|
|
My son has made a couple of runs to Georgia and back from upstate NY this Fall, and is puzzled (as am I) about his mileage. He is quite car savvy, and tries for consistency with fill-ups, etc., but can't account for the variations he gets on consecutive tanks.
These variations don't seem to correlate to weather, wind, or terrain, and have been noted on ~600± mile runs in both directions on I-81.
He used to get 30± on trips in the '83 turbo wagon with M46, so I don't believe it's his driving habits. This '87 Auto wagon is a nice-runing, with about 230K miles on it.
He's heading South again in a couple of days.
Any ideas?
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
|
|
-
|
|
|
You simply can not fill your tank consistantly to get meaningful mileage information from any single fill. If you want to figure your mileage with reasonable accuracy 1)fill your brick at your favorite station and stop filling when the pump turns off 2) drive at least 500 miles adding gasoline as needed 3)return to your favorite station and refill your tank at the same pump used in (1). Take care to park in the same direction and to have your vehicle loaded the same way. Again stop filling when the pump turns itself off.
|
|
-
|
|
|
I'm apt to suggest what's happening at the gas stations where he stopped to refuel. Two main things are:
1) the quality of the fuel, viz. water contamination; addition of requisite anti-ozone additives (ethanol, BT-whatever, etc.), which change the BTU content of the fuel; and even octane, which, given the knock sensors in our engines, would change the timing (maximum advance) and thus have a big effect.
And especially because he's covering a lot of geography (NY-GA), there are also big variations in the fuel itself regarding, e.g., temperature (volatility formulated for coldest anticipated temperatures).
2) I've found a lot of variation between one pump and another at my regular gas station -- one cuts off the flow much earlier (maybe $2.00 prematurely) than another. Does your son manually fill to a know point (where I see the fuel briefly pool above the "unleaded" restrictor's door), or just let it kick off automatically and then just stop there?
|
|
-
|
|
|
Bruce, Two weeks ago I made a trip to Chicago from Charlotte and back.I had the same variations as your son got.I haven't figured it out either.The 88 wagon has a M46 with a 3.73 rearend,one thing I did find that was the RPM's on the mileage,at 26 to 2700 rpms my mileage was worse.When I drove at 29 to 3000 rpms my mileage was better.I keep a complete fuel milage report for the whole trip and the findings were 26.5 to 30.5 mpg's I have cruise control so I know about the the difference in the RPM's on this fuel mileage.The one thing that has me stumped is that I would have thought that the lower the RPM the better the fuel mileage should have been,but that was not the case.The head has been pulled off the car a year ago and was gone all the way through.The head has had everything done to it,and it was ported and polished with a T cam. Ask your son about the RPM's and does the car have cruise on it ask him to make a note on where the RPM's are at for the fuel mileage.
Thanks
Rodney
|
|
-
|
|
|
I've noticed the same thing on my 91 240 NA. I swapped up to an A cam, from the M cam and almost instantly got better gas milage on long hauls. I attribute this to the fact that now I am going 80mph at 2700rpm, and not 65 at 2700. So I am getting more bang for my buck, or I am getting more distance for my buck.
I did notice at 80-85mph I was getting roughly 25mpg and at 75-80mph I was getting 27mpg.
Obviously there is an efficency curve(a bell curve), and it looks like on am A cam with an M47 the top of the curve is around 75-80mpg or 2600-2800 in 5th.
Just moving up or down the curve, from the max point, will result in a decrease in fuel efficency. In the 70/80's american cars were built with this point around 55mph, the max legal speed. But now people are driving around 75mph, so the car is not nearly as efficent.
--
85 240DL 189k; 91 240 169k; 98 S90 110k; 98 S70 160k
|
|
-
|
|
Any idea what the results would be using a 'B' cam on a B230F?
--
'80 DL 2 door, '89 DL Wagon
|
|
-
|
|
|
Your results are going to be about the same, though slightly lower. The A cam is a little more agressive than the B cam, but not by much. Both cams are going to be an improvement over the M cam. When I made the swap I went ahead and cleaned my intake manifold and my throttle body, which accounts for some of the increase.
The M cam is going to beat an A or B for around town driving (fuel wise) but will loose out for long trips at 65+mph.
--
85 240DL 189k; 91 240 169k; 98 S90 110k; 98 S70 160k
|
|
-
|
|
|
hi bruce
on my new/old 740 i caught the odo not adding up all the miles.
but a long shot as you know the distance of the trip.
im suprised the auto is getting 30 mpg.
good luck
mike
|
|
-
|
|
|
Bruce, a few quick thoughts.
- ox sensor
- plugged cat
- stuck valve in air box
With the cat restriction, it could be blocked on/off...? As I say, a few quick thoughts.
Since it's intermittent, it doesn't sound like the other 2 I mentioned above.
--
Norm Cook; Vancouver BC; 1989 745T 210,000KM
|
|
-
|
|
|
Oxegenated winter gas?
--
Bruce S. near D.C.
|
|
-
|
|
|
That's my guess - is he filling up with the same brand? I wonder if the ethanol content of winter gas varies enough between brands to account for it. I've had some pretty dramatic variations in mileage over the past month or two, and have used several different brands/stations, I think that probably accounts for part of it.
--
Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina
|
|
-
|
|
|
I keep detailed records, and since the first of Dec., my mileage has dropped from averaging 25+mpg, to 21.5mpg under the same driving conditions. I would guess that the winter gas has come 'on line', after being delayed because of the problems with the oil refineries after hurricanes Katrina and Rita.
--
Gary Gilliam Sumerduck VA, '94 940 na Regina 160k '86 240 190k, 93 Camry 4cyl 5spd 245k
|
|
-
|
|
|
Could be more or less accurate gas pumps at different fill ups? Bad gas, water in the gas? Dan
|
|
|
|
|
