Rx 450H Fuel Consumption

[Intricateweb]

I've had five RX's over the years and generally more than happy. I did have a dicky 350 (bad fuel consumption <20mpg) and ended up trading it in for a 400h after three months which served me very well for 85k and five years.

I bought a new 450H on the basis on better consumption and more power. However it is averaging 30.8mpg over 10k against the 400h 's 32mpg despite being driven with carpet slippers.

The garage don't know what to do about and seem to think this is a common problem. On top of that it is much slower , apparently down to the rebalancing of power between front and rear axles which avoids a steering problem with the 400h.

All in all I am quite dissatisfied with the situation, especially as I still have access to the 400H and it continues to delight. Any solutions??

[noby76]

come on intricateweb its only 2 miles per gallon difference between the two cars.. i think RX400/450h fuel tank holds a total of 65 litres (14.3 gallons). if you average 30mpg in the RX450h you will travel a total of 426miles on a full tank... if you averaged 32mpg in the RX400 you will travel a total of 457miles from the same full tank. now thats a difference of 31 miles between the two cars which is roughly the miles the RX450h does to 1 gallon. petrol is sold at 1.34p per and 4.54 litres makes 1 gallon so this works out at £6 for the extra 31miles needed to travel in the RX450h to meet RX400's total of 457miles. I dont think an extra £6 for a full tank will break the bank although i agree it does add up over a year.

worth checking your tire pressures as sometimes a lower tyre pressure cases the engine to work slightly more than it should to move the car I know some car owners drop thier tyre pressure for a bit more comfort but that could affect mpg slightly. you could also get rid of excess weight i.e stuffs in the boot you dot really need for your daily journeys and roof rack thats if you have one. I personally will chuck in the extra 6 quid and enjoy the car for what it is :) . hope this helps.

[HASSELBLAD]

I've had five RX's over the years and generally more than happy. I did have a dicky 350 (bad fuel consumption <20mpg) and ended up trading it in for a 400h after three months which served me very well for 85k and five years.

I bought a new 450H on the basis on better consumption and more power. However it is averaging 30.8mpg over 10k against the 400h 's 32mpg despite being driven with carpet slippers.

The garage don't know what to do about and seem to think this is a common problem. On top of that it is much slower , apparently down to the rebalancing of power between front and rear axles which avoids a steering problem with the 400h.

All in all I am quite dissatisfied with the situation, especially as I still have access to the 400H and it continues to delight. Any solutions??

Hi there, It does seem quite strange and I would be suspicious of what the dealership is saying.

Assuming that you have cleared extra weight, tyre pressures, types of petrol and your computer accuracy out of the way.

My 400h was definitely poorer on economy than my 450h.and by quite a bit!

It is true that by changing axle loadings during hard acceleration that the 'twitch' of the 400h has been eliminated but there is no performance degradation. My Race Logic data logger puts both cars at almost spot on 7.2 secs up to 60.

There are a couple of genuine enhancements on the Atkinson cycle engine (the 400h is on an Otto cycle unit) that help considerably with consumption and particularly so in cold weather. One bleeds a little hot exhaust gas into the mixture during warm up and the other uses exhaust heat to warm the engine block up quickly.

If one or both of these are malfuntioning then your mpg would suffer.

Otherwise, have the car checked for BHP on a four wheel drive rolling road and see if it satisfies the near 290bhp claimed.

One small question, is your car the 450h with the 'spindle' grill?

[DanD]

I wonder... would you also expect a noticeable difference in consumption depending on the type of unleaded used?

[Duncan Roberts]

I wonder... would you also expect a noticeable difference in consumption depending on the type of unleaded used?

My experience suggest that cheap petrol can give you worse consumption than that of the major brands. I first found it in my first RX300 (improved from 16 to 20mpg) with BP petrol, and my current RX400 performs less well on cheap petrol. Curiously 97 RON petrol offers little benefit as a trial demonstrated.

[HASSELBLAD]

I wonder... would you also expect a noticeable difference in consumption depending on the type of unleaded used?

Hi Dan,

I have only ever used regular 95 Ron in my 400h and now my 450h. My 400h was at least 10% less economical than the 450h and in some road conditions it was returning considerably less. Nevertheless, for its size and performance it was excellent!

The 450h is a larger car but does enjoy some very significant energy saving design improvements. I find they work admirably but you are not the first to have difficulty exploiting them.

I still suspect that your car is failing somewhere and I would check on a rolling road for overall performance and then have Lexus confirm the two start up systems are definitely doing their job. The 400h did not have these.

I have just come in after a 110 mile trip at mostly very busy motorway speeds, heavy commuter traffic and quite a bit of stop/go queing.I still averaged 35mpg and that is quite poor for this car. My tyres are at 35psi cold and it was 95 RON fuel.

Have you checked your computer? My 450h reads 1mpg high and my 400h was 1.5mpg high. They can also read low.

You didn't say if your car has a 'spindle' grill? If not, then all the above is valid.

[DanD]

Thanks HASSELBLAD. I think your response should have been directed to Intricateweb who I am sure will also be interested in your comments.

My question was more of a general interest, and my comments below are not aimed at this post in particular, but all posts related to pertol consumption.

My car averages 28.5 mpg. I am not particulary careful in my style of driving, have the aircon on all the time, etc, etc, and I am not overly concerned about fuel consumption so long as it does not drop below 28mpg. It does amaze me that some people have managed to achieve low 30's, but I have no interest in spoiling my enjoyment of a brilliant car in trying to beat this... although I admit that, in the right conditions, it can be fun to watch the info screen and see 99.9MPG on the display.

Having said this, I have found the various entries on fuel consumption fascinating: it is interesting to see and understand the various factors that may influence consumption such as the obvious like driving style, and the less obvious like type of fuel, typre pressure and others.

I think that, at the end of the day, it is difficult to make effective comparisons between cars and rivers because there are just too many unknowns. Ratio between urban and motorway driving, short vs long journeys, flat or hilly environment, weather, aircon on or off, number of passengers, number of electrics switched on (wipers, lights, phone or other chargers), how long since the car was last serviced, condition and inflation of tyres, etc.

I suspect that, as the winter closes in, a lot of us will see consumption worsen as our cars will be relying on their petrol engine more and for longer to warm up.

Given all this (and more!), I think that a variance of several miles per gallon is perfectly acceptable. The RX400h/RX450h are big, heavy cars full of gadgets. They will always struggle to compete - from a consumption perspective - with similar sized diesels, but will always be more economical than their petrol competitors. Personally, I bought my car because of its comfort, reliability, and the reputation of Lexus dealers (at least my dealer!). If low petrol consumption had been my priority, I would have looked elsewhere.

[Greyanglia]

Out of interest what is the significance of the 'spindle grille'?

[HASSELBLAD]

Out of interest what is the significance of the 'spindle grille'?

Hi there, only a personal one.

I never quote actual figures or make comments on a car that I have not had detailed experience with.

My RX is not a 'spindle grille' and whilst Lexus say there are only very minor cosmetic differences, I prefer not to assume that the cars are mechanically identical.It does,however, seem that they are.

I did use a 'spindle' F Sport for a day and clocked up a goodly mileage and still averaged 36mpg----------so, it does seem that Lexus is, as ever, telling the truth.

No more than that but many thanks for asking.

[Greyanglia]

See what you mean now!

I also had a brand new demo for the day amd I was pleased to see the mpg was no better than mine at 30 ish to the gallon. The differences only seem to be the grille and inside a couple of really minor differences that were different but not necessarily better. The centre box lid opens to 90 degrees which is good and the layout in the storage box is improved. The slightly thicker steering wheel with the EV button easily accessible is better but that's a personal preference and clicking the mouse in a different way is neither here nor there.

I think the only mechanical difference is with the F Sport which gains a small tweak in bhp plus 'sport' like goodies. So all in all as a private buyer I am pleased that it should not knock the residuals as much as a major facelift can do.

If it ain't broke etc etc!

[bogeyBogeybogey]

Hi,

I am getting 33.4mpg averagefrom my 450h which i think is pretty good.

My driving I would say is on the careful side of average generally sticking around the speed limits and being as smooth as possible.

Seems to be quite a variance in the consumption from the reports on here

[HASSELBLAD]

Your 33.4mpg is good and compared with many non-hybrid cars, it is excellent.

The reason for the wide variance in consumption figures has been explained on the Forum many times but one unrecognised major reason, is that of how the Hybrid works.

If you simply charge everywhere and slam the brakes on hard, you will be little more than a 3 litre+ petrol car. Still a lot more economical than a petrol Range Rover or Discovery (15 to 20 mpg) but way off what a Hybrid can really achieve.

Use the 'scavenging' abilities of the 400h and 450h and you can, on the right roads, get double the best from non Hybrid cars of a similar size and spec.

The choice is yours.

Some might say that they bought the Lexus to enjoy it and that is valid enough. But once bought, the major 'controllable' expense is petrol. For a great many drivers that is very important and the reason why it is well worth fully understanding and then exploiting what the Lexus Hybrid has to offer.

I can get remarkable mpg figures out of mine! I am delighted.