Rx450H Gas Mileage

[smitty49]

I recently purchased a 2012 Lexus RX450h, locally i get about 28 miles a gallon which is mostly highway driving. On a long trip over 1000 miles (driving all day long) using the cruise control on major hgihways and going about 70 MPH my gas mileage starts out at 28 and each tank on that drip drops down by about 2 miles per gallon when I refuel, by the end of the day i am down to 22 mpg. I have done 3 trips like this and the results are always the same. When the car sits overnight and i resume driving the next day the first tank will be 28 and each refill that day the mileage will decline. I have had the car into Lexus and they can't find anything wrong and say this may be normal.

I also have a 2012 Lincoln MKZ hybred and on the same trip (same roads, speed etc) i consitently get 38 mpg

Any ideas what could be wrong ????

[katzjamr]

my car is a 400h however i can say that 70 mph (a speed i often use) does not give the best mpg on the highway.

if you can stand it, do that same longer trip at 55 to 60 mph with the cruise control set, i will bdet money your mph will be better. anything above 60mph on the freeway (unless its all downhill, like a mountain road) cuts down on mpg, the ICE runs much more than normal to keep up the speed. also premium fuel will give you better gas mileage, at least on the 400h, and warmer weather is also more efficient for the hybrid battery i.e. better gas mileage in warmer weather. Also in seattle i am able to get 3mpg better mileage when i turn off the AC.

[smitty49]

thanks, I am using premium fuel 93 octane and I am driving between Dallas and south Florida, the weather was warm on all 3 trips I did.

[The G Man]

The MPG computer always starts out high and as it takes more sample, it gets a more accurate reading. Try doing the MPG calculation by hand, its much more accurate.

[jaswood]

For ONLY hwy driving 22 MPG for the RXh would be about right.

Hybrid cars have no advantage if there is no opportunity to regain energy for FREE, energy that would otherwise be lost as HEAT through braking, friction or compression. Actually hybrids are at a distinct disadvantage, in your case an actual RX350 would likely get greater FE by 2-3 MPG on that same trip.

The disadvantage arises from the fact that every time you accelerate or "pull" up an incline, the extra torque required will be supplied by relying on the electric motor torque. In doing so the HV battery SOC will decline and the only method available for recharging it will be to slightly elevate the ICE output torque for relatively long periods of time. Highly "lossy" procedure, that.

[jaswood]

I recently purchased a 2012 Lexus RX450h, locally i get about 28 miles a gallon which is mostly highway driving. On a long trip over 1000 miles (driving all day long) using the cruise control on major hgihways and going about 70 MPH my gas mileage starts out at 28 and each tank on that drip drops down by about 2 miles per gallon when I refuel, by the end of the day i am down to 22 mpg. I have done 3 trips like this and the results are always the same. When the car sits overnight and i resume driving the next day the first tank will be 28 and each refill that day the mileage will decline. I have had the car into Lexus and they can't find anything wrong and say this may be normal.

I also have a 2012 Lincoln MKZ hybred and on the same trip (same roads, speed etc) i consitently get 38 mpg

Any ideas what could be wrong ????

Your MKZ not only weighs less than your RX but also has a relatively small Atkinsonized 4 cylinder. The MKZ may have been updated to DFI as of 2012.

[lemon]

For ONLY hwy driving 22 MPG for the RXh would be about right.

Hybrid cars have no advantage if there is no opportunity to regain energy for FREE, energy that would otherwise be lost as HEAT through braking, friction or compression. Actually hybrids are at a distinct disadvantage, in your case an actual RX350 would likely get greater FE by 2-3 MPG on that same trip.

Not according to www.fueleconomy.gov which shows the 2012 RX450h AWD at 28 on the highway vs 24 for the 2012 RX350 AWD.

[lemon]

The disadvantage arises from the fact that every time you accelerate or "pull" up an incline, the extra torque required will be supplied by relying on the electric motor torque. In doing so the HV battery SOC will decline and the only method available for recharging it will be to slightly elevate the ICE output torque for relatively long periods of time. Highly "lossy" procedure, that.

You know there is an internal combustion engine in a hybrid that can output more torque for climbing an incline JUST like a regular non hybrid vehicle. The extra torque does not ONLY have to come from the electric motors. The THS computer does a pretty good job of figuring out which one will be more efficient in any given situation.

[smitty49]

my only point was Lincoln says it should get 38MPG on the highway and it does, Lexus says 28 and it doesn't

I recently purchased a 2012 Lexus RX450h, locally i get about 28 miles a gallon which is mostly highway driving. On a long trip over 1000 miles (driving all day long) using the cruise control on major hgihways and going about 70 MPH my gas mileage starts out at 28 and each tank on that drip drops down by about 2 miles per gallon when I refuel, by the end of the day i am down to 22 mpg. I have done 3 trips like this and the results are always the same. When the car sits overnight and i resume driving the next day the first tank will be 28 and each refill that day the mileage will decline. I have had the car into Lexus and they can't find anything wrong and say this may be normal.

I also have a 2012 Lincoln MKZ hybred and on the same trip (same roads, speed etc) i consitently get 38 mpg

Any ideas what could be wrong ????

Your MKZ not only weighs less than your RX but also has a relatively small Atkinsonized 4 cylinder. The MKZ may have been updated to DFI as of 2012.

[smitty49]

Thanks and I agree the Lincoln is lighter, my only point was that Linclon says the car should get 38 MPG on the highway and it actual does get what they advertise and Lexus says it should get 28 MPG and it doesn't get anywhere near that on a long highway run

[jaswood]

The disadvantage arises from the fact that every time you accelerate or "pull" up an incline, the extra torque required will be supplied by relying on the electric motor torque. In doing so the HV battery SOC will decline and the only method available for recharging it will be to slightly elevate the ICE output torque for relatively long periods of time. Highly "lossy" procedure, that.

You know there is an internal combustion engine in a hybrid that can output more torque for climbing an incline JUST like a regular non hybrid vehicle. The extra torque does not ONLY have to come from the electric motors. The THS computer does a pretty good job of figuring out which one will be more efficient in any given situation.

"...there is an internal combustion engine in a hybrid..."

Yes...but.

That is an Atkinsonized IC engine that sacrifices, in favor of improving FE, about 30% of the torque level an engine of that displacement volume would normally produce. Thus a 2L engine acts like a 1.4L. Think of the electric as "turbocharger" used to raise the overall torque level back up, in most cases even beyond a 2L ICE level.

"....The THS computer does a pretty good job..."

Well, yes...and no.

These hybrids need, desparately so, a "mode" switch (shades of Edson DeCastro). They need a way that would allow the driver to "tell" the THS computer that "for now" there will be little or no opportunity for recovering "FREE" energy. The THS, as a result of being in this new highway "ECO" cruise mode would avoid use of the hybrid battery SOC except for extraodinarily deep depressions of the accelerator pedal.

So with cruise control enabled there would be NO use of the SOC for normal "re-acceleration" rates. In reality cruise control enabled could be used as the "switch" to highway "ECO" mode.

"...engine...can output more torque..."

Yes, exactly my point....

Yes, but if the battery SOC is high enough then it is much more fuel efficient to make use of that SOC rather than asking the ICE to produce that extra level of torque.

Only the driver has the knowledge required for the "understanding" of FE "futures", so now the thing that is required is a way to convey that knowledge to the THS computer.

[The G Man]

Putting aside the technical Mumbo jumbo, the cold hard facts remains that the RX hybrid gets 12 % better gas mileage than the RX350 on the highway. One must really have a good understand of how the Lexus hybrid system work before making any conclusion. The Lexus hybrid system is a parallel system meaning the electric motor can run at the same time as the ICE, therefore, help to increase gas mileage, even at high speed.

[lemon]

Yes, I forgot that the 450 uses an Atkinson cycle ICE. Whether the THS functions differently because of that I don't know.

What I can tell you is that in my 400h, driving on the highway and watching the hybrid display in the NAV screen, I've seen (many times) the power flow from the ICE to the front electric motor completely bypassing the battery. So in that case there would be no need to run 'elevated' to bring back up the SOC of the traction battery as the traction battery was not being used to power the front electric motor. Also, in that case the ICE is not creating the additional torque directly, it is powering the electric motor and that is producing the additional torque.

All I can say is that my 400h gets better gas mileage on the highway than a 330. Does it match the EPA (or in my case Transport Canada) stats? No, but not many cars, hybrid or not, do.

[jaswood]

Yes, I forgot that the 450 uses an Atkinson cycle ICE. Whether the THS functions differently because of that I don't know.

Insofar as I am aware an Atkinson cycle engine and the (HSD) THS functions are mutually INCLUSIVE.

What I can tell you is that in my 400h, driving on the highway and watching the hybrid display in the NAV screen, I've seen (many times) the power flow from the ICE to the front electric motor completely bypassing the battery.

Yes, absolutely. At common highway cruise speeds on reasonably flat terrain the ICE torque level, eve derated via the use of the Atkinson cycle, is more than adequate.

So in that case there would be no need to run 'elevated' to bring back up the SOC of the traction battery as the traction battery was not being used to power the front electric motor.

Granted, my direct expereince is only with the first generation Prius, but what I found was that with even the slightest level of need to accelerate, even with the slight speed excusions below the CC setting, the battery would be called up for that "extra".

Also, in that case the ICE is not creating the additional torque directly, it is powering the electric motor and that is producing the additional torque.

With the exception of the word "additional" Agreed, absolutely.

All I can say is that my 400h gets better gas mileage on the highway than a 330. Does it match the EPA (or in my case Transport Canada) stats? No, but not many cars, hybrid or not, do.

What I was, have been, trying to point out is that the THS system ALWAYS operates as if there will be upcoming opportunities to regain HV battery SOC via the need for braking or during "coastdown" (simulation of engine compression braking using the power generation capability.

My experience has been that traveling on the highway, say with CC set, the THS system will make use of the SOC for even minor levels of (re-)acceleration. It will do so until the SOC reaches enough of a low point that the THS begins the "default" recharge method, the ICE. Once instituding the default recharge method it will now remain in that mode until a reasonably higher SOC is reached.

On a drive from Seattle to Portland, ~145 miles, I see it repeat that cycle numerous times.

It is for that reason that I suspect better highway FE could be attained if the system could be "told", in advance, that there will be NO future free energy recovery opportunities in the near term, so bias the reacceleration torque needs toward the ICE.

[jaswood]

Yes, I forgot that the 450 uses an Atkinson cycle ICE. Whether the THS functions differently because of that I don't know.

What I can tell you is that in my 400h, driving on the highway and watching the hybrid display in the NAV screen, I've seen (many times) the power flow from the ICE to the front electric motor completely bypassing the battery. So in that case there would be no need to run 'elevated' to bring back up the SOC of the traction battery as the traction battery was not being used to power the front electric motor. Also, in that case the ICE is not creating the additional torque directly, it is powering the electric motor and that is producing the additional torque.

All I can say is that my 400h gets better gas mileage on the highway than a 330. Does it match the EPA (or in my case Transport Canada) stats? No, but not many cars, hybrid or not, do.

My '01 "awd" RX300 gets 22-23 MPG, consistently, traveling the 800 miles to central MT from Seattle, 70-80 MPH once out of WA. Most reports of RXh FE seem to be about the same.

[cduluk]

The Rx400h doesn't (in real life- not according to the numbers Lexus provides) do any better on the highway than the all-gas version. It's only in the city that it does better as the electric motors give the engine a break more often. At high speeds the electric motors hardly ever kick in (you'll notice this if you look at the energy monitor). So basically on the highway you're running on a 3.3L engine similar to that of the Rx330 yet it's carrying the extra weight of the hybrid components...

[The G Man]

Lexus made some improvment in the RX450h, instead of the RX400h's 25 MPG on the highway, it is now 28 MPG for the RX450h. We can pretty close to 28 MPG if we drive around 65 MPH.

[cduluk]

I'd still take the Rx400h's quicker acceleration and passing power. I've driven the 2010+ Rx450h and it is quite less energetic than the Rx400h, something i wouldn't trade for a few mpg.

[The G Man]

2012 RX450h, 0-60 in 7.5 seconds and the 2007 Rx400h, 0-60 in 7.2 sec. Not as much difference as you might think. Again, both numbers are from Edmunds. Sometimes a car can make you feel like you are accelarating faster.

[cduluk]

It all depends on how energized the hybrid battery is. When the energy monitor indicates the charge to be in the "green" there's a great deal more power than when it's in the low "blue" range. Although very noticeable on the Rx400h, i haven't found there to be any difference with the RX450h's power no matter what battery charge level, nor what driving mode it's set in. It feels like the RX450h's energy distribution is more "controlled" than it is on the Rx400h. Driving the two, you can really feel the "power" bursts with the Rx400h but not so much with the Rx450h. It's obvious Lexus is limiting the power from the engine and electric motors on the new model, most likely in an effort to save more fuel.

[jaswood]

It all depends on how energized the hybrid battery is.

No, that's not it. The difference in accelleration between the RX400h and the RX450h is the result of the RX450h's V6 engine being converted to the use of the more fuel efficient but lower torque ATKINSON cycle.

When the energy monitor indicates the charge to be in the "green" there's a great deal more power than when it's in the low "blue" range. Although very noticeable on the Rx400h, i haven't found there to be any difference with the RX450h's power no matter what battery charge level, nor what driving mode it's set in. It feels like the RX450h's energy distribution is more "controlled" than it is on the Rx400h. Driving the two, you can really feel the "power" bursts with the Rx400h but not so much with the Rx450h. It's obvious Lexus is limiting the power from the engine and electric motors on the new model, most likely in an effort to save more fuel.

Paragraph beginning with Dave Hermance down the page.

http://www.familycar.com/RoadTests/LexusRX400h/

....

[cduluk]

It all depends on how energized the hybrid battery is.

No, that's not it. The difference in accelleration between the RX400h and the RX450h is the result of the RX450h's V6 engine being converted to the use of the more fuel efficient but lower torque ATKINSON cycle.

When the energy monitor indicates the charge to be in the "green" there's a great deal more power than when it's in the low "blue" range. Although very noticeable on the Rx400h, i haven't found there to be any difference with the RX450h's power no matter what battery charge level, nor what driving mode it's set in. It feels like the RX450h's energy distribution is more "controlled" than it is on the Rx400h. Driving the two, you can really feel the "power" bursts with the Rx400h but not so much with the Rx450h. It's obvious Lexus is limiting the power from the engine and electric motors on the new model, most likely in an effort to save more fuel.

Paragraph beginning with Dave Hermance down the page.

http://www.familycar...ts/LexusRX400h/

....

I was referring to the 0-60 time of the Rx400h, which can vary depending on how charged the hybrid battery is. If the battery is "fully charged" the car delivers more power, however if the battery is low, the acceleration is much worse... There really should be two 0-60 times for the Rx400h; full battery which i'd guess is in the 6.7sec range and low battery which is in the 7.6sec range. I'm not even kidding when i say it's that noticeable...

[smitty49]

latest from Lexus, they stated Lexus does not say the car should get 28 MPH highway the EPA does, they said getting 2-23 on a long trip is normal not what I expected to hear from Lexus

[The G Man]

Unfortunately, poor gas mileage is not a warranty item. We get 29 MPG in the summer on the highway consistantly. Many variables can affect gas mileage, wind, winter gas, incline tire pressure or tires.

[The G Man]

I was referring to the 0-60 time of the Rx400h, which can vary depending on how charged the hybrid battery is. If the battery is "fully charged" the car delivers more power, however if the battery is low, the acceleration is much worse... There really should be two 0-60 times for the Rx400h; full battery which i'd guess is in the 6.7sec range and low battery which is in the 7.6sec range. I'm not even kidding when i say it's that noticeable...

The RX450h's battery management is a bit different, I have never seen the batteries drain down in my RXh before. Most of the time its full or 1 bar below full.

The RX400h is a bit quicker than the RX450h, but its not a full second faster to 60 MPH. The RX400h is a lighter car, it can give you the affect that it is going faster than it really is. For example, when I test drove the Lexus CT200h, that car felt fast, it felt a lot faster than the 0-60 time of 10.4 sec. as tested.