Last post on Mar 24, 2013 at 12:44 AM
You are in the Lexus RX 400h
What is this discussion about?
Lexus RX 400h, Lexus, Hybrid Cars
#1897 of 2363 Re: 2006 Lexus RX 400h: The Hybrid Emperor's New Clothes [c2rosa]
Aug 04, 2005 (1:00 pm)
As a prospective RX 400h buyer, I was also upset by the NY Times articles. However, after reading virtually every posting on this forum (it's been a long afternoon!), I realized that the reviewers may have been testing new cars not yet broken in. Most of the early posts indicated that the gas mileage went from disappointing to as good as, or better than, the EPA ratings once the cars had over 1000 miles on them. I am much more encouraged by what I'm reading currently. One other thing I don't remember being mentioned is cruising range. Our 1999 RX300 averages about 300 miles per fill-up. It sounds like the 400h extends that by about 100 miles (same small size tank: 17.2 gallons) 25 MPG. That will be very welcome.
Aug 04, 2005 (4:58 pm)
As we were just about to buy the H, and instead got the 5 bmw stationwagon, I thought you all may be interested in an observation...Drove the car on a short trip of about then miles and checked the milage for gas consumtion...I drove regularly and got seventeen. mpg. and I would think, had I gotten the h it would have been twenty five mpg....Just goes to show that short trips really do use the fuel much more than a person would think....As a percent the h gets a lot more mpg..Tony
#1900 of 2363 RE: NY Times artcile
Aug 04, 2005 (8:18 pm)
I recently drove a similar route through Michigan (in a Matrix, 32+ mpg!). MI has a 70 mph speed limit on most highways and most people drive 80-85. Add in the fact that it has been very hot and AC was probably running full blast and I think that explains the problems. The ratings are usually for 55 mph with no AC running. I have read that the mpg drops after sharply above 65 mph.
#1901 of 2363 Re: What do I think.....??? [wwest]
Aug 05, 2005 (11:14 am)
I remain a bit puzzled about why owners are reporting better MPG on highway, ~28, versus city, ~24. Everything I know would indicate better city MPG as in our 2003 Prius.
I've been meaning to reply to this part of your post though it has taken a while to get around to it. We now have more than 3000 miles on our RX400H - about 85% city/suburban and 15% freeway. What I find is that city driving is much more variable than highway driving in a number of ways. For instance, some people's city driving is on short trips. The first 5 to 10 minutes of driving have the engine operating less efficiently. I find that when I do short trips (under 5 miles of city driving) I get around 21-24 mpg. When I do driving similar to the EPA profile for "city" driving - a stop about every half mile, cruising at around 25 to 40 mph between stops, spring weather so no or mild AC - I get around the EPA number. Really bad stop and go with lots of AC can lower that substantially.
Also, analysis shows that the mileage during lower speed driving is more heavily influenced by other factors such as AC load. In message 1753 I showed in calculation that the same AC load that drops freeway mileage from 27 mpg to 25 mpg could move city mileage from 31 mpg to 24 mpg. That was for city travel at an average speed of 20 mph like the EPA profile. In really bad stop and go, it would be an even bigger hit.
Therefore, it isn't surprising that the city mileage is more difficult to predict than freeway mileage. It can easily be better than freeway mileage for some conditions and worse for others. Your Prius may be saved from some of the short trip penalty by its coolant thermos and in the Pacific Northwest you may not get as heavy AC load as we get on a regular basis. Temp was already above 80 degrees F when I got to work this morning.
#1902 of 2363 Supposedly....
Aug 05, 2005 (2:36 pm)
the biggest "gain" from the Toyota Hybrid concept is the regenerative braking aspect, recovery of coastdown and/or braking energy, that would otherwise be disippated into the atmosphere as heat.
So city stop and go traffic should result in stellar gas mileage over an equivalent non-hybrid vehicle just as the EPA estimates indicate.
Yet the reports here seem to indicate highway mileage substantially better than city.
Is it because the catalytic converter must be kept FIRED OFF...??
On the highway the ICE must run continuously anyway. Must it often run in the city because the thermocouple in the catalytic converter indicates it needs to be reheated?
And does the A/C rely on the reheat/remix cycle like all other Lexus automatic climate control systems? In which case the engine coolant would also need to be kept continously HOT.
I noticed that in the 04 and later Prius a c-best option was added such that the A/C reheat/remix cycle was disabled so there was no need for the ICE to run ONLY to keep the coolant HOT.
Maybe Lexus thinks that would be too discomforting for a Lexus owner.
#1903 of 2363 Re: Supposedly.... [wwest]
Aug 05, 2005 (4:06 pm)
wwest, I think the issue is that the biggest gain of the hybrid over gas only is different from the best mileage. For example at freeway speed under certain conditions perhaps the hybrid would get 27 mpg and the conventional would get 24 mpg. One would be saving .0046 gallons per mile. If in city driving one gets 24 mpg with the hybrid and 21 mpg with the conventional (the same 3 mpg improvement) one would be saving .0059 gallons per mile or 28 percent more gain per mile even though the mpg number doesn't look as impressive. The RX330 city EPA number is 19 mpg and presumably it does worse than that under the same variations that move the RX400H city mileage from the EPA rating down to 24 mpg (short trips, high AC, etc). At 19 mpg city for an RX330 versus 24 mpg city for an RX400H, one would save .011 gallons per mile with the RX400H - a much better gas savings than on the freeway.
I expect that if one drove the hybrid RX400H in heavy stop and go versus the RX330 in heavy stop and go one without AC running one would see a very satisfying difference in the MPG numbers. If the same is done in weather with a heavy AC load, one should still see the advantage in MPG numbers and if you calculate the improvement in volume of gas used per a mile it should be about the same difference. The mpg numbers however will look closer together because of the AC load added onto the movement load. (See Dylan Hixon's post at 1878 for an explanation of why.)
I've answered some of your other questions before but I will try again:
When running in city driving, I still only see the ICE come on when I'm actually demanding power that justifies it or when the battery is getting low. The only exception I see to this is right after turn on when the engine is cold. For the initial warm up (first couple of minutes of driving) the engine may come on for any gas pedal pressure even if there is power in the battery and one is only accelerating slightly. Other than that, I don't see the engine cycle on for keeping the catalytic converter hot.
Yesterday, when there was an accident on the freeway that had me in very slow traffic (stop then go forward at a few MPH then stop again) for 15 minutes, I didn't see the engine come on until the AC had run the battery down to two bars.
I don't think it relies heavily on reheat/remix cycle. The AC load, in terms of hit on mileage, seems to be proportional to how hot it is outside. If it was relying on reheat/remix (run the AC at full cooling whenever cooling is needed then use the heat from the engine to warm the air to the desired temperature) then I would expect the AC power drain to be high even when it was only having to cool slightly. I don't see that. Possibly in the RX400H they applied what they learned from the Prius and have it default to not doing the reheat/remix.
I think the catalytic converter heating and the coolant availability for heating (when the weather requires it at least) are contributors to the lower mpg experienced during the first few minutes of driving but not to the steady state conditions.
By the way, around here on the freeway I don't see the ICE on continuously. The freeway is not flat. Cruising on the freeway as I go up and down the little hills I see all the states - ICE only, ICE splitting its power between the wheels and the battery, ICE plus electric to keep up speed on a modest upgrade, electric only on a mild downgrade, regeneration on a steeper downgrade. We often have free flowing but heavish traffic so it goes through the same states as I adjust speed to variations in the traffic flow. It isn't only when the ICE goes entirely off that the hybrid saves gas. When the motors draw energy to supplement the engine so that it can stay at a more efficient operating point or when the conditions don't require all the power from the ICE to go to the wheels and the excess is saved in the battery again keeping the engine at a more efficient operating point, it also improves mileage.
Aug 05, 2005 (7:17 pm)
of and in itself cannot be easily modulated. Older systems had no refrigerant reservoir and used a capillary tube mounted near/against the evaporator face with a variable spring load against the capillary pressure to operate a switch which in turn controlld the compressor clutch. Adjusting the spring pressure via a knob controlled have often the compressor would run and thereby the "average" evaporator temperature.
Almost all modern day system have reservoir and the compressor run when the high side refrigerant pressure drops to the low limit, the reservoir is empty. To prevent freeze up the old capillary system simply controls the expansion valve. IF the evaporator surface starts to decline below freezing the expansion valve closes.
So, the evaporator always operates at about 33F when the A/C is on.
The 2nd gen Prius uses the blower speed to regulate your comfort level when the rehea/remix is disabled via c-best option.
You might try extending you fuel economy the same way I do in most of my vehicles. Turn the system to max cooling and then use the blower speed to regulate your comfort level. Max cooling bypasses the reheat/remix cycle and thereby the A/C will operate much more efficiently.
A few years ago coming across AR with the temperatures in the 100's my engine started overheating. I discovered that one of the radiator/condensor cooling fans had failed and so we drove most of the way across AR with no A/C. Then I realized that if I used A/C on max cooling that would substantially increase A/C efficiency and reduce the load on the condensors and thereby the radiators. Drove all the way home to Seattle that way.
#1905 of 2363 MPG-reported here-25 mpg average-
Aug 06, 2005 (3:57 pm)
I should stay out of this,since I'm aiming for a HH,(prices are dropping-Carmax has one for <$32000,and locally-NewOrleans for $33300 and our dealers are predators),but I don't have any sense,so here it is. These are the figures-and a couple of comments) reported on your MPG thread-25,22.7,28.8,26,19.4(worst,but he does a 1.5 mile commute),29,27,25,22,28.2,24,24.5,29,26,27,25,26.5,23(in Phoenix and using the AC constantly),25(all hy he says his RX330 would do 22 on same route),27,27.06,25.04,28.19,26.25,25.98,27.1,28.41,(these last 6 figures are the "best"-the member gave calculated and nav screen mpg figures over a 1954 mile trip with notes on roads,altitude,AC etc-his trip total was 26.98 calculated and 27.66 by nav screen.He also mentioned that this was about 4-5 mpg better than his RX330 would have delivered-it was hilly,so this wasn't just a straight flat no regen braking hy trip.These are the best numbers here-and they are "good" in all respects) 22(city heavy AC use),24(city),20(very unhappy,no help from Lexus USA-thinks vehicle is essentially" broken" in some way,but Lex says no.I think he has a point-this is 5 mpg less than the rest of you), Well,that is it.I averaged the 1st 10-it was 25 mpg.Someone else can do a complete average.I am fairly certain that these are NAV numbers not calculated numbers.Thanks to your meticulous member,you could just drop it 1 mpg-his calculated was 1 mpg less than NAV(it might be just his NAV is "off" 1 mpg,but who knows-unlikely to be much more than 1 mpg in any case-HH members have gotten calc and NAV numbers very close-couple of 1/10th) Worse case,you guys get 24 MPG actual calculated-this is very good by any measure.My Pilot gets 12-13 city and 22 hy(at 74 mph AC blasting in summer).The Pilot,Highlander,and RX330 are actually the best Midsized SUV's in respect to MPG-check CR.Your RX400 will "beat" them like a drum in city mpg.Pure interstate travel will be close mpg wise-no reason it wouldn't be. When CR comes out with it's report,will have excellent comparative numbers. My guess is RX400 18-26(CITY HY) the RX330 AWD gets 12-26(CITY HY) in this same test.CR has a very harsh city cycle.The NYT reported didn't lie,but he did essentially a HY trip,so no reason the MPG would be much different. He did us-late buyers-a favor of course.It forced dealers to D/C the $5000 gouge!!Just pull out that article and bargain!!They are actually at and below MSRP!!Heck,we should all subscribe,and send him flowers! Luck,Charlie PS The numbers over at HH are about 1-2 mpg better-just what you would expect.
#1906 of 2363 Re: MPG-reported here-25 mpg average- [phoebeisis]
Aug 06, 2005 (7:18 pm)
phoebeisis...Are you seeing significant discounts on the 400h in your area?? How much?? I know that the dealer in Shreveport offered $1500-$2000 off in June but he told me after June 30 there would be no discount. In CA, people are still on waiting lists for the vehicle. Wonder what deals will be offered during the Lexus December to Remember Sales Event??
Personally, I think the 400h is nice and it has a lot of power. However, for the price, I think it should have genuine wood trim, satellite radio and better instrumentation. Just my opinion. I understand that satellite radio will be offered in 2006. Perhaps a discounted 2005 RX330 (if available) would be a better deal.
Before purchasing a 400h, my brother considered the HH but he didn't care for the styling and the new, more modern body style is a year away.