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Used Lexus Rx400h - Is There A Problem Here?


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I have just bought an RX400h with 30k miles on the clock. I have done about 300 miles in it myself now and never seem to get over 27mpg average, including a lot of motorway driving. The petrol engine kicks in immediately from standstill, even when accelerating very gently. I was under the impression it would only kick in at 25-30mph. Is there a problemwith my RX? What are othersexperiences of this?

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I'm sorry but you can't think of a hybrid like a diesel. On the motorway, it's simply a large, heavy 4x4 that's running on a 3.5L V6. How economical do you expect that to be?

It's only around town that you will receive the most advantage, and depending on the level of charge available is how much the car will run on batteries alone.

It also depends on how hard you press the accelerator, try pulling away gently and it will stay on electric. However, if it's not staying on electric at all, then perhaps there's a problem somewhere so I'd get it checked out :)

Welcome to the LOC btw!

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I think the OP is experiencing issues with his 400h that I have been trying to discuss on another thread.

FWIW I don't think there is any issue with your car, just that you have really adapt your driving style when using your 400h to achieve the kind of results you want. You see on a motorway, at say 70MPH+ the car will exclusively be running on the 3.3L V6 petrol engine and will return consumption commensurate with such an engine type.

On the issue of Battery driving, you will very quickly learn that if you manage to run your car on the hybrid Battery then even a slightest incline or dab on the accelerator will engage the petrol engine - so to ensure you return to Battery running only, you will need to 'lift off' the accelerator and then ever so gently apply pressure to it once the Battery has engaged to keep momentum going and preventing the petrol engine from kicking in.

You see the 400h does not switch back to Battery - even at 35MPH speeds - unless your speed reduces (by lifting off the accelerator) and then it will run on Battery power. But the trick here is to balance continuity of momentum and keeping the petrol engine off. It is a knack but I would;t suggest there is anything wrong with your car at this time.

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Thanks for your comments guys. I've been playing around with acceleration and am getting more Battery use now. Managed to get the mpg to 27.9, but it's gone down again since I came to work this morning on the motorway!

I'd have thought that motorway driving would have increased the mpg, as the manufacturer's quoted figures are higher for motorway than urban cycle.

Love the forums, by the way!

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Try switching off the Air conditioning. I find that if you do this, it's far easier to keep the car running on batteries only, for example while in stop/start traffic, or in a retail car park.

In the end though, I just leave the A/C on and don't worry about it.

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I think there may be some misunderstanding about the basic science of the 400h.

All the energy used in driving a hybrid is ultimately derived from running the petrol engine; that applies even when running on batteries only. The advantage of the hybrid set-up is that energy that in a conventional car would be lost (e.g. from over-running, coasting or regenerative braking) is "saved" for re-use; thereby making for a more efficient system. The energy management control in the 400h appears to be set up to store and reuse as much of this energy as possible, so that energy is being added to and taken out of the batteries for optimal efficiency. That's why under normal driving at say 40-50 on an A road, the energy monitor screen seems to show energy going in and out of the batteries in sometimes very short bursts. It also explains why you will very rarely see all bars on the Battery capacity meter lit up, since that would imply that there is no more capacity for energy storage. Instead the energy management control constantly monitors the batteries and releases stored energy (by running the electric motor(s) simultaneously with the petrol motor if necessary) thereby to keep spare capacity for storage available at nearly all times. The drive train of the 400h is set up to utilise energy from the petrol and electric motors simultaneously when required, so that the work done by the petrol motor is augmented by the elecric motor in many situations.

From this it follows that there is no particular advantage (apart from the Tesco car park fun) in trying to keep your 400h running on electric motor only. The energy used at that stage will have to be paid for at some later stage by running the petrol engine to replenish the batteries. (Don't forget that recharging the batteries by coasting down a long hill is paid for in getting the car to the top of the hill in the first place.)

The name of the game in hybrid technology is energy efficiency, and I think the 400h makes a pretty good stab at it. In relative terms, these are still early days and no-doubt there will be significant improvements in the future.

(I don't want to get involved in the discussion about road holding or drive comfort etc. My comments are solely concerned with the efficiency improvements of the 400h over its coventional equivalents.)

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There is no doubt that getting the most out of a hybrid from an economy point of view takes quite a bit of "learning".

To get best mpg figures you do have to adjust the way you drive.You cannot drive a hybrid exactly the same as a normal car and expect to get best figures.

I get 30mpg mixed driving.I also appreciate that I did not buy an RX400h for economy reasons,so I don't expect great figures,as someone mentioned in an earlier reply official mpg figures are a utopia.

Short journeys where the engine doesn't get up to temperature for long is a real killer for mpg in most cars but particularly in our hybrids.Also cold weather seems to pull economy down to a degree.

I'm into my 4th year of RX400h ownership,and I still find I am adjusting the way i drive,fine tuning.It's a great car,and still enjoying every minute of it.

So,to answer your question,I think 27mpg is probably all right.I certainly remember similar figures,or less,when I took delivery of my hybrid-mainly trying out that instant acceleration courtesy of the electric motors! :blush:

Enjoy,and Merry Christmas :winky:

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