RX 450h - what is a 'normal' mpg return?

pmaskew · May 27

I have a 2010 RX450H that has done 101k. Just recently returned from a trip to Ireland. Did 1005 miles and averaged 35.1 MPG. Mixture of country roads, motorways and some urban driving. 35 to 38 is typical on longer journeys. Tend to drive at 70 using cruise control on motorways. Always have air con on and have Pirelli Scorpions. Around town I average 30 to 32.

More than happy with the MPG. Lets face it 3.5 litre V6 engine.

Sybaris · June 8

On runs to and from the station almost daily and a 20-30 mile run on the weekends I am averaging 28.

But as I am not clocking up mileage at the moment, I only fill up once every 2-3 weeks

Arizona6565 · June 8

On 4/24/2024 at 4:11 PM, StretchedLexuses said:

Hi all,

Apologies that there are existing threads linked to this topic but I wanted to probe what a normal mpg return looks like on UK roads for a gen 3 RX 450h? I got a 2010 with 150k last week and whilst the car is generally very good, I have been a tad disappointed with the mpg. I've not done a long motorway run yet but on some mixed, very careful driving, I'm just about managing 30mpg. With such pronounced effort to be economical, I was hoping for 33mpg. What generally hits mpg hardest in these cars? Can a higher tyre inflation help, e.g. 40 psi? It's got 13 Lexus main dealer service stamps so surely it's well oiled and spark plugs have been changed (i know at least some have from the myLexus app). Ride is a bit choppy and suspect rear bushes have some play but keen to hear people's thoughts. Is 35mpg possible on a long motorway run with controlled speed?

Thanks all...

Well my 22 450h gets about what your getting. The Gas savings come from EV city driving. On the Highway is where you burn more fuel.

GSLV6 · June 9

On 4/26/2024 at 8:13 AM, StretchedLexuses said:

Thanks for the intel. I'm getting 29mpg on mixed driving so far but on the more local and extra urban side (few runs above 50mph). Does make me think that maybe some cells are failing as I've been trying to make the most of engine braking and general braking too, and certainly havent been heavy footed. Feel like I should be getting 32mpg. Spark plugs were last replaced by Lexus main dealer just over 3 years ago. Does a failing 12V battery make any difference? Haven't checked tyre pressures on the 19inch wheels yet but the ride quality is absolutely shocking IMO. Constant vibration and judder with every road contour eliciting a reaction, even on the motorway. I read about the firm ride but this is kind of ridiculous. Rear bushings had an advisory so perhaps that's part of the problem there? Comfortable as the seats are, constant cabin movement grates.

Failing 12V Battery won't affect engine running at all. Why do you think it's failing? 29mpg on this variant is about right for an overall average. You have to be very gentle on the throttle to better 30mpg average, mixed driving. Ride quality wasn't the best on the early RX's...they all pitch and roll a little but thumps and bumps or excessive rear movement does indeed sound like torn bushes. Advisories are usually given when the bushes start to de-bond but are still in place. It's a weak point on the RX. Mine all needed doing by 45 miles despite treating the car with a gentle right boot. Tyres matter on these too. For ride quality, don't over inflate the tyres. Stick with the recommended 33 to 36psi all round. Over inflation especially on worn bushings won't do much for the bushing life or ride quality.

Masiv44 · June 11

On 5/25/2024 at 7:33 PM, MUDGUTS said:

I seem to get the best mpg from V Power.

Is it worth the extra price over standard Ron?

GSLV6 · June 12

19 hours ago, Masiv44 said:

Is it worth the extra price over standard Ron?

It may not be Michael in pure mpg terms. The reason that I use V power though has less to do with mpg and more to do with caring for the fuel system. It doesn't seem to give me more than 1 or 2 mpg more BUT what does make it worth it imho is that it used to have little to no Ethanol present despite the E5 tag, now it uses perhaps 1%, along with the likes of Texaco Super Unleaded. Both these brands use less than most other suppliers. This ensures both slightly more mpg but importantly, it also means a much lower concentration of Ethanol which is both hygroscopic (introduces water from vapour naturally present in the air into your fuel system) and extremely damaging to various plastics and rubber seals as well as leading to accelerated corrosion of some alloy parts. One of my motorcycles had it's fuel system badly damaged by the use of E10 ethanol fuel over several years use which is why I won't use it given a choice.

MUDGUTS · June 12

I’m not sure on the cost/mpg relationship but I feel mine is slightly smoother on any premium fuel and as above it just might help in the longer term. Having said that I’m running on a combination of Tesco Momentum 99 or whatever it is and V Power.

On another note I’ve done two ‘brim to brim’ calculations and both indicated between .7 and 1 mpg BETTER than the trip computer.

Masiv44 · June 12

I'm currently running at 44mpg. I'm going to give VPower a go next fill up.

GSLV6 · June 12

44mpg?! Best combined I can achieve is 36 with average since purchase being 31. I put it down to the number of hills around us and the traffic stop-starts

Masiv44 · June 12

4 hours ago, Masiv44 said:

I'm currently running at 44mpg. I'm going to give VPower a go next fill up.

mOnKeY fInGeRs. That's 34mpg. Mixed driving but mainly local.

GSLV6 · June 13

20 hours ago, Masiv44 said:

mOnKeY fInGeRs. That's 34mpg. Mixed driving but mainly local.

That's more like it!😆

CheshireDriver · June 13

With respect I think a failing 12volt Battery could affect the engine as the dropping voltage will mean that instead of running on the electric motors around town, the engine will be instructed to keep topping up the Battery. This seemed to happen not on my Lexus but my wife's Toyota Yaris Hybrid which has a very similar drive train albeit with only one electric motor. When we first got this car it seemed to be revving all the time, when stationary, and the fuel economy was down a little. Once I spotted the Battery voltage was down and I had to jump start it once, I installed a new 12 volt Battery (Yuasa AGM £130ouch!) and the car suddenly worked better. Better economy and more running on the electric motor. Very economical in fact - now always above 60mpg and usually around 64-66. Not sure if this would apply to a Lexus Hybrid but the principle is similar. The correct 12v Battery to put in my 400h is tricky as the space is not large and the terminals as fitted are the smaller Japanese type. I would really like to put in a 60ah Battery if I could fit it in to give a better reserve of 12V energy. I have got on OK with the Bosch S4022 which is 45aH but the resting voltage is only 12.1volts so I think its days are numbered.

GSLV6 · June 17

The 12v Battery doesn't provide the starting nor any motive power at all. It is purely used as an auxiliary Battery with the main HV hybrid batteries doing the starting and motive power. A failing 12v Battery may not hold a charge so will need replacing or a Battery placed in parallel to start the car to allow the diagnostics (powered from the 12V) and motor control circuit to control the start up via the hybrid Battery circuit. It will make no difference at all to mpg if it was a failing 12v Battery as the charge indicator on the dash is purely for the hybrid Battery. The separate warning of low Battery in the message box indicates auxiliary Battery charge and it's normal for this to shut systems down when it reaches a certain point of discharge, or to trigger other warning messages. It is charged via a rectified charging circuit from the hybrid circuit and the low amperage charge it takes will have no effect on economy.

CheshireDriver · June 17

That wasn't my experience with the Yaris Hybrid. The dropping voltage on the aux 12 volt Battery meant that the DC/DC converter was being powered by the engine runnng more frequently in an attempt to charge the failing aux Battery. It was noticeably revving quite hard when the car came to a stop and would keep revving all the time, so I think it was wasting fuel. Whether it would apply to the Lexus 400h I don't know. It does seem that when stationary the NiMH traction Battery will not charge the 12v aux Battery unless the engine is running (via the DC/DC converter). I think there is also a difference in the N and P settings on the transmission. I believe that the aux Battery is draining when stationary when set to N, and it is better to use P if stopped for any period of time in traffic. Especially if the AC is on as it uses an electric compressor rather than belt driven. The steering is also electric on both Lexus and Yaris hybrid. I think with both hybrid and electric cars, the absence of an alternator means that the 12 aux Battery depends on the dc/dc converter to be sending current from the high voltage traction Battery. A seriously failing 12 volt aux Battery will tend to throw up error codes for this reason especially in electric cars. And there is a fair drain on the Aux 12V Battery from the audio, power steering, AC compressor and lights in both types of car.

GSLV6 · June 17

As mentioned, the 12v Battery failing doesn't, on the RX, affect when the engine kicks in. The charging circuit is powered from the HV NiCad-mH side (you can check the circuit via the workshop manual of you have access to one) I've had two auxiliary batteries fail and neither time when they were on their way out did it make any difference to the main engine running.

brendangeorge · August 1

Hi I regularly drive to the South coast and back (an overnight stay included) and achieve a34/35 mpg. I run on E5 fuel with E10 is drops to 30. I find a constant speed is the secret to lower consumption so I use the cruise control at 70 where I can.
Round town 30mpg is difficult with the stopping and starting.

I keep my tyres at 34psi - I think the ride is a bit hard but it uses less fuel.

I have done 121K miles.

Masiv44 · August 2

Got a best of 37.1 mpg from full to reserve. Two motorway trips, the rest local.

GSLV6 · August 10

Just back from a few weeks in the lake District. Car averaged close on 35mpg on the motorway trip, and best I saw was on a cross-country run of 46 miles (return trip from Ambleside to Ulverston), where it achieved a remarkable 43mpg on mainly A roads. My RX3 at best might have got about 36mpg cross country, so the RX4 is significantly more fuel efficient. Must be the combination of the combined port/direct injection along with beefier batteries and uprated motors; whatever, it's proving to be almost as economical as our 1.8 VVTI Civic!