That’s great mileage! Why are our readings so completely different? I’m at about 1500-1800 ft above sea level & relatively flat. Local speed limits are 65 & below. US Highways are 70-75 & I-10 is 75-80mph. I don’t drive on I-10 very much.

 

Flat terrain and highway speeds are actually not good for hybrid mileage. On a flat road, you cannot take advantage of coasting downhill to regen the batteries. You'll just end up having the ICE come on more often to recharge the batteries, especially if you use EV mode too much. And of course at highway speeds, the brakes aren't used much, so there's even less regen happening.

Note that DocRock mentions a lot of hilly terrain at 25-35 mph speeds. Those are near perfect environments to get great mileage with the hybrids - coast downhill to regen while potentially braking and keep the batteries fully charged; and then on the uphill parts, there would be enough juice in the batteries to keep the electric motors going most of the time. Repeat the cycle when you crest the hill. You could go miles in those conditions without the engine kicking in at all.

 

I agree with your statement. It’s the only logical explanation that fits. I have certainly learned my lesson on hybrids with this car. Given that, its doubtful I would buy another RX again. It doesn’t tow well, it doesn’t provide me with the advertised mpg & it has been plagued with stupid little things that Lexus was supposed to have been free of. As mentioned earlier, if the LS could tow, my RX would be gone. It’s sad that my 6.2 V-8 Camaro SS, gets better mpg than this Lexus hybrid. I would still recommend the RX to others, but with caution in its use.

 

I'm not an automotive engineer or a physicist, but here's what have noticed about the operation of the ICE and hybrid (traction) motors in the 450h. When the ICE is operating, it is feeding power to the front wheels and charging the hybrid battery (unless it is fully charged). The electric motors help power the car even when the ICE is operating so long as there is a sufficient charge in the hybrid battery. So, even at highway speeds, the electric motors are taking some of the load off the ICE. For example, on a downhill grade, I have found the ICE sometimes shuts down completely as the traction motors can easily handle the load. The "ECO" light doesn't come on at speeds above 40 MPH, but that doesn't mean the ICE is engaged.

Ironically, I believe the 450h gets better mileage on hilly terrain than on flat terrain. Here's an example: the climb to the summit of Cadillac Mountain at Acadia is about 1,000 feet over 3.5 miles. Obviously, the ICE is operating practically all the time. However, on the descent, the grade is sufficient for the ICE to completely shut down over the entire 3.5 miles while, simultaneously, regenerative braking is charging the hybrid battery. On our two trips up Cadillac, we followed the descent with a drive along the Park Loop Road (beautiful drive, BTW). The speed limit is 25 MPH and the road has some slightly hilly sections. Both times, with a fully-charged hybrid battery, I was able to drive more than 5 miles on the Park Loop Road with the ICE hardly ever engaging. And, my indicated MPG at that point was higher than before we started up Cadillac Mountain.

Practically our entire trip was on hilly terrain (the Appalachians were "with us" most of the time). But, the hits to MPG we took when going up a hill were more than compensated for by the electric motors carrying the load going downhill.

 

2020 RX450h fill up at 2,655 miles 8/12/21. Traveled 393 miles, all city, short trips mostly 14 miles each way, warm weather mostly a bit above 90 degrees F.
30.1 mpg calculated. The RX said 30.5 mpg. Filled up with QuikTrip Premium.

 

2020 RX450h fill up at 3,074 miles 9/25/21. Traveled 419.1 miles, all city, short trips mostly 14 miles each way, warm weather mostly a bit above 80 degrees F.
29.8 mpg calculated. The RX said 31.4 mpg. Filled up with QuikTrip Premium.

 

2020 RX450h fill up at 3,512 miles 11/12/21. Traveled 438 miles, all city, short trips mostly 14 miles each way, cooler weather mostly a bit above 70 degrees F.
30.2 mpg calculated. The RX said 29.4 mpg. The Lexus dealer filled it as a [size=13px]curtesy[/size].

 

I expect my mileage to drop off about 3-5 MPG during the winter months. The heater and defrosters (windshield, liftgate and mirrors), the steering wheel heater and the "bun warmers" all draw electric current. It takes the ICE longer to reach operating temperature. Fortunately, the traction battery is inside the car instead of being exposed to the outside temp once the cabin warms up.

I discovered with my previous hybrid that the bun warmers and steering wheel heater often kept me warm enough to minimize the use of the heater. Not the defrosters, though.

 

Winter gas is the killer for me. Our winters are mild by comparison to other areas, but the shift to winter gas drops a solid 2 MPG. I can tell immediately when they switch.

 

Exactly. This is pretty clear on the window sticker of City vs Highway mileage (31/28) that you need to be in regen conditions for optimum mileage. This is exactly why I bought a hybrid, because my commute mimics those conditions very well, and I now am getting 5 mpg better than a 4 cyl. Rav 4 with near twice the power and comfort. This is also why it's silly to argue about another persons mileage. Conditions matter in a big way and that would include average temperature also.

 

NOTE: This is the experience with my wife's 2020 RX 350. Not my 2021 RX 450h. I thought I had posted this in the RX 350 Mileage page. Sorry about the confusion.

We returned from Virginia on Thanksgiving Eve. It's a 220 mile trip of which about 90% is interstate (or otherwise limited-access) highways. Sunny, no wind to speak of. Mid 30s temps when we left; 40s most of the time. Typically about a 4-hour drive. Tank was full with winter gas.

Unfortunately, there were several stop-and-go traffic delays along the route (ironically, the DC Beltway flowed smoothly). That turned the trip into a more than 5-hour drive. Traffic backed up approaching Frederick, MD; on I-83 in Harrisburg, PA; several miles before the I-81/I-78 split east of Harrisburg; and, on the-always-annoying US 22 in the Lehigh Valley.

Nevertheless, we averaged 30 MPG. Not complaining.

 

2020 RX450h fill up at 3,934 miles 12/5/21. Traveled 422 miles, 50% city, short trips mostly 14 miles each way, 50% highway 70mph, weather mostly a bit above 50 degrees F.
29.7 mpg calculated. The RX said 29.3 mpg. Filled up with QuikTrip Premium.

 

Refueled just before my 12-month service at my Lexus dealer.

Here are my first-year mileage stats:

Miles driven: 7,103 (I estimate that about 75-80% were highway miles)
Gallons of fuel used (full tank to full tank): 196.25
MPG: 36.19
Average cost of fuel (always Top Tier Premium): $3.38 per gallon
Fuel cost per mile: $0.094

 

2020 RX450h fill up at 4,326 miles 1/23/22. Traveled 391.4 miles, 100% city, short trips mostly 14 miles each way, 0% highway weather mostly cold..
27.3 mpg calculated. The RX said 28.5 mpg. Filled up with QuikTrip Premium.

 

2020 RX450h fill up at 4,651 miles 3/2/22. Traveled 325 miles, 100% city, short trips mostly 14 miles each way, 0% highway weather mostly 50F to 70F.
30.1 mpg calculated. The RX said 29.3 mpg. Filled up with Sam's Club Premium.
__________________
2020 RX450h Luxury Package, Atomic Silver, Black, 20" Michelin.
2013 ES300h UL, Starfire Pearl, Parchment, Michelin, LDA, ML, PCS, BSM, IPA, DRCC, PTO/C - Trade-in for RX450h.
2015 ES350 UL, Atomic Silver, Black, 18" Michelin, LDA, ML, PCS, BSM, IPA, DRCC, PTO/C. - Trade-in for RX450h
Member of the Lexus Advisory Board