We are a 3 week old owner of a used 2006 rx400h (39k miles).

We just took our first 4 hr round trip drive with the car (freeway) and I feel like the car is in "engine recharging batteries" mode way too often.

We are on the freeways (speed limits 65 or 70) for the entire trip going about that speed. The battery indicators shows that it's 8/10 full and NEVER shows the top 2 bars charged EVER. I understand that the batteries are charged/drained only between 20%-80% levels or something like that for longevity. Fine. But during the whole trip, unless it was downhill, the engine was always charging the batteries.

This did not make sense to me since it would seem that the efficient use of the hybrid technology for this trip would be to use the batteries to do electric motor assist to the engine to drive the wheels... until the batteries drained to a certain level then let the downhill charge the batteries. Instead, it's using extra fuel to keep the batteries topped off! This seems stupid! And the indicator showed average mpg of 22-23mpg for the trip. For the SAME trip, when we used our previous car (2004 RX330) we would get 24mph!!! That means the hybrid did WORSE!

Does this seem right? Is there something wrong with our car?

Chim, that is normal for the display and charge condition. You will rarely see 100% charge and never cruising at 70 mph. Wind resistance is not your friend.

The RX400h is not a great road vehicle; better in the city as with all hybrids. The revised EPA for your car is 27 mpg city and 25 mpg highway so you did about what was promised.

I have done as little as 19 mpg on a road trip with a strong headwind running 80 mph.

Tom

Yep, normal. The hybrid battery is never supposed to be 100% charged.

Yeah, I understand that. But why isn't there electric assist during cruising, even at 70 mph?

Especially if the charge reaches the 80% level and really isn't going to charge more, then why not use the stored power to help with the cruise?

Particularly in this trip, I'm going over large hilly freeways, which means several opportunities to recover some downhill energy to assist with the uphill.

The electric assist is typically used while accelerating, especially up a hill. While cruising, there is very little load on the engine, thus, no need for "boost". You will find that on highway cruises, there is virtually no difference in mileage between an RX400h and RX330 or RX350. However, around town, the RX330/RX350's fuel mileage will plummet to 16 MPG or so. The RX400hs mileage around town is 28-30 MPG, almost double that of its non-hybrid siblings. We average about 25 MPG for combined city and highway. It is unlikely that any non-hybrid RX will achieve that kind of mileage under the same conditions.

What he said...the electric motor has a lot of torque that helps in acceleration but isn't much use when cruising.

Also bear in mind the car doesn't really know what kind of road you're on, that its going to be a hilly one with opportunities to recharge the batteries.

Maybe you guys didn't see this part of my post:

You weren't accelerating up the hill. You were driving on a highway that included uphill grades. The car doesn't know you're on hilly roads...it knows that you're traveling at constant highway speeds...thats all it knows.

The hybrid system is a low speed benefit...not a high speed benefit.

Are you interested in our expertise in this area or just arguing with us?

I'm interested in finding an understanding for my situation and an appropriate solution.

I read the responses 2-3 times and tried to consolidate it with what I knew of my situation and what I had posted, and there seemed to be a disconnect, hence my reply. And even with your latest reply, there are things that don't seem to jive... maybe it's me, but it's still not consolidating.

The car may not "know" I'm on "hilly" roads, but it *does* know that the load has suddenly gone up without additional throttle application. In fact, I was on cruise control much of the time to try and let the car sort it out. From what I can see it would seem that with the increase in load and above the "full" threshold charge, the most efficient use of the the stored electric power would be to do electric assist of the combustion engine, not further weigh down the combustion engine by trickle charging the batteries.

chimchim, when toyota did research on hybrid cars prior to the first 400h they found that Lexus owners at that time had two major concerns, first they didnt want to give up luxury for the hybrid experience, and two they didnt want to worry about the battery. Toyota knew at that time the our batteries would last longer if they were never fully charged or depeleted say beyond the last 30 or 40% of their charge. So the algorithm that maintains this range was set up to protect the battery in that way and toyota could give you a seven year 100k hybrid warranty (longer in california). Some of us wish the charging system was more adaptable and there have been improvements in the later models however until the next generation battery is available this is the way its going to be. There really isnt any way to change how the 400h decides when and where to charge or discharge the battery. also keep in mind everything is running off the main battery once the car is started, so the drain of accessories, the need to keep the catalytic converter at a high temperature for low emissions, how much cabin heat you desire, is the ac on all factor into the battery charging, engine running equasion.

Using cruise control will be more efficient than not as the system works more seamlessly. ifyou turn off some accessories the battery stays charged longer and is more efficient. in seattle our weather is mild and i open the window or the sunroof and have all fans off and of course no ac at all. this always improves my mpg.
as many have said these benefits show up in city driving more than hiway, also do have the dealer at the next service check the isc learning to see if it is set correctly, there is a tsb here if you do a search and they will know what you are talking about. if you have a battery that is not original, or any work was done where the battery was disconnected this system may be out of adjustment.

Ahhh... that answers a lot of my questions. Thanks for the reply!

My experience with the car does jive that the car is erring on the side of making sure all systems are fully ready to keep luxury up in sacrifice of hybrid optimization
I'll check on the TSB for the ISC learning
As for the accessories, I noted similar behavior when our return trip was at night (so no A/C), windows up, heater off, and even the stereo off, cruise on.

I understand that city better utilizes hybrid technology

I wish there was a "advanced user" hybrid selection control deep in the menu screen or something that would allow me to say "no matter what I do, go aggressive on electric use", and if that means I get a warning bell saying "I can't give you A/C", etc.

when you are able find a flat road that goes for a few miles in light traffic after the 400h is warmed up and see if you can go only electric up to 20, 25 mph almost 30, but no engine, you will find that after just five or ten minutes the battery is at the two bar or recharge level, so the reality is our systems are not able to go far or fast on electric only, now figure in freeway speeds, the reserve in the battery the way it is configured is not there. that is why at higher speeds electric only is not possible for any reasonable length of time (downhill excepted of course). it will take lithium ion battery packs, or another kind of breakthru to travel electric only for the periods you would like to. some owners have wished for a dial that would reduce power output but allow for more battery use in certain situations and i think that is here in the 2010 model to some degree, where it can be put in an eco mode for longer battery only use, i dont think this is possible yet at freeway speeds.

bottom line you still own a vehicle with an incredibly smooth cvt transmission, that has one third lower emissions than a regular suv, a meaningful reserve of power that is fun to drive, (i think) safe,RELIABLE and comfortable. yes there are compromises however i dont think you will regret your decision, and if you care to it can bring a new hybrid approach to driving.

Really? I like CVTs for their smoothness (no more hurky jerky toyota automatic shifting program which drove me NUTS on the RX330 we had previously) but I find the CVT to be noisier than the standard auto trans which contributes to "audible roughness" instead of "seat of pants roughness".

I'm not hating the RX400h at all, I'm just unfamiliar with a "luxury hybrid".

You can ask the dealer to check the ISC behaviour, or it's easy enough to reset it yourself. I've done it and someone else on here recently did it. Do a search of this forum for the instructions. In both cases (mine and the other forum member) our indicated mileage increased noticeably (in my case about 10l/100km to 8l/100km.

In regards to your highway experience, I've noticed on my 400h that highway driving will hold the batteries at the 80% mark (top of the blue bars, no green bars). Once the battery shows the full blue bars, I notice the flow of power alternates from charging the battery to assisting the engine (or transmission or whatever it assists). The flow of power moves from one to other quite often.

If I'm easy on the gas pedal, I can get to around 60km/h on electric alone. If you can't do this, I'd think the ISC needs to be reset.

What did all that mean in English? I am really curious about what the deaer can do to increase the efficiency of the hybrid system. If they could do this, why don't they do it to begin with? There must be a catch to all of this...hmmm.....I'm so confused....No surprise. Rey

What did all what mean in English? This ISC reset? It's easy to do yourself. Do a search of this forum - I've posted instructions somewhere. Doesn't have so much to do with increasing the efficiency of the hybrid system, but more to do with decreasing the amount of time the gas engine runs (something to do with the idle speed blah blah blah). All I know is that I did it myself, and my mileage and the amount of time I could run on electric only increased.

Very cool, thanks! I want to look into it. What a great forum. I appreciate it. Rey