Miles per Gallon Issues Lexus RX 400 h

Josswallace · January 17, 2017

I have recently bought a 2007 RX 4ooh with £45k miles on the clock. Having driven fro the UK to The Tirol in Austria at speeds between 70mph and 100mph I find I am getting around 24mpg.

This is nowhere near the advertised 37mpg and I have no idea what could be causing it. Could the main Battery be not performing properly.

Any advice/guidance would be very much appreciated.

Ian Wallace

NemesisUK · January 17, 2017

Welcome to "real world economy"...

The cold weather and high speed will knock the mpg down.

chesterman · January 17, 2017

Hi & welcome. IMO 37 mpg would only be achieved under ideal conditions & driving style, ie low speed, stop/start traffic where the electric motors are doing a proportion of the work. At constant motorway speeds & up to "100mph", a 2.2 tonne SUV with a 3.3 L engine will use a lot more fuel. Add cold conditions and watch the fuel needle sinking. If the car is otherwise running well, (plenty of power & smooth delivery,) I would expect around the 24 mpg you quote under such conditions and 30+ in normal driving. Hope this reassures.

julian1969 · January 17, 2017

Has my rx400 for a week or so now and just done my first 'normal' commute Bedfordshire to Rickmansworth and back. Most of the journey was m1 / m25 with stop start traffic and cruising up to 70 with a few bursts of 'warp speed' to overtake. Got 34 mpg on the way there and 33 for the round trip. This is according to the meter on the dash not calculated fill.

This is about what I was expecting given temperature and driving type.

I'm coming from a Nissan Leaf so maximising regen by coasting and maintaining speed with a light throttle is something I'm used to. There is something very satisfying about cruising along at 60+ mph with just the yellow arrows showing.

im hoping that as the weather warms up I can improve on these figures.

ISJason · January 18, 2017

With the cold and the speed I'm surprised it's not a lot lower .. I'm currently varying between 27 and 29 mpg at the moment

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GSLV6 · January 18, 2017

The clue to 24mpg is the climate you were driving through plus the speed you were driving at and the elevation of the locatons above sea level. Official figures aren't based on 70-100mph (!). They're based on a set of standard tests and extra-urban usually optimised for 56mph constant cruising in top gear on the level in ideal circumstances. Combined is just an average of stop-start town and extra urban.

When you think about it, 24mpg is actually not bad at all for a 2.2 tonne lump travelling at an average of, what 85mph, in a cold climate on presumably some elevated locations, possible well above sea level where you'd expect a fall in power and increase in fuel consumption on the hills.

My 450h only averages 34 to 35mpg with mixed driving since I picked it up against official figures of 44.4 mpg.

rayaans · January 18, 2017

19 hours ago, Josswallace said:

I have recently bought a 2007 RX 4ooh with £45k miles on the clock. Having driven fro the UK to The Tirol in Austria at speeds between 70mph and 100mph I find I am getting around 24mpg.

This is nowhere near the advertised 37mpg and I have no idea what could be causing it. Could the main battery be not performing properly.

Any advice/guidance would be very much appreciated.

Ian Wallace

Sounds normal. My RX300 was only doing about 16mpg most of the time apart from on a run against an advertised 23mpg.

Ive had most luck in my son's 10 year old Polo. Advertised mpg is 44 and it gets 40mpg in my hands.

Josswallace · January 18, 2017

Many thanks for the replies its very reassuring for a first time hybrid owner.

rayaans · January 19, 2017

On 1/18/2017 at 5:57 PM, Josswallace said:

Many thanks for the replies its very reassuring for a first time hybrid owner.

Might be the speed as well - they seem to do very good economy at 70mph but it plummets when going over!

GSLV6 · January 20, 2017

Local 6 mile trip this morning in sub zero temperatures saw 18mpg (one long hill climb, one hill descent included)

julian1969 · January 20, 2017

I found that the MPG was dropping visibly as I was clearing my windscreen with the heater on full blast a few mornings back. Clearing the ice from the outside is not the issue it's the fogging inside that takes the time - a way to reduce this would effectively increase MPG on cold morning starts I feel - any tips?

I'm not keen on just wiping the fog away as it 1) leaves streaks which cause vision issue in bright sun and 2) doesn't prevent the fogging returning quickly enough to cause issues driving.

steve2006 · January 20, 2017

26 minutes ago, julian1969 said:

I found that the MPG was dropping visibly as I was clearing my windscreen with the heater on full blast a few mornings back. Clearing the ice from the outside is not the issue it's the fogging inside that takes the time - a way to reduce this would effectively increase MPG on cold morning starts I feel - any tips?

I'm not keen on just wiping the fog away as it 1) leaves streaks which cause vision issue in bright sun and 2) doesn't prevent the fogging returning quickly enough to cause issues driving.

Leaving the AC turned on helps as it dehumidifies the air and also make sure the pollen filter is serviceable.

julian1969 · January 20, 2017

I'll have a look at the pollen filter but I tend to leave the AC on all the time - anecdotally I've heard that this helps prevent the seals from perishing - no idea if this is true but the last car I didn't do this on did spring a leak so may be.

DanD · January 25, 2017

When I had my 400h, I drove to Munich and back in the winter and achieved an average of... 24MPG.

GSLV6 · January 26, 2017

I think that some folk expect too much of a large 2.2 tonne SUV on mixed trips in cold climates. Even the large diesel ones don't do more than mid 30's at best to the gallon (despite manufacturer's claims) and you can't really compare with a car weighing in at 3/4 tonne less with less rolling resistance which, given the same engine and drive train will always have a 10mpg or more advantage. To compare with some past cars that I've owned, in equivalent driving conditions, my 325 BMW 6-pot petrol managed between 24 and 28 mpg average, my Volvo S60t 5 pot turbo petrol managed 22mpg (28 on a run if I was lucky), my S60D5 would do 45mpg on a run and high 30's or low 40's mixed, but the XC90 using the same engine was a good 10mpg down on this due to mass and frontal area. It's just physics.

The plug in Mitsubishi mpg figures are false because they do not account for the fuel burnt at the power stations that charges them, and run purely on their under-powered 2 lite engines wouldn't fare very well at all given their 2 tonne mass.

Achieving high 20's in a petrol engined 2 plus tonne SUV isn't bad going and when the weather warms up, that figure should be into the 30's.

RobinGBrown · January 26, 2017

I know it's only anecdotal but my RX300 manages 27 mpg in a trip across Europe during the summer - I haven't tried either the 300 or the 400 hybrid in winter though. I'd definitely be dissapointed with 24mpg.

Assa1974 · January 27, 2017

On my two 200 mile commutes this week, including cold mornings, I managed and indicated 34mpg. I estimate that cruising along at 65mph gives me about 4mpg extra compared to the 70-75mph that I used to consider 'normal' motorway speed. The revelation is that it barely costs me any time mainly due to driving in rush-hour traffic so my average speed is not effected much.

DanD · January 27, 2017

On ‎26‎/‎01‎/‎2017 at 2:08 PM, RobinGBrown said:

I know it's only anecdotal but my RX300 manages 27 mpg in a trip across Europe during the summer - I haven't tried either the 300 or the 400 hybrid in winter though. I'd definitely be dissapointed with 24mpg.

What kind of speed were you driving at though? - I think 27mpg is pretty good. My average with the 400h was between 28 and 29mpg, although I have always put enjoyment ahead of economy.

People put a lot of emphasis on MPG, but in real terms, to the average driver who covers 12k miles per year (is that the average these days?) does a difference of 3 or 5 miles per gallon really make a huge difference cost wise, especially if it means compromising your enjoyment of a car?

RobinGBrown · January 27, 2017

53 minutes ago, DanD said:

What kind of speed were you driving at though? - I think 27mpg is pretty good. My average with the 400h was between 28 and 29mpg, although I have always put enjoyment ahead of economy.

Sorry forgot to say, that's at autobahn speeds - 80mph

I've recently got a 400h so I'll see how that does on the same journey, if it's not significantly better I'm going to be quite disappointed with the claimed mpg Lexus gives

sorcerer · January 27, 2017

I can't remember if it was Top Gear or Fifth Gear or maybe even something else, but one of the motoring programmes did a piece about manufacturer's claimed MPG figures and basically it's all but impossible to reach them. They are legally allowed to pull such stunts as only allowing one person in the car whilst under test and - this is the killer - even stripping out seats, carpets, spare wheel and even gloveboxes to make the car lighter and so increase its MPG on test. It's scandalous really and I don't know how it's legally allowed, but the truth is that it is.

GSLV6 · January 28, 2017

You'll realistically achieve about 70% at best of claimed figures, with careful driving. You cannot expect great fuel economy from ANY 2.2 tonne vehicle driving at 80mph and it is unrealistic to expect manufacturer's xtra-urban figures trying to push such a large brick through the air at 80mph. If you achieve high 20's for the 450h or even the 400h, you'll be doing well enough at 80. Slow down a bit to 70 or under and it makes a big difference. You'll then return mid 30's to the gallon, but as soon as you exceed 70, forget it.

Just look at the equation for drag and you'll see why.

Drag is directly proportional to the square of the velocity of an object. For those interested, the equation is:

Df = Cd (coeff) x density x velocity (squared)/2 multiplied by frontal area. This doesn't take account of extra drag from boundary separation points or vortices.

The EU standard for stating economy is at a fixed 56mph or thereabouts as this is reasoned to be where most vehicles operate at peak torque in top gear. You can see that exceeding this by even 10mph and you're asking the engine to overcome much increased drag forces. At 80mph, you're drinking fuel to overcome a substantial increase in drag,so perhaps should consider a different car if economy is a prime concern. My 3GS300 was way more economical even at 90mph Autobhan speeds than my RX is at 70. Frontal area matters, irrespective of drag coefficient stated.

RobinGBrown · January 28, 2017

I've been using autotrader to compare MPG figures

RX300 - 16mpg urban, 27mpg extra urban - that matches up with the real world figures I get in my RX300

RX400 - 31mpg urban, 37mpg extra urban - so far I'm averaging 24mpg urban and haven't done any motorway - significantly under the mpg figures from the same source

So either the figures autotrader uses are form different sources or the RX400h figures are substantially overinflated - it should be better than the RX300 or what's the point

and there's so many different opinions it's impossible to gauge anything

Grrrrrrr

julian1969 · January 28, 2017

It's going to depend on driving style, traffic density, traffic light timing, even weather conditions. So replicating manufacturers figures is next to impossible as they run on a rolling road under carefully controlled conditions

i always regard manufacturers figures as only useful when comparing vehicles on paper. A 400h is going to beat a cayenne turbo s on mpg but not a diesel Kia ceed. But then if I wanted the unreliability of the Porsche or the space to mpg tradeoff of the Kia I'd have one of those instead.