on acceleration. I have taken it into lexus and they said there are no codes on the ecu.

[Spacewagon52]

I would take it on a motorway run at around 70mph and see what you get. Town driving drinks fuel.