drpepper

With all of the mileage talk, some completely dependent on the display mpg, I had been curious to test my display vs actual mileage.

I did a 400 mile trip yesterday. Probably 95% highway, doing 70-75 mph often and 80-85 any time someone leading me was doing that or better (I forgot to check the average speed the computer registered). My total time on the road was right around 6 hours, including one stop on the way there and 2 on the way back, so the mean would have been between 65 and 70.

The computer had the mpg at 26.3 and the actual was 26.6. Again, no earth shattering information there, but the computer did better than I had suspected it would. And I really thought it was going to err to the high side, so that was a surprise too.

ecount00

that's a very good result especially for the speeds you mention. agree, surprised the computer was that close. even if not, for me when it's within +- 1.5 mpg, that's close enough for my purposes.

drpepper

Yeah, that's what I was thinking.

I've intended to check my local driving mileage a few times, but I keep forgetting to take down the numbers when I fill up. I'm still going to try to do that. For my normal day-to-day driving the display tank avg usually settles in right around 19. I know that the display can get skewed, but now I'm even more curious.

drpepper

Well I have a tank of local driving that I managed to keep the numbers for, and I'm surprised by the accuracy of the display again.

I've had mostly normal daily commuting/around town driving over the past 10 days and one ~70 mile round trip down and back on I-95.

294.6 miles on 14.9 gallons is 19.8 MPG and the car's display said 19.7 MPG.

The display clearly can be tricked by certain types of driving, but my suspicions about it being wrong for typical driving, especially averaged over a tank, was just wrong.

vrferrari

I've always found my 99 GS4's NAV mileage information to be fairly accurate, even when taking into account my 20" tire upgrade.
The best thing I've come to appreciate about the NAV screen is the "instant" mpg readings, which I have used to great effect to change my driving habits and better my fuel economy per tank averages up 2+ mpg. That equates to an additional 32-50 miles per tank (usually 16 gallon fill ups). At a 75 mph cruise with 95% hwy useage I've registered and calculated almost 30 mpg out of several tanks of fuel.
Your car should be even better !

whlkev

here is something i did

https://www.clublexus.com/forums/sho...d.php?t=373438

vrferrari

Yeah, I remember seeing that post.
Up to last week I was running on my factory 235-45-17 tires while I was awaiting my replacement 275-30-20 rubber. While running on my stock tire/wheel combo for several weeks I saw a significant jump in my overall fuel economy versus my 20" combo.
I challenged myself to maximize my range on a single tank of fuel and with my 70% hwy 30% city driving , drove her down to the "Low Fuel" reading on my NAV screen......397 miles on 16.3 gallons = 24.3 mpg.
Did not want to push it too far but it looks like I would have had another 2 gallons of fuel onboard.

drpepper

I hear ya, but just for me, I'm not going to work at using techniques while I drive to "artificially" increase the mileage that the car would otherwise get. Part of driving and choice of the car I drive is for enjoyment. Again, while I understand doing it, for me, it would take away from enjoyment of the car.

The mileage I'm getting would seem to line up well with what's reasonable and reflects that my engine is running well and my tires are properly inflated

That said, for you to get nearly 30 MPG out of a V8 is impressive

vrferrari

I understand what you're saying. The key factors for me were to change my original driving habits that gave me no positive results in return:

1) anticipating lights : I now pay more attention to observing the traffic lights so as to keep my forward momentum going. All cars waste a considerable amount of gas accelerating from a stop, so if you can minimize these types of situations you could see significant gains. Even a slow rolling start is better than a dead stop. Every time you use your brakes to decelerate you "waste" the energy (fuel) expended to get yourself rolling in the first place. This is the key area that all Hybrid cars gain their most mpg gains; engine shutdown at the lights and battery assisted take-offs from a dead start to minimize the running time of the gasoline engine.

2) Minimize "jack rabbit" like starts : realizing I don't need to use my advertised 0-60 max performance runs at every light. It's interesting to note that excessive "very light throttle" acceleration starts that dragged out my time to cruise speed also waste gas.

3) Cruise control !!!!! I use it everywhere, even in town. I've found that the GS cars like to run and I've found that if I don't use the cruise to keep my target speed in check I'm creeping up to 10+ over the speed limit and have to use braking to slow her down. Any time you are using any throttle input your instant mpg meter will drop (sometimes significantly). Getting to my target speed and punching the cruise control has minimized this yo-yo affect of accelerating then having to deccelerate. I also note that the Lexus cruise control is better at holding throttle postion than I am.

4) Limiting my hwy cruise speed to 75 or below : one of the toughest parts for me, especially in rush hour traffic in Phoenix. Keeping my speeds at or below this gives me a cruising rpm of less than 2400 rpm (20" tires") and minimizes my aero drag. On cruise at 75 (indicated) on level ground I see my instant mpg hover around the 30 mpg mark, which appears to be very close to my computed consumption when doing my refills.

Doing these 4 things has really helped my fuel range without me really sacrificing my enjoyment factor; it really showed me how "wasteful" my original driving habits were.

Plus, these savings tips put mileage back into my tank to offset my occasional max performance 0-60, 100 mph cruise and smokey burnouts sessions.

Great cars I'm telling ya....