How Accurate Is Your Mpg/tank Avg. Readout?

[dk63]

I've had my IS250 for a month now and the first time I had to fill it up the computer readout said my average MPG for the tank was 27.9 MPG. When I did the manual calculation of miles driven/gallons filled I came up with 25.5. This morning I filled up for the second time and the readout was 30.5 MPG, but the actual calculation came to 27.9. I'm not complaining about the MPG I'm getting since the Pathfinder I got rid of only got 17-18 MPG, but it seems the computer does a lousy job of calculating since it's 2.5 MPG off. Anyone else have this same issue?

[smooth1]

I've been wondering about the accuracy, but I haven't checked it yet. I usually set the trip odometer to 00000 then fill up the tank. The next time I fill up, I just look at how much fuel went in, and what the odometer says, and do the math.

How are you doing the "manual" calculations?

[lambobaby1218]

There is a thread in here somewhere on this. The computer is not as accurate as it should be. My car consistently gets 26 mpg. Although it may start changing since I started slowing down. The computer has told me it's getting 28 mpg.

[dk63]

I've been wondering about the accuracy, but I haven't checked it yet. I usually set the trip odometer to 00000 then fill up the tank. The next time I fill up, I just look at how much fuel went in, and what the odometer says, and do the math.

How are you doing the "manual" calculations?

I calculate it based on the number of miles since my last fill-up divided by the number of gallons pumped. In the case this morning it was 409 miles and 14.63 gallons.

[bartkat]

The computer number is more of an estimate. Mine is usually about 1 mpg lower than my calculation. You really can't get an accurate figure on just one tank anyway due to the variation in your fill up level. Best way to get overall mpg is to do it over 3 or 4 tanks. That takes out some of the error in filling.

[IS 4 EVER]

That is great My 350 is 17.8 but I am pushing every thing this can give today I took an evo8 by a full car length and this thing is still stock woohoo cant believe this thing, had a friend in the car and at 130 he said he was going to throw up if I didn't slow down I gave him a bag and said shut up or get out. Anyways this car is a rocketship quite a difference from my previous is300 that was dynoed at 238 horse at the rear wheels. but to get there I played and spent many dollars.

[Rogerm]

Make sure you "reset" the mpg ( hold the display button down) after you do your next refill ...

If you don't it is a total mpg based on your total mileage ... since your last reset.

[bartkat]

Make sure you "reset" the mpg ( hold the display button down) after you do your next refill ...

If you don't it is a total mpg based on your total mileage ... since your last reset.

MPG per tank resets when you fill up.

The other MPG readout is since the last reset.

I've got 22.1 MPG on mine for the last 10,000 miles.

[Motoracer]

My IS350 gets about 1 mpg better than the computer estimate. With gas prices near $4 and a really boring exurban commute, I've been working on efficiency. Without resorting to hairball techniques I can get 25 mpg on a 50 mile commuting loop with 25 stoplights and an average speed of 30 mph. Not bad considering 300 hp on tap for those rare occasions when it can be used.

[tex2670]

I find the car is about 1-2 mpg optimistic.

[PoolGuyMikey]

I find the car is about 1-2 mpg optimistic.

I've got a 2007 IS250 RWD with 23000 miles. My total MPG is 23.0 (computer average, mixed driving (freeway and local)). On the few long trips I've taken, the computer average is over 30. When I've checked the mileage manually, the computer is consistently about 2 MPG over actual.

[foxwiz]

I've had my IS 250C just over a month and it's rated at 21/29. Two weeks ago I took trip from Los Angeles to San Diego, about 150 miles. I reset the mileage gage and when I arrived in San Diego I got 33.9 MPG. Granted I left home around 6 AM so there was no traffic and I was pretty light on the gas.

In normal street/highway driving I get an average of 26.

Love the car and since I've purchased it, I haven't seen another one yet!