No More Oldsmobiles

Background: I have kept a mileage spreadsheet since getting the 8. For the first several months I would go nearly to empty before filling up, to get a more accurate reading. My mileage has been in the mid-19s to 20 mpg. And until recently, I never filled up when it had more than a quarter tank.

The other day I topped it off while running some errands. It was just 3.186 gallons. I had gone 53.8 miles. Meaning I got about 16.9 mpg.

Gasoline is heavy, so we get poorer mileage with a full tank than with a quarter tank. I wonder if people who get fewer mpgs fill up more often.

(Note: I stick with brand-name gasoline -- Shell, Exxon, BP, etc., never using ecomony brands, and always 93 octane.)

MP3Guy

Gasoline is about 8 lbs/gallon.

I dont think 24 lbs extra weight killed your mileage. Most likely you were doing the Doo-Wah-Diddy with the throttle, you lucky dog!

nzarnow

some day, you will have to tell me what the hell that is....

No More Oldsmobiles

You're being a lot more ambitious than me. All I have is gallons, miles on the trip odometer, price and mpg (though I've saved the receipts and could go back and add brand.) In other words, just the basics for figuring your mpg. Yours sounds pretty interesting, though. Let us know if you find something.

(MP3Guy, true, maybe it was just my driving for those 50 miles. This was the first time I had ever topped it off, and I was really struck by the difference in mpg.)

loco4rx8

Interesting. I, too, have a basic mileage spreadsheet that I've kept since I got my car. However, the two times that I've filled up with less than half a tank gone, I got very good gas mileage (3.9 gallons in, 23.56mpg and 7.2 gallons in, 22.97mpg).

Oddly enough, over the last month, my mileage has definitely been trending ... up! My overall average since I bought the car is 22.72 mpg. But over the last month I've averaged 23.54 on five fillups.

What's different, you ask? I got the N flash and 35,000 mile service (which includes new spark plugs) at the beginning of the month. I wonder which of those two things (spark plugs or N flash) has had the most effect.

And I don't mean to hijack your thread, No More Oldsmobiles. Just didn't want to start another new mileage thread for fear of getting yelled at.

schrottie

On a german RX8-forum that I read regularly there was a mile-long thread about some 8s' oil beeing cooled to the point of the ecu trying to warm the engine. This was supposed to explain the poor mileage some folks, including myself (14,5 mpg) are getting.
I never gave much about it, but we now had the first real summer days and guess what: As the temps went up, so did my milage.
Anybody with similar observations?

BlueFrenzy

^^^ I agree with you Schrottie with regards to the cold climate mileage. In minus 25 Celcius weather, it takes a good 5-10 minutes before the temperature gauge gets to the halfway mark. So I assume that during this time the engine is running richer. I've noticed that the engine idles higher too (around the 1500 range). Also don't for get winter additives could also affect the mileage.

Back on track, I actually found the opposite of LocoRX8. The times that I did fill up early (ie with halftank or more), I found the mileage to be poor. It seems in my car, that the 2nd half of the tank gets used up slower (this is purely based on watching the gas gauge in relation to distance ... no real science to it ... just like my *** dyno).