: Mpg



Cowboypilot
08-26-10, 11:54 AM
2005 STS V-6 un modified. 74K miles.
Just bought the car and thought I would test the actual MPG vs the onboard computer.
I topped off the tank, got on the interstate, set ctruise at 75mph, for 58 miles. Had to tap break once to 65, then slowly accel back to 75 for rest of test. Gas station at the end of off ramp. Topped off tank..2.37 gal 24.4 mpg using the old fashion way..Computer showed 24.2 avg MPG, 2.4 GAL USED, and avg speed of 67( had 1/2 mile of service road to on ramp and stop sign on end of off ramp).
That is accurate.
Next test will be all driving (mix city and highway) over the course of 3/4 tank. t
Then a 200 mile leg doing 80-90 when able will report back.

My old 1999 Accourd V-6 got 22 city and 25 HWY and 21 at 80-90 hwy.

MacMuse
08-26-10, 03:44 PM
Congrats on the purchase!

I always like a good MPG thread, even if it just exposes my low numbers. Here's my current data on my N* for the past full year.

http://i20.photobucket.com/albums/b215/MacMuse/CAR/e5648dc5.jpg

and the numbers behind the pretty picture...
http://i20.photobucket.com/albums/b215/MacMuse/CAR/a52db5ab.jpg

I frequently see about a 1 gallon discrepency between the pump reading and the car's 'Gal Used' reading on full refills. The reported v. calculated mileage differs slightly accordingly.

doowap57
08-26-10, 03:53 PM
That's about what I get with mine. Tires set +2 lbs, @ 32 PSI, just for LONG trips.:patriot:

EChas3
08-28-10, 06:19 PM
Both our cars DIC MPG are a little optimistic. I was just out for some WOT runs; oh how that engine sings!

That & 100 miles of city expressway driving displayed 17 MPG. I got 16 when calculating by hand.

In my mind the N* can be reasonably effcient 2,000 RPM and under. That's about 60MPH in my 1SG and 80MPH in my wifes car. Above that, it's not so efficient; but fun!

BaTu
08-28-10, 08:17 PM
Maybe the real cure is just a cap you plug into the lighter socket ;)

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200512081938

next2pool
08-30-10, 01:27 PM
Maybe the real cure is just a cap you plug into the lighter socket ;)

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200512081938

WOW--I thought I had seen it all :)

bbshriver
08-30-10, 03:48 PM
I've measured mine a few times and always found the DIC to be within 1mpg of calculated.
How does the car calculate the "gallons used"? I thought that the cars calculation would likely be better than mine, since I figured it would take the data from the FI system usage. Any ideas?

On 100% pure highway I have gotten 26-27mpg in my N*. I've got the 1SF though with 2.73 rear.

next2pool
08-30-10, 04:08 PM
I've measured mine a few times and always found the DIC to be within 1mpg of calculated.
How does the car calculate the "gallons used"? I thought that the cars calculation would likely be better than mine, since I figured it would take the data from the FI system usage. Any ideas?

On 100% pure highway I have gotten 26-27mpg in my N*. I've got the 1SF though with 2.73 rear.

Yes--the computer calculates the injector spray amount so it is very accurate. If I had to judge the hand calculation vs the computer calculation, I would take the computer since it doesn't have variation on fill levels and potential round off issues. Over time, though I think they will come out the same. Depending on the car, the computer calculation duration is different as well. I would reset the the average mpg at every fill of course if you are comparing.

bbshriver
08-30-10, 04:12 PM
Thanks for the comment.
I'd always wondered at people who "don't trust" the DIC, or say it's optimistic.
If anything mine should be a tad pessimistic, as my tires are slightly larger than stock, and my speedometer (so presumably my odometer) reads about 3% slow.

Could potential "optimisim" of the DIC be related to anything like fuel evaporating in the tank, etc? i.e. if you routinely put more gas into your car than the DIC says it's used, the extra fuel has to go somewhere?


Yes--the computer calculates the injector spray amount so it is very accurate. If I had to judge the hand calculation vs the computer calculation, I would take the computer since it doesn't have variation on fill levels and potential round off issues. Over time, though I think they will come out the same. Depending on the car, the computer calculation duration is different as well. I would reset the the average mpg at every fill of course if you are comparing.

next2pool
08-30-10, 08:56 PM
Thanks for the comment.
I'd always wondered at people who "don't trust" the DIC, or say it's optimistic.
If anything mine should be a tad pessimistic, as my tires are slightly larger than stock, and my speedometer (so presumably my odometer) reads about 3% slow.

Could potential "optimisim" of the DIC be related to anything like fuel evaporating in the tank, etc? i.e. if you routinely put more gas into your car than the DIC says it's used, the extra fuel has to go somewhere?

Some fuel wiil go into the evap system, but that is minor and should be accounted for. As to where is the fuel going, I suspect it may take months for the manual calculations to be meaningful. As the graph that another member showed, day to day economies and fills can be all over the map. Given all that, there will be some errors on each end including normal accuracy of the pumps.