I've got a new RX 400h 4wd with 1,800 miles on it, and I'm so very disappointed in the mpg.

My last tank took me through a couple of weeks of Minnesota sub-zero temps, (two mornings as low as -10º), mostly driving short city trips which I know are the worst, but I wonder, does anyone think 15.01 mpg is within acceptable range given the conditions?

I drive for conservation, I have a heated garage, (58º so the car always has a warm start), and I've only run the defrost twice for 5 minutes, I often run the heater at low fan speed, and I know the winter gas blends are less efficient, but still. The dealership checked it out today and found all systems running normally.

Before we hit sub-zero for 9 days straight we were generally between 0 and single digits. The best I could get with those temp conditions was 17.89mpg and 18.4mpg for the previous two tanks. Pretty disappointing. The one highway trip I took was in early January when temps were unusually warm here at 20ish. Cruise control all the way at 65-75 mph got me almost 26mpg. That was my first tank and I was thrilled that an SUV could do that well. But this last tank really hurt.

These numbers are actual mileage per gallon calculations, not the "average mpg" nav. display which is generally an inaccurate 5 miles or so higher.

The car drives like a dream, it's comfortable, well appointed and excellent in the snow and ice. This kind of mileage is ok for a vehicle of this weight, but it's a difficult pill to swallow when the sticker says 31city/27hwy. While I know the mileage sticker is wildly optimistic, I had hoped for better than a mere 50% of it's estimate. All the posts I've seen here seem to average low to mid 20's which I would be thrilled with. Is 15.01 just going to be my reality in deep cold Minnesota winters?

Anyone doing better at similar low winter temps? I see even the super mileage Prius folks are taking a winter hit, but 15mpg for a hybrid, (oh excuse me, a "performance" focused hybrid)? Sounds like a contradiction in terms. At least it's got cleaner emissions.

C.

 

Sub zero temps are going to kill your mileage in anything. 15-18mpg for that car sounds about right to me, because it is essentially running without most of the hybrid functionality while the gas engine struggles to get itself up to temp. Things will pick up with the warmer weather.

 

I agree that low temperatures - especially single digits and sub zero temps- cause most of the fuel-saving programming to go into hibernation.

The engine will run continuously and often at 1500 RPMs when idling instead of 900 RPMs even when stopped - even after the engine has seemingly reached operating temperature. the engine coolant will hover around 170- 175 degrees F and never seem to get to 181 degrees. Only a long drive (typically greater than 45 minutes) in sub-zero temperatures seems to reactivate the engine shut-off feature.

The regenerative braking is reduced and the friction braking is blended-in in greater proportion. Note that the power gauge needle will not dip even half way into the blue range with substantial braking unlike warmer temps where the needle can easily peg the bottom of the blue range with moderate braking.

I use an engine block heater so my engine coolant temperature starts at approximately 90-100 degrees F each morning. Coming home at night from the office, I suffer thru a cold start. I typically have a 9 mile, 20 minute drive in the morning and again at night .

From January 27 to February 14, I averaged 22.4 miles per gallon. The average daily temperature over this period was 10.7 degrees F.

Last August with average daily temperatures of 76.5 degrees, I averaged 29.3 MPG over the same route and distance.

 

The worst I ever got was around 19 with my HH. (I record all my tanks in the mileage database and all are actual readings) You may be seeing your lower numbers for a number of reasons 1) there was a TSB that came out on setting the Synergy drive at the dealer prior to delivery, some dealers didn't perform it and low mileage was a result (it was either on this forum or the Tundra Solutions one for Highlanders); 2) low mileage and the cold. I too was disappointed with my mileage when I first got my HH, but like others pointed out it really needs about 5-10K miles to seat in and show it's stuff. In the warm months I now get over 30 MPG in town and a steady 26+ on trips, however in the winter 20-24MPG is the best I see and usually around 20 MPG in the cold weather and my short trips.

I believe your -10+ degree weather, short trips and less then 5-10K miles are all contributing to your lower mileage readings.

 

Bob259,
Sorry, I'm new here and just beginning to learn how to get around on the forms. I'm embarrassed to say I don't know what a TSB is. A directive of some kind? I've searched on this form and also looked for Tundra Solutions, but no luck. I'd like to call my dealer and confirm they've done what they need to, but I'd like to to be more informed first. Can you help a newbie out and point me in the right direction? Thanks.
C.

 

No problem....

TSB = Technical Service Bulletin

Tundara Solutions is another forum site http://www.tundrasolutions.com/forums/index.php

 

Sub-zero??? Brrrrrr!

I have forgotten to record my last few tanks (until today) but your #'s sound pretty similar to mine. Now that it has warmed up in SE Michigan (30's during the day) my gas mileage is "up" to around 19mpg.

I have to believe what Don mentioned is correct. Normally, without any heating demand, my engine shuts down at every red light and during coasts. Now, with the heat on full time, it rarely goes off. All that extra idling must use fuel, so it will be reflected in the mpg. Basically we lose the efficiency of the hybrid design once things drop below freezing. 18-19mpg (for me) is a vast improvement over the 12-13mpg I used to see in my VW Touareg, so I won't complain too much!

 

You may want to consider using 0W-20 motor oil - especially in the winter.

Here is the Toyota TSB which has additional info.
http://www.chrysanindustries.com/pdf..._tsb071002.pdf

If you go to your Toyota/Lexus dealership, you have to specifically request it.
Otherwise you may get what's in their bulk tank which is most likely 5W-20 or 5W-30.

 

Since your 4WD RX400h remains primarily FWD it is extremely likely, as a safety issue, the coastdown "form" of regenerative braking is completely disabled when the OAT is sub-zero, highly likely even below freezing.

Additionally, also as a safety matter, the FEH/MMH SUVs disable regenerative braking the instant ABS activates during actual braking, so might your RX.

Then there is also the issue of keeping you, and the catalyst, in a satisfactory operating zone.

 

Sorry, I should have mentioned that Ford has a patent involving the FEH/MMH hybrid drive system wherein the regenerative braking system's capability is substantionally reduced as the OAT declines to, and below, freezing climates. It is very likely Toyota uses the same technique.

Additionally I would not be at all surprised if upon ABS/VSC or TC activation there might be a follow-on period of time that, as a matter of safety, the regenerative braking energy recovery system is completely disabled, just as it is during one of these "events".