I believe this is a significant part of the reason why MPG numbers fluctuate wildly in various reports. Usually it's people who are bad at math, or do not calculate over a full tank (worse yet, one partial tank instead of many full tanks), or have something wrong with their car causing low numbers... but after you rule that stuff out, the fuel itself can cause a 10-15% swing.

It took me 2+ years to finally figure it out, after replacing injection pumps with fresh rebuilds on both cars, and replacing injectors with matched rebuilds as well (new nozzles, etc). Wasted a whole lot of time and $$$ trying to figure out why the cars were running so "poorly"... sigh. Of course, if you are not able to locate good/reference fuel to test with, it's not easy to pinpoint.

I was able to average 32.84602283 miles per US gallon, 39.446445 miles per imperial gallon.

5 weeks on the road driving 8795.65 miles driven 20 fills city and highway driving plus mountain, desert and plains driving

Average per tank imperial gallons
36.059
40.482
43.661
36.139
38.283
45.498
40.372
37.854
46.799
33.26
36.972
38.391
39.035
41.981
36.575
39.542
42.487
41.329
40.332
41.08

Usually drove the speed limit plus 5 to 10 mph

Lifetime mpg Includes winter months of up to -40

No disrespect but calculating your mileage on one or two tanks is nearly meaningless as it is near impossible to fill to the same level. It is all to easy to overfill an extra gallon or to under-fill a similar amount.

I find that if I can fill with the driver's side of the car low I can get an extra 2 gallons in. To get reasonable numbers you should average over at least 5 tanks.

__________________
1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250, Dec 2024 145,000 miles

8 decimal place mpg

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I want to know what planes driving is all about? did you hitch a ride on a cargo plane?
BTW that 46.xxxx MPG was probably downhill, with the wind to your back
But I do agree with taking an average of at least 5 possibly 10 fill ups to avg out the anomalies.
I stopped looking at the MPG calculator on my '99 but it was running as high as 32.5 with a little Redline 85 plus added at fill-ups.
DDH

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

The 46 followed by 33 is easy to explain. As I recall crossed into California and with their vapor recovery system it was not possible to fill up normally and the fill was gallons short. Similarly coming out of CA was able to do my normal fills once again and the first tank would have an extra couple of gallons more than CA.

Agree completely with " I do agree with taking an average of at least 5 possibly 10 fill ups to avg out the anomalies."

I expect the above figures to be plus or minus 1% at most over that many tanks and such a long distance. Especially with much attention given to the first and last fills.

__________________
1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250, Dec 2024 145,000 miles

It's not. They both get 32 mpg max.

36
That car will never get 36. If it could, mine would have in 14-years and 131K miles.

Wintertime? Yes. The '99 doesn't get any better than 32 mpg. Anything more is some sort of fluke of a readings miscalculation of what is believed the car gets.

__________________
'06 E320 CDI
'17 Corvette Stingray Vert

Yours specific car & local fuel may not exceed 32, but other people can and have exceeded 32... like KarTek who posted above, typical 34 freeway, 37 peak.

I chalk that up to either modding, or miscalculating mpg. I guess they can claim whatever they wants to, can't they? I travelled over the 1/2 of the Country, border to border and nearly coast to coast in my 99 for years. 365 days a year in all weather and fuel markets. Most ALL HWY miles on the car. If the car as factory built were capable of better than 32, it would have happened as I recorded and calculated every tank-fill. They're not.

One person here claimed 43 mpg driving one. You can believe what ever you choose to but they do not get over 32. Regardless the fantasy "peaks" and outliers claimed.

Shertex's numbers and mine are spot-on for the car.

__________________
'06 E320 CDI
'17 Corvette Stingray Vert

I should start giving my mileage in Imperial MPG; it sounds more impressive .
Yeesh, Skid. Give it a rest... why do you keep on making Ex Cathedra pronouncments about fuel mileage based on one man's experience and then shoot down anyone who gets anything better?

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

The average of 10 or more empty-to-full-tank fill-ups will produce fewer bombastic mpg claims. I recall that one guy around here a year or two ago was claiming 48 mpg with a '99. I got a very good from that claim.

It's not unusual for the 98/99 to yield as little as 18 to 21 or 23 mpg fill-ups too. Totally depends on how, and where the car is being driven. I suggest that driving one for 15-years from new and clocking every tank, as I did, will tell anyone this.

__________________
'06 E320 CDI
'17 Corvette Stingray Vert

So, if your personal car will not exceed 32, it's impossible for anyone else to own the same model and exceed 32. Got it.



Well sure, someone claiming 33% greater MPG than EPA highway rating is clearly suspect. Meanwhile KarTek's data matches EPA numbers almost dead on. Interesting.



18-21mpg? You seriously think that's "not unusual"? That would be along the lines of "major fuel leak" or "frequent racetrack use". But, like, whatever dude.

__________________
Check out my website photos, documents, and movies!

Related note: The EPA ratings for the 1987 300D (yes, I know, different chassis/engine) are 25 city, 30 highway. Over the past 150kmi of ownership, tracking every single fill up, my 124.133 has almost always ended up between those two numbers. The peaks were 32-33mpg, or 10% above the EPA rating. The lowest were about 10% under the EPA city rating.

Translation: The EPA ratings are not THAT unrealistic.

Like a longer period? 74,524.5 miles

2,078.146 Imperial Gallons

Only 96.32% of combined EPA

__________________
1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250, Dec 2024 145,000 miles

Uh, none of 'em will - perhaps you missed that? Got it.




The bombastic numbers above and well beyond aren't reality - but you can believe what you want to.




Seriously? Dude, you are gullible enough to think everybody with a 98/99 E300 gets 37 to 48 mpg?! ALL the time?! Just b/c they posted it?! Seriously?!

__________________
'06 E320 CDI
'17 Corvette Stingray Vert

HWY only. That's a good number - 32.

That's the top-end mpg the car does IME driving the HWY speed limit in most of the U.S.

Again, for the benefit of the non-believer(s) - drive one from new, 15-years and 131K miles then post your (98/99 E300) cumulative mpg numbers:

__________________
'06 E320 CDI
'17 Corvette Stingray Vert