New rx400h owner. Mpg not good. Cold weather?

[Chrishobbit]

Hi,

I got a 2008 rx400h last week. Im VERY chuffed with it.

However it's proving to be pretty awful on fuel so far.  I've done 180 miles of mixed driving and used 3/4 of a tank. If i apply any more than a feather of throttle, the ICE is kicking in. Particularly today, it's been almost impossible to get the car to drive under Battery power for more than a second or so, even with the engine up to temperature, heater off etc. Is this typical cold weather behaviour?

 

[Romasato]

What MPG does the dashboard show? In winter weather like this I usually get ~26-27 mpg, in summer ~32. Note that fuel gauge will not move at a consistent angle once you're going through your tank, i.e. it is dropping slower through the first half of the tank and faster for the rest of it.

Also, ICE kicks in more readily if heating/air con is ON in any weather. The car has more acceleration power too if aircon is off - but the difference is not easy to notice ;-)

[Gliderpilot]

The ICE does cut in very quickly but I manage 30ish most of the time. I think the control software was changed for the 450h to use more of the Battery at lower speed, but I find that below 30 the Battery will push the car along easily, you just have to be gentle with the throttle.

[Carl911]

To be honest I have found that even with a light throttle in my rx450h engine cuts straight in at the moment.

the only way I can stop it doing it is by switching EV mode on which then holds it in Battery mode longer.

thst said, I'm returning 35mpg start stopping through town and A-roads so I'm pretty satisfied given it's a heavy SUV.

 

carl

[Chrishobbit]

Quick update,

Filled up with 250 miles on the clock today and worked it out at 22mpg overall. Currently showing 25 on the trip info, but I reset that about 80 miles ago.

Had much more use of Battery power driving today as it was warmer when I left work at lunch, so I'm convinced this is a major factor. In fact, i took my mum shopping  and drove the 2 miles from her house to the supermarket completely without ICE.

I'm not actually that bothered about the mpg, but I'm interested in the technology, and, of course, the health of the car I've just bought.

I'm thinking some old fashioned ideas, like covering half the rad, may help at this time of year.

[royoftherovers]

A few well known facts Chris;

1. The warmer the temperature the better the fuel consumption

2. The colder the temperature the worse the fuel consumption

3. The wetter the weather, the better the car seems to go 

4. The OBC electronic consumption needs to be reduced by about 5% to equate to brim to brim consumption 

Forget about blanking off the radiator and just enjoy the dream you are driving!!.

 

Regards

John

[Gliderpilot]

I wouldn't even consider putting anything in front of the radiator because not only does it cool the engine bit it also cools the inverter and associated electronics which don't like getting warm. Plus the gearbox cooler is also at the front.

[Assa1974]

When I first got my car last Easter I was dissaponted with the fuel consumption and didn't feel the batteries were doing their job. After a bit of research I found that you could 'reset' the Battery levels and control system. After that there was a definite improvement in the mpg and only a couple of weeks ago I achieved my best ever run of an indicated 34.7mpg over my 100 mile journey to work. My conclusion is that by far the biggest factor impacting fuel consumption is my right foot and it's taken a concerted effort to alter my driving style to achieve what I would term 'reasonable' economy.

[JBPRX400h]

Hi Chris

It might be worth trying the ISC (idle speed control) learning procedure.  It certainly worked when we had an RX400h.

http://us.lexusownersclub.com/forums/topic/58930-isc-learning-procedure-without-lexus-diagnostic-tester/#comment-379201

Good luck

JBP

[jabowsi]

Just thought I'd share this one, a 170 mile trip from London to sheffield.

[JBPRX400h]

Glad to see you weren't breaking the speed limit, but how did you manage to take the photo?

JBP 

[Romasato]

49 minutes ago, JBPRX400h said:

Glad to see you weren't breaking the speed limit, but how did you manage to take the photo?

JBP 

Well, obviously by not texting while driving! 

[jabowsi]

Hands free chest phone holder with voice activation photo taking using Siri! Obviously. ;-)

[jabowsi]

This was a trip from Sheffield to Kings Lynn and back, mostly A and B roads. 217 miles mostly in the rain and I don't think the MPG is bad at all.

[Assa1974]

Not being in any hurry to get to work yesterday I decided to have a little experiment. I was travelling late morning so the motorway was clear. I cruised along at a steady 65mph and over my 110 mile trip into the office the car recorded the mpg as 33.2. Coming home last night after the rush hour, so basically thr same traffic conditions, I cruised at 70mph. Take into account the colder temperature if 6 degrees compared to 13 degrees in the day... my average mpg came out as 32.5. I am surprised firstly that either run was as low as these readings given the conditions on the road and average speed, and that there was such little difference between the two. My conclusion is that even over a reasonably long run small things like having to brake then re-accelerate just a few times or put your foot down hard to over-take someone quickly has a big impact on your over-all fuel efficiency. Hardly scientific I know but thought it was interesting.

[Hitby]

Pulling a small caravan for the first time gave me quite a shock when I got home 

 

[royoftherovers]

No surprise there DAN as your towing package represents the aerodynamics of a brick pulling a horse !  ;) ;);)

 

Regards

John

[JBPRX400h]

Wind direction can make a considerable difference as well.  We have noticed driving down through France on a regular 400 mile journey different fuel consumption when outside temperature, speed etc have all been similar but with a north or south wind.

JBP

[royoftherovers]

20 hours ago, royoftherovers said:

No surprise there DAN as your towing package represents the aerodynamics of a brick pulling a horse !  ;) ;);)

 

Regards

John

Seriously Dan, a really effective way to optimise fuel consumption in a Hybrid is to cruise for as long as possible and where circumstances permit, with your foot OFF the accelerater. You are effectively coasting but still in full control of the vehicle and not using any fuel at all !

Regards

John

[Carl911]

I know slightly

off topic but I have both rx450 and gs450 so both have same engine although it's slightly de tuned to make the RX slightly more economical.  

So despite the RX Being heavier and less aero dynamic it still manages to be about 6-8mpg more economical than my Gs.  All things considered I think that's pretty good.

that equates to about an extra 80miles per tank.

carl

[cachaciero]

I have owned a 2007 RX 400H for about three months now as regards fuel consumption it is a bit of a mixed bag. On a 300+ round trip from Sussex to Bristol I can get 36/37 consistently driving on or slightly in excess of the limits, locally around town short journeys 20-25.

When I first had the car I noticed that even stopped in park the ICE appeared to run quite a lot, much more than the Prius.  Cutting a long story short I replaced the 12v Battery after which the ICE ran a lot less when stationary. The 12V Battery is charged from the inverter so if there is a constant drain on the 12V side the Main Batteries will also be discharging resulting in the ICE cutting in much more frequently. My impression is that the 12V management software in the inverter side is not as clever as I would expect it to be. (And the Battery is not the right kind of Battery or in the right place  for the job it has to do which is in part the reason it seems to give many people problems)

The ICE gobbles fuel when cold and I have noticed that starting and running the engine from cold seems to have a disproportionate effect on fuel consumption. Basically if a lot of your miles are going to be start from cold drive two miles to Supermarket / School /Station whatever, let it get cold prior to doing the return trip fuel consumption will not be good!!. 

My feeling is that the Hybrid Transmission Software is not particularly well optimised for this car and that the ICE kicks in far to early in many circumstances i.e the Battery side is not being used anywhere near as much as it could be. (The Prius seems far better in this respect)

My techniques for maximising fuel consumption.

1 Set cabin temp to low at engine start (to minimise ICE running just to provide heat)

2 Set the Aircon compressor off unless you really need it. (Not sure just how well this is managed but it has the potential to consume a fair amount of power unnecessarily)

3. Remember gentle braking equates to energy recovered back into the Battery heavy braking equates to well polished disks and energy wasted in heat.

4 Try and keep the traction Battery as fully charged as possible by using the B position when appropriate. (3 and 4 should be thought of together :-)

5 Keep the power meter as close to 0 as you can or even better deep into the blue sector :-)

 

Having said all that taking into account it's running on cheaper fuel it's no worse that the 2.2 auto diesel estate it replaced and there isn't all the exhaust filter additive stuff to worry about :-)

Oh! almost forgot the Prius fuel consumption is reckoned by many to be sensitive to both tyre and tyre /tread design and tyre pressure, certainly when I first owned it with summer tyres a few PSI over normal  to improved the fuel consumption, after fitting all weather tyres the fuel consumption dropped a little and variations in pressure seemed to make less difference (but still positive).

I have taken the same logic to the RX and run with 5 psi more in each tyre than recommended I mention that because all my mileage figures quoted would have been achieved with these tyre pressures.

 

Edited November 20, 2016 by cachaciero
Accuracy

[Glover]

My 450h is all over the place at the moment as well.  Averaged 43mpg on a 50 mile trip with mixed town and A & B roads rolling hills and a couple of steep ones but earlier in the week I was getting 32-33 mpg just city driving. Both trips with ICE, heating and electric seats on all the time and lights and wipers some of the time.  Overall average for the 6,500 that I've done since getting the car is 37.5. 

I get far better mpg with the energy monitoring display on; it  helps with training my right foot to cruise!  In the summer I was getting 38 - 40mpg with a best of 45.1.  My driving is a combination of city commute (in the summer city only would average 38 so 5 or 6 mpg worse at the moment), and on odd days rural A & B roads with the odd dual carriageway or motorway.  I don't go mad just keep up with traffic so generally 50-60 on A roads and 70 on dual carriageways.

One thing I'm not sure about is whether air con is on still a bit confused about that function as there is a recirculation light, another light next to it on the left had side and then an auto button with light under it on the right hand side.  Which button or buttons activate the air con?  Plus I don't know if they all do this but mine seems to start up with the mode on feet only regardless of the previous setting.

[Glover]

Just realised guys I probably don't know what ICE is.  I thought In Car Entertainment but I assume as it kicks in that it's something totally different.

[NemesisUK]

Internal Combustion Engine?

[Glover]

Thanks Nemesis, that makes perfect sense. Mine sometimes shows an almost full Battery and then will cut in when I'm doing slow speed manoeuvring but at other times will stay on electric when it's showing two purple bars and I'm doing over 30!  But the technology is amazing; this is my first hybrid and although I know when it's cutting in at very slow speeds, once its going it's so seamless and quiet that unless I have the energy monitor on accelerating hard I struggle to identify what motor is working.  Lexus certainly know how to build cars.