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Lexus Rx400h


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I bought my Rx400h 4 months ago from Lexus hoping to get as close to 34 mpg as possible. I have filled up approximately 16 times and average 320 miles per tank. This means my actual miles per UK gallon is 22.3. (320 miles divided by the 14.3 gallon tank). However my vehicle display is telling me I am getting 29 mpg, which clearly I am not. I am surprised the vehicle computer is incorrect. The only possible reason is that I still have quite a lot of petrol in my tank when I fill up, but I feel I am running it down to almost zero (to see how many miles I can get out of it). If I were getting 29 mpg then it would be okay, but Lexus sell on the basis of 34 being achievable and the on board computer says 29, but to only be getting 22 feels wrong. I spoke to my Lexus dealer from whom I bought the car and they said "the car is fine and working normally" and that "the on board mpg figure isn't what mpg you are getting, but what mpg you could be getting if you adjusted your driving style". Again that feels wrong. Surely an on board computer can measure how much petrol is being consumed and how many miles are being driven. Has anyone else monitored their "actual" mpg or got any thoughts/comments....?? Many thanks SPT.

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How do you know you are nearly getting to the bottom of the tank?

Easiest way to calculate your mpg - fill her up to the brim and reset your odometer - drive until you need to fill her up again. see how many gallons you need to fill her up again to the brim. note down mileage on odometer.

divide mileage by gallons and theres your best answer.

If you are still getting 22 then theres a problem somewhere - unless all your driving is short trips or all urban driving....

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How do you know you are nearly getting to the bottom of the tank?

Easiest way to calculate your mpg - fill her up to the brim and reset your odometer - drive until you need to fill her up again. see how many gallons you need to fill her up again to the brim. note down mileage on odometer.

divide mileage by gallons and theres your best answer.

If you are still getting 22 then theres a problem somewhere - unless all your driving is short trips or all urban driving....

Hi Mark. Yes that's exactly how I am calculating it. SPT

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How do you know you are nearly getting to the bottom of the tank?

Easiest way to calculate your mpg - fill her up to the brim and reset your odometer - drive until you need to fill her up again. see how many gallons you need to fill her up again to the brim. note down mileage on odometer.

divide mileage by gallons and theres your best answer.

If you are still getting 22 then theres a problem somewhere - unless all your driving is short trips or all urban driving....

Hi Mark. Yes that's exactly how I am calculating it. SPT

My RX400h slightly overstates the MPG compared with "true" method described above - however it seems to be within 5%-10% accurate. Perversely 34 mpg is achieved with city stop/start driving - whereas a blast down the motorway reduces to maybe 27 mpg - never been as low as 22 - is your right foot made of lead? ;-)

Jonathan

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Hi SPT,

My 400h is now 18 months and 18,000 miles old, a few hints, tips, observations etc.

1. The fuel consumption does improve with age (when you pass 10000 or so)

2. You can acheive 34mpg, but only with a very very gentle right foot

3. The best tactic once you have reached your cruising speed, and I can do this on anything under 40mph, is to lift off the accelerator, just long enough to get regeneration started (about 0.5 second), then gentle re-apply, keeping the power meter in the dashed section, then cruise for as long as you can just on Battery power alone.

4. You should aim to deplete the Battery, charge down hill or under braking then deplete again. Obviously this does not work all the time, and you end up with the V6 on.

5. Getting bored with all the above, and just hoofing it, is always allowed, especially for overtaking

Also remember the golden winter rule, that when it's cold the only way to heat the cabin is with the V6 (air con has an electirc pump so runs off batteries in summer), so consumption drops, people have mentioned turning the heating off and wearing coats etc, but I think this is going too far.

I concur with other observations, 37mpg round town and especially on steady running under 50mph (can acheive over 40). Down the motorway is constant V6 and at 95mph I only ever got 26-27 mpg.

Sad thing is, you do have to work at it, but it turns into a game. Also I figure that the longer you keep the V6 off, do regenerative braking etc, the long everything on the car will last??? Certainly I'd expect the electric motors to live longer than I do (given any reasonable design)

Cheers

Jon

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The way I look at it with these motors, using them normally, IE, open road driving, lots of accelerating and listening to that wonderful purr of the engine. You are going to burn fuel, not sure I have ever seen mine as low as 22mpg, but I have got it down to 25mpg, which I would expect considering how I am driving it.

Round town, I easily get 45mpg as I spend most my time on elec motors with occasional engine on tick over.

The fact is, for the 25mpg, I am getting something that accelerates at the same speed as an Audi Q7 4.2ltr but at a third of the emission output, so lower tax, better consumption... Better all round. Not only that a Q7 would be giving you about 16mpg!

My average in and out of town is about 27 - 28mpg, which I think is brilliant for the size and performance of car. I am sure if I did more town use I would get better.

My point is, if you wanted to buy this car and expect to get Ford Focus 1.6 fuel economy, you have been very mis-informed, for the size of car, it is good on fuel, in the scheme of economy and cars, it is not that great.

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If your car is 'brand new' (and therefore only 4 months old) then you need to let the car (and engine) 'run in' more before you find the car has settled. This is the case for every brand new car - so don't panic is what I'd say to you - your figures should improve with time.

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My RX400h is 15 months and 19000 miles. I used to drive one third on motorways,one third on roads and one third in cities.

Since the beginnning, my average consumption is 10.6 liter per km equivalent to 22 mpg. The computer indicates 10 % less consumption i.e. 10% more mpg.

The gap between both values could be due to the fact that the odometer is pessimistic of about 7 %, you can verify that thanks to the speed given by a gps (so when you divide the real gasoline consumption by the indicated mileage you obtain a value higher than the real one), while the inboard computer is, may be, calculating the consumption based on real gps mileage ...

As the speed limit are now in France equivalent to the british one, my piece of evidence is comparable to the other of this forum.

Thus it seems that the consumption performances given by Lexus are very optimistic and very far from the reality.

But of course, if you compare with the consumption of a X5 3.0i or other gasoline SUV, the RX400h is much better.

Regards

Jean-Pierre

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