I been checking my mpg last 2 days ? LOOK
 

Also i went 29.5 miles round trip to work Monday. Before.i.left home the tank was filled to the.top of the neck.i got home added. 1.25 gallons of fuel =23.6 mpg in town.

Today Tuesday..i went same route to work and home same miles 29.5 got home added .75 gallon = 39.33 mpg.

my odometer says 29.5 miles
my GPS says ... 28.5 miles...i trust the GPS better right ???

the only thing different i did was lube/moly purge the injectors ,replaced the main and pre-filters adjust the transmission cable was shifting out to soon on Monday bogging ..the ALDA is turned 1.5 turns in from all the way way to the stop position.
still have to adjust the valves too.

i still got to get a tire pressure gauge,to check tire pressure, also i need a front end alignment i got some neg. camber.

the way i been checking it is fulling the tank to the top of the neck all the way ...and when i get home i got a 1 gallon can i pour in it .
i know this isn't the correct way...but shouldn't the way i did it be close to what i travel a day ?
i know i need to run a whole tank soon then check it .

i just got this car ,and just got it road worthy.and that was with the c/a on too. plus i didnt go over 60 mph. to work is mostly no traffic at 5 am. way home does have some stop and go a lot at slow speeds.

sorry for the wording ,,M.S & O.C.D.:o

What car are you driving? I find 39mpg to be a little outrageous. I would bet the tank wasn't filled to exactly the same level both times.

whiew! that looks like a lot of difference, but on such a short drive, a burp in the tank could account for the difference.
you may have hit the lights better on the second trip. traffic pattern change, monday vs tuesday traffic...

o sorry it's a 83 300d . i filled the tank up to the neck at night in the morning before starting the car, i would top it off ,it just took about A cup full, when i got to work at 12.8 miles i could still see the fuel barley in the bottom of the neck,but still in the neck..thats the fairly straight shot to work they to have 25 stop lights but mosty i catch 5 to work. mostly cause they are timed at that time,
on the way home theres alots of let me see...left...right....left....right....left.....right.....right.....left...

to work is left ....right..right...left u turn right at work.

if i go by gps miles of 28.5 thats still 38 mpg.

after i ajudt my valves,replace both my rear axle shafts>got.

i made a thread on swapping to a 3.69 gear remember ? i might not want to do that now ?

i could see what the differance is , it doesn't take me long to swap out diff's and back again

but @ 70 mph rpms are 3500 with 3.07s
@ 60 mph is 2950 .
@ 45 ................. 2000 .

Car is a automatic..with 156k on it.

car felt like it was luggin on monday thats why the purge and filter change.trans was shifting out way soon also.

i just wanted to get 32 mpg to work and back
i thing highway mpg would be less cause of high rpms ? correct.?


iam going to check it once more tomorrow .same way . hopefully i dont have to run anywhere else after work to throw my readings off.

Need a few tankfuls combined to get any form of meaningful average. I just top off my tank and set the trip odometer. After several fill ups I refill once again and divide the fuel used in gallons into the accumulated miles.

This tends to give me a ballpark average. There are just too many variables otherwise. As soon as the weather changes or the driving style or the length of trips and speeds etc. That figure goes out the window as well.

Ran the 85 300D about 1000 miles over the weekend. 95% highway miles, loaded down with wife and 3 kids plus the trunk so full we could hardly close it. It averaged 31.7mpg. I double checked it with GPS and also found that my odometer is correct and the speedo is reading correct.

It would be really close to impossible to get any meaningful data out of short run mileage figures using a strategy of refilling the tank to the same level. As has been suggested, you really need to do this over several tanks. Just the expansion and contraction of fuel volume based on temperature change would have a significant effect on short term data.

Some of the mileage computers that come with cars today do a pretty good job at providing fairly meaningful information, provided they are calibrated to actual long term data using corrected mileage and pump gallons. (You can't actually calibrate them, but you can get a percentage deviation from actual that can get you to a meaningful number)

My Corvette C5, for example, does a very fine job of providing fuel mileage data.

Years ago I put a Perkins 4.108 diesel in a Chevy Vega and installed an after-market performance computer that did a pretty good job as well. It used magnets and a Hall sensor on the driveshaft for distance data and used an optical sensor on device installed in the fuel line that got fuel usage data by counting the times a little ball went around in a clear plastic race as the fuel went through it. It was designed for carb vehicles that did not use a fuel return line. So I had to use an old Holley Carb float bowl to take the return fuel from the injectors which allowed a single line from the gas tank to the engine compartment. (The fuel recirculated from the float bowl back to the engine and I was thus able to measure only the make-up fuel from the tank for the mileage calculation) As a generic computer, it had to be calibrated in order to provide meaningful data, but once set, it actually worked pretty well, even for short distance mileage calculations.

I agree, run a few full tanks through it ....

Also fill at same pump facing the same direction, that keep the tank at the same level of "level"

my odometer says 29.5 miles
my gps says ... 28.5 miles...would you ''trust'' the gps better right ???

im going to put some 15inch rims on it prob. on wed after work to see if i can can speedo closer there tires the size of a 91 560 sel.so are taller .

putting a 2.88 speedo head will make it read faster right ? more miles than before ?

faster and more miles are different statements, the 2.88 will cause the car to travel further than the 3.07 odometer reads.

The problem is that mileage varies with speed. With small amounts of fuel, slight variations if your fill point effect calculations. Drive a few weeks then calculate mileage if you want an accurate all around figure.

There are tire size calculators that show the effect on speedometer reading of changing tire size.

I was thinking about that after i posted....i would need smaller tires ro make to correct.but has org. Size tires.

Whats the part # on the bottom of the speedo head on an 3.07 gear ?

And whats the # on the 2.88 one ?

Thanks

I would be skeptical when ANY of you say your w123 300d Automatic gets 30mpg+ !(unless you are hypermiling, windows up, 45mpg, no AC, no stops, curves, or hills)
BUT with that said if you are AND have registered multi tanks and verified with GPS then I wanna know your secret!!!

NEVER did ANY of my w123 300d's get into the 30's!

I've hit 31mpg with my 4-spd 240d's commute to work. Top speed 50mph & no AC. Then the next week 24mpg 70mph AC blowing high.

'83 300D
 

I have to agree with HIP . . . I've never seen anything close to 30 mpg on the Avocado . . . .maybe 28 on a good day, on the freeway, driving top spd of 65. However, I have heard that swapping a 4-spd into it will up the mileage . . .granted. Otherwise, I want to know your secret!!!! My '83 could certainly use to bump in fuel mileage.

Also, go an entire week and fill up the tank. That will give you much better idea of your true fuel mileage.

Im not sure I understand your fuelling process. You fill the tank at night and the morning with a jug?
Its confusing exactly what you are doing. 38mpg would be a good in town fuel economy for a VW econo-diesel, almost unbelievable for an old MB cast iron 5cyl and 2 ton car.

Why don't you measure the exact distance you travel, IE, work is such and such miles away. Then fill the tank, add up the miles you drive all week, then fill it again at the same fuel pump. Then calculate gallons needed to refill the tank vs miles driven that week.