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  #1  
Old 04-25-2013, 10:41 AM
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Real-World fuel mileage

As promised:

Car is 1983 300CD. Fresh oil change with 15W-40 AMSOIL. Fresh valve adjustment. Fresh air filter and fuel filters.

Starting miles: 290788. Ending miles: 293341
Total miles driven this trip: 2553

Trip route:
Leg 1: Near Richmond VA to Tampa, FL via U.S. 1 to U.S. 301 (no interstate hwys)

Leg 2: Tampa to Ft. Lauderdale. No interstate hwys
Car parked in Ft. Lauderdale for 5 days.

Leg 3: Ft Lauderdale to Charleston, SC. No interstate.

Leg 4: Charleston SC. to Home. Interstates all the way at speed limit (65 to 70 mph).

Air conditioning most of the way, cruise control used where feasible. Ran speed limit. Did not avoid small towns.

Fueled 10 times (kept at 1/2 full).

Threw out the high mileage and the low mileage and averaging the rest provided a real world mileage of 29.456.
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Old 04-25-2013, 10:48 AM
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why would you throw out any mileage?

I'd total the miles, and total the gallons, and that would be my mileage for the trip.
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  #3  
Old 04-25-2013, 11:17 AM
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I did 63mph on a 2 hour trip and got 32mpg.


What color is your CD? I saw a white one in town a few days ago (charleston)
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  #4  
Old 04-25-2013, 12:21 PM
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Keep in mind that tire size affects "indicated" speed and miles. So as your tires wear (get smaller), your speedometer and odometer will err on the high side. This is most notable right before and after you get new tires. So basically, if you are using your odometer to measure miles traveled, it is likely an overestimate if your tires are worn. This is one of the reasons some here suggest using GPS to accurately determine miles traveled in mpg calcs.
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  #5  
Old 04-25-2013, 01:30 PM
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Quote:
Originally Posted by rocky raccoon View Post
As promised:

Car is 1983 300CD. Fresh oil change with 15W-40 AMSOIL. Fresh valve adjustment. Fresh air filter and fuel filters.

Starting miles: 290788. Ending miles: 293341
Total miles driven this trip: 2553

Trip route:
Leg 1: Near Richmond VA to Tampa, FL via U.S. 1 to U.S. 301 (no interstate hwys)

Leg 2: Tampa to Ft. Lauderdale. No interstate hwys
Car parked in Ft. Lauderdale for 5 days.

Leg 3: Ft Lauderdale to Charleston, SC. No interstate.

Leg 4: Charleston SC. to Home. Interstates all the way at speed limit (65 to 70 mph).

Air conditioning most of the way, cruise control used where feasible. Ran speed limit. Did not avoid small towns.

Fueled 10 times (kept at 1/2 full).

Threw out the high mileage and the low mileage and averaging the rest provided a real world mileage of 29.456.
Rocky-
I thought you went to the Black Hills of South Dakota? Say hello to Nancy.

Seriously, that is a great mpg figure!
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  #6  
Old 04-25-2013, 02:19 PM
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I refrain from posting mileage results generally, as I seem to pull down mileage results that might result in me being tarred and feathered by the community. That said, the '83 turbo drivetrain in my '77 300D prior to my 4-speed conversion was accomplishing 29 MPG consistently with about 25/75 city/highway. Odometer verified with GPS.

I figured I would just keep my mouth shut and enjoy it. I am hoping that the 4-speed conversion will bump up the fuel mileage a little.

If you will excuse me, I need to go spray myself with WD-40, so that the tar and feathers won't adhere as well.
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  #7  
Old 04-25-2013, 03:19 PM
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I drive 80+ in my wagon which is probably in need of a valve adjustment and the new nozzles I have on my work bench... Toll roads for 12 miles/day and a mile or so of stop light traffic.

I get about 20mpg. Right foot is HEAVY.
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  #8  
Old 04-25-2013, 05:30 PM
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responses

vstech: High mileage was unrealistically high and low was unrealistically low. May have had to do with fuel fill but tossing out high and low when averaging is a common statistical technique.

shorts: tires are about middle-aged but in any case, I think the difference would be within margain of error.
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Old 04-25-2013, 05:39 PM
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You need to at least check your odometer against mile markers or GPS. My odometer reads 10% high even though the speedometer is spot on. I have to multiply my indicated mpg by .91 to get true mpg.
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  #10  
Old 04-25-2013, 10:12 PM
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Quote:
Originally Posted by rocky raccoon View Post
vstech: High mileage was unrealistically high and low was unrealistically low. May have had to do with fuel fill but tossing out high and low when averaging is a common statistical technique.

shorts: tires are about middle-aged but in any case, I think the difference would be within margain of error.
Rocky,
Its called removing outliers.
An outlier is a value that is more than 1 1/2 X IQR from the nearest other data point. You may have over done it a bit.
At least you made the effort to use figures over a long distance. There are way too many on here who quote numbers from topping up their tank after a few short trips.
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  #11  
Old 04-28-2013, 12:31 AM
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Well, it's almost exactly 200 miles from my home in Alexandria to my parent's home in Virginia Beach. My 5-speed NA 84 TD has an incorrect replacment speedometer for a turbo model. So, using the interstate mile-markers to calculate the correction-factor, on my last trip I got around 30 mpg highway, with the AC going, at an average 65 mph. This includes the few miles in local traffic when I left Alexandria and just before I arrived in Virginia Beach.
I'm hoping to make the same trip next week and retest, hopefully without needing the AC this time, as it needs a new LP hose and freon now, and after some brake work, since lately my front brakes have been dragging.
Unlike the typical eBay W123 peddler claiming 40+ mpg, 30 is not an outrageous figure for these cars.

Happy Motoring, Mark
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Old 04-28-2013, 12:57 AM
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Quote:
Originally Posted by rocky raccoon View Post
As promised:

Car is 1983 300CD. Fresh oil change with 15W-40 AMSOIL. Fresh valve adjustment. Fresh air filter and fuel filters.

Starting miles: 290788. Ending miles: 293341
Total miles driven this trip: 2553

Trip route:
Leg 1: Near Richmond VA to Tampa, FL via U.S. 1 to U.S. 301 (no interstate hwys)

Leg 2: Tampa to Ft. Lauderdale. No interstate hwys
Car parked in Ft. Lauderdale for 5 days.

Leg 3: Ft Lauderdale to Charleston, SC. No interstate.

Leg 4: Charleston SC. to Home. Interstates all the way at speed limit (65 to 70 mph).

Air conditioning most of the way, cruise control used where feasible. Ran speed limit. Did not avoid small towns.

Fueled 10 times (kept at 1/2 full).

Threw out the high mileage and the low mileage and averaging the rest provided a real world mileage of 29.456.
That is about what I would expect that car to get @ 70 mph, HWY only. That's reality - under THOSE conditions.

Quote:
Originally Posted by vstech View Post
why would you throw out any mileage?

I'd total the miles, and total the gallons, and that would be my mileage for the trip.
Because the high and the low were outliers - they were not accurate from an average mpg standpoint of 10 fill-ups, as stated. With that many fill-ups, it would be advisable to throw 'em out anyway, leaving 8 check fill-ups. That's plenty.





Quote:
Originally Posted by andrewjtx View Post
I drive 80+ in my wagon which is probably in need of a valve adjustment and the new nozzles I have on my work bench... Toll roads for 12 miles/day and a mile or so of stop light traffic.

I get about 20mpg. Right foot is HEAVY.
THAT, is a reality number.



IN general about mpg here:
Call me skeptical, or trying to keep it real, but after 5+ years here, I routinely read claims of 41 to 44 mpg @ 65 mph with my identical '99 E300TD diesel car auto here on DD. It is a physical impossibility to get 44 mpg out of a car that will not get out of the LOW 30s, unless it is covering those miles being pushed or towed with it's engine off. I get my hip waders out when I read mpg claims that a like car will physically return beyond 32 mpg under any real world conditions. If my car and an exact like car were to be able to return ANY better mpg @ 60 to 70 mph than 32 mpg, ithey would have already done so in 14-years, AND 130K miles since buying it new.
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Last edited by Skid Row Joe; 04-28-2013 at 01:24 AM.
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  #13  
Old 04-28-2013, 03:27 AM
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75 MPH on the highway.
Sorry if I don't immediately believe you.

Is anybody else getting even HALF that?
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  #14  
Old 04-28-2013, 07:12 AM
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highest and normal on a trip

My highest one time was 34, but I had 8 quarts atf in the tank.Normally I add one bottle of Marvel Mystery oil to a tank,and average 32.I do it to keep IP lubed up.
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  #15  
Old 04-28-2013, 07:31 AM
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Quote:
Originally Posted by oldsinner111 View Post
My highest one time was 34, but I had 8 quarts atf in the tank.Normally I add one bottle of Marvel Mystery oil to a tank,and average 32.I do it to keep IP lubed up.
When you had 8 quarts of ATF did you add two gallons to your fuel quantity before calculating?
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