I've had my 2024 NX350h for 2 years and 1 week and it has consistently displayed the Average Fuel Economy as 33.9 or 34 mpg with my best trip averages around 40 mpg. Today it is displaying as 39.0 mpg and my last trip average shows 70.3 mpg. These numbers seem completely unrealistic. Also, yesterday the gauge on the right side of the display disappeared for a while but came back when the car was turned off and restarted.

Does anyone have any thoughts on what might be causing such a huge change?

 

How often do you reset your average? If you go long times without a history reset the results of an individual trip result will have quite a bit lower effect on the historical average.

Re: the gauge. If only 1 part of the dash screen became inoperative while other parts of the dash within the same screen remain functional, and came back after restart of car, this usually indicates a small glitch in the active memory. Sometimes this could be a software bug or even a minor glitch on the memory hardware itself. Hopefully it was a rare condition for you, technically even a high energy particle from the sun managing to penetrate the Earth's magnetosphere could knock a bit out of place in the car's computer. Not common, but not impossible, LOL. High end data center servers very often use bit error correcting memory to avoid such things, but consumer devices not as often.

But in any case, something to keep an eye on.

 

On the 350H (or most likely all NX's) you will experience a high mpg for a 'trip' if you start the car and maybe move it out of your garage or start the car to move it to another parking spot, or turn it on and sit and wait, if when you started it the ICE came on and consumed fuel. The calculation obviously is way off of reality but I've had these high mileage 'trips' occur too. Just think about it you travelled 20 feet say but you consumed a relatively considerable volume of fuel to travel that far, that's what the computer is doing to calculate your gas mileage for distance travelled. As Droid13 states go into your trips screen and delete all the history and start fresh, it should adjust then after it gathers some more accurate info from a trip. I clear my history out every so often so that I get a more recent snapshot of my mileage and don't include some out of whack anomaly.

 

That definitely makes sense. This trip was 13 minutes over 4.0 miles as I was driving home from the store. Usually, this trip registers as about 40 or so mpg.

Thanks!

 

in my 2022 350h,I have driven 4 miles and gotten well over 65 miles per gallon since most of the trip was in EV mode.

I got 89 MPG the other day, driving a little under 2 miles.

 

4 mile trip mpg is rather meaningless. It can be anything depending if you started from cold or warm engine, full or empty traction battery.

 

Expected. You reset you mpg and drove 2 miles on 88% EV. Actually you can get 99.9 mpg if you try , but that short term mpg is basically meaningless. SORRY

YMMV,
MidCow3

 

Like the old sayings, garbage in garbage out, if it's too good to be true it probably is (except a gas mileage calculator is too simple to realize it!).

 

I had exactly the same situation. My average mpg was 36.8-37.2 for about 18 months and then suddenly, while I was driving! started to increase to 39.something. Now it is somewhere around 40-40.2 mpg. Total BS from my perspective. It is definitely a bug in Lexus software. Also, IMHO, the car should maintain the total average mpg from begining of times, and you are not supposed to reset mpg. A driver can reset mpg for a trip, but not for a whole thing.

 

I'll bet if you can dig into the data stored in the ECM through the OBD port and use proper software you can see these details. I've watched videos where they see total miles driven etc. What were getting to play with is just a simple pocket calculator nothing special.

 

That is certainly the driver's choice. I reset mine at the beginning of each calendar season so my next one is due in a couple weeks when fall officially arrives. The fuel efficiency of a vehicle varies quite a bit season to season so that way I'm always comparing apples to apples instead of wondering why my MPG is dropping when its -20 outside. The history screen retains I think around 6 previous sets of data so I can see seasonal trends. I'm currently tracking at 8.4L/100km (~28mpg) since the start of summer which I think is pretty decent considering turbo non-H and 66% city driving and I drive like I like it. But I know it'll start to decrease probably as we get into November.

 

Since my wife and I are self employed and use our car for work occasionally, I take advantage of the tax break on vehicle expenses used for employment we have here in Canada. I put all gasoline purchases into an excel sheet listing date, trip distance and total kms to date, cost of fuel, cost of fuel per litre or gallon if travelling in US, amount of fuel taxes. Plus I note all purchases for the car including service work, tire swaps from snows to summers, supplies like windshield washer fluid, wax, cleaning products etc.

From this data I can pull out gas mileage for whatever date interval I want. But by and large I don't pussyfoot my driving at all, I get between 6.0 (39.2 US MPG) to 7.2 (32.6) litres per 100 kms and winter it may get up to 8 (29.4) litres per 100 kms. I don't sweat the tiny details with this data, it's pretty darn good compared to V6 mileage I was getting before which was 12-15 L/100kms (19.6-15.7). Of note I've never put anything but regular fuel in the car plus I always use Top Tier or good brand name fuel only, and no additives.