Actual Mpg Vs. Displayed Range Fluctuates Widely

[jebrx 350]

I'm a first time Lexus owner and happy with no regrets. I did however pay a trusted automotive shop to check out several used 2009 RX350 vehicles with 36 +/- K miles that enabled me to request a new brake job and switch a brand new set of tires for our preferred brand and 1 (one) item covered under warranty. Because I researched Consumer Reports and had decided on the RX350 my shopping was fairly easy using my paid adviser. The salesman/dealer willing to deal and not say my adviser was wrong on the brake job and switching tire brands got the sale.

My questions is: regarding actual...current fuel consumption the display indicates a wide range; fluctuates from the teens to the 90s and this is something that I just noticed this year and have 53,236 miles. I have watched these INFO numbers during my 16,736 miles and have never noticed this until this year. I realize the only way to get actual MPG is to fill up my tank and write down the mileage and then repeat w/fill up and do the numbers. I know...think that the current numbers running is only an estimate but to 90, 50, etc.; could a fuse be blown? I appreciate any info that I can use before addressing this to a tech/mechanic at the dealer. Thank you, Jeb

[RX400h]

According to my 2009 Consumer Reports buying guide, the vehicle that sat at the top of the luxury SUV list (with a score of 83) is the RX400h. The RX350 is next on the list with a score of 80. The 1-2 ratings of these vehicles repeats, year after year, although in 2013, the Acura MDX was placed ahead of the RX350, but below the RX450h, which continues to dominate this category, today.

But getting back to your question:

We have two vehicles with built-in "instantaneous MPG" readout capability and another with a Scan Gauge II connected to the OBD II port. All three vehicles will show wildly fluctuating instantaneous MPG readouts, so I think it's a fairly useless "capability". You are far better off displaying the average MPG readout, but keep in mind that this is not always perfectly accurate. As you mentioned, calculating gas mileage, manually is typically the best way to know what you are getting.

[jebrx 350]

Thank you Dave for responding, now I can stop worrying. I do wish I had the integrated back-up camera and intuitive parking assist features. Do I dare trade in for a newer model with these options? I've not researched Consumer Reports for their results so I don't know if it would be worth the additional cost. If you have an opinion, I'm open for suggestions. Thanks again, Jeb