Thoughts on the MPG Variance and Data Gathering

[DrJon]

Could be that a pump (supposedly accurate by state standards) was off also?

[DaveinOlyWA]

Originally Posted by DrJon

Could be that a pump (supposedly accurate by state standards) was off also?

Costco is where i got the gas and although the state mandates pumps be calibrated every 3 years, Costco calibrates theirs every 6 months. they acknowledge that the mechanics of the pumping system do wear out and becomes inaccurate, so they take on the expense to go the extra mile to make sure the pumps are accurate.

the last time i went there which was last week for the SPM, i checked the their inspection stickers were dated 06/2009...

[billklug]

Just got "Bullet" out of the shop with a new paint job. Weather changed and 104F required AC to be run. AC appears to tank my MPG from historical 53 to about 46!! Perhaps I should just sweat and go for the better MPG?!? Will perform and experiment relative to AC on vs. AC off and see what the delta is; will report back.

[DaveinOlyWA]

OP edited with latest tank. think i probably short-filled the previous tank which accounts for part of large discrepancy on this one. last tank shut off 3 gallons to early, so filled it to estimated level of fullness. lost first bar at around 80 miles i think which is far less than normal.

[alfon]

I can not pump my own gas here in Oregon, and there is a new law where once the pump clicks off you can not top off by law.

However, if I lived in a state where you could pump you own gas; I would fill to the top of the neck where you can not get any more gas in. Than I would drive say 500 miles or so. Fill up, at the same station pump, to the top of the neck. Look at what the MPG display states, than calculate miles driven and gallons used.

In my opinion this would give you a very accurate reading, and after a few tank using the same method there would be no discrepancy.

I know that there may be problems with the charcoal canister by filling up to the neck, but who here has any problems by doing that?

alfon

[anne1965]

Originally Posted by billklug

AC appears to tank my MPG from historical 53 to about 46!! Perhaps I should just sweat and go for the better MPG?!?

Do you make short trips or long? On short trips the A/C hit is large because it goes flat out to cool the interior, and then throttles back when the set temperature is reached? If that moment coincides with the arrival at your destination...

At what temperature do you set your A/C? I usually set it at 23 C (73F I believe), I have read from others setting it as high as 78 F. This does make a considerable difference in the Prius.