barry1955

I have a 2010 RX450 with 5100 miles on it. I have been averaging between 32.5 and 33 miles to the gallon consistently since I got the car. I have a habit of trying to "top off" the tank any time I refill it. I was curious if anyone knows how the car determines MPG and if topping it off might be the reason mine is so good ?

Cruiter

You're correct on the possibility of damaging the carbon filtering system if overfilling. You should just fill till the pump stops (The 1st time) and no further.

However the computers mileage estimates are on miles driven and the gas used based on how much is metered in. The computer can not base it's calculations on gas remaining in the tank as that is just a 'gauge' meaning not accurate but a gauge as in "estimate: judge tentatively or form an estimate of (quantities or time); "I estimate this chicken to weigh three pounds" " (1st line of Websters definition of gauge). A lot has to do with where the 'power' gauge is as you're motoring down the road and the miles driven. It's very similar to a manifold pressure gauge or maybe even the same thing with different nomenclature.

BTW, it's been cold and my reading since 1 Dec on miles driven is down to 28.6 and on the current tank with longer trips it's 30.6
The lower figure is due to cold temps and many short trips less than 4 miles.

RXSF

Topping off is a bad habbit. You arent going to travel that many more miles by topping off a minuscule amount of gas, rounding the price really is a mental thing and doesnt make much sense unless you pay cash, its bad for the environment if you overflow as the gas just evaporates into thing air, and I heard (though not sure if its a rumor) that you dont actually get any more gas and that it goes back into the gas station.

but it wont affect your gas mileage

Cruiter

I guess some things in life will continue as a mystery unless someone with factual knowledge on this chimes in.

Because of a small gas war in my local area, I did top off the other day and had driven less than 75 miles since previous fill up. I noticed immediately on leaving the station that the 'mpg since fill up' remained at what it had been prior to filling up (30.7). Normally it resets to '0' and works back up as you start driving while the 'average' remains as that since last manual reset. That just lends to the mystery

Bonty2011

this is really great... makes me feel like I made the right decision to purhase 2011 RX450H. However, I am getting terrible gas mileage. I live in California and weather is in 40's and 50's but getting 18 MPG. Horrible.... my second tank is even lower. The car is in service for diagnostics. Does anyone ever experienced such a low mileage?

Bonty

wa3cuj

I typically fill up when I get to half a tank and the "mpg since last fill" has always reset itself.

Cruiter

Bonty
Can you describe as accurately as possible you're normal drives everyday re: distance, frequency of stops, speed, etc.?

Also some people have the false notion that simply buying this car in Hybrid form will give them around 30mpg. It can but you also have to adjust your driving habits somewhat. Avoid jack rabbit starts, and hard stops. Try to maintain steady speeds as much as is possible. Plan your trips with economy in mind and be aware that short trips of 5 miles or less will drastically reduce economy in any car.

Now if you live in the hills of S/F than that will defiantly reduce your economy

Let us know what the diagnostics say if you can.

Cruiter

If I try I can exceed that quite a bit. Getting 30 really isn't that hard, it does require trips usually around 10 or more miles and conciseness driving. If you're going 20 miles and drive it right it might take you 5 minutes in mixed driving longer than it used to but you can do it. Slow and easy is the key.

I get that quite often, in fact this past weekend I made a trip down to Milledgeville. It was a mix of rural route, state hwy, and interstate. I was 31 and change round trip. The distance each way was about 145 miles.

I used to never travel without my trusty radar detector. Now I travel the speed limit and leave it at home.

Traveler1

I have heard from Prius driver that the meter won't be reset refilling less than 15 liter (3.4 gal.).

Mkml63

My mileage is not as good as I expected, abt 19-22 with Eco mode on and trying to keep it in the green zone. However, I am coming out of an ML63 AMG so that is almost double what I used to get

barry1955

In a previous post to this forum, I wrote that I had a habit of topping off the tank whenever I filled up with gas and was averaging 32.5 and 33 miles to the gallon, see below.

"I have a 2010 RX450 with 5100 miles on it. I have been averaging between 32.5 and 33 miles to the gallon consistently since I got the car. I have a habit of trying to "top off" the tank any time I refill it. I was curious if anyone knows how the car determines MPG and if topping it off might be the reason mine is so good ?"

At the advice of others on this forum, I stopped topping off the tank and now at 6350 miles, over 1100 miles since my last posting, my mpg has dropped to 31.5 to 32 MPG. Still a good mpg but obviously not topping off the tank had an impact on it. Nothing else has changed but topping off the tank. Somehow overfilling the tank artifically inflated my MPG slightly.

I am a careful driver, no fast starts from lights, etc. and drive in ECO mode consistantly since purchase, 50/50 combo of highway & local driving in Florida, keep tire pressure alittle high at 37 PSI and am very happy with the SUV and MPG I am getting.

billy44bo

how does it ride at 37psi? and how are the tires doing?

SLegacy99

With as cold as it has been this winter this has really impacted the mileage on our 400h this year. Down to 23-24 MPG and it's typically between 26-30 during the warm months.

barry1955

The car rides great at 37 PSI, I think it actually feels more nimble. I did the same thing on my 2006 RX350 for 50,000 miles with no negative effect on the tires, I actually got alittle longer life out of them.

Cruiter

Some folks complain about bad mileage and others say they get good. It's all about whether or not your trips are long enough to warm up the engine (and cabin with batteries) and whether or not you drive it like you really want economy or drive it for performance.

Here's a graph of my past year for the naysayers.