My 87 300D gets 30 to 32 mpg combined!

Can't quote in US MPG figures but I can quote in litres/100km (or even MPG imperial which we stopped using here in Australia 30 years ago).

Our 1990 300TE (M103 with 4 speed auto) with more weight and shorter final drive gearing than 300E or 300CE regularly returns 10 litres/100km (28 mpg) on the highway (at not much over our strictly enforced 100km/h and 110km/h limits) with family and luggage on board.

My father's 1993 E320 coupe (M104 with 5 speed auto) returns around 9 litres/100km (31.5 mpg) under the same conditions with 2 adults and luggage.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The power requirement to maintain constant speed on a level road with no wind increases with the cube of speed, so fuel consumption normally increases noticeably with increasing cruise speed, and typical cars achieve lowest steady state (top gear) fuel consumption at about 35-40 MPH, however, modern cars that have very tall gears that are not useable until higher road speed may have a slightly higher lowest fuel consumption cruise speed.

Various anecdotal evidence such as yours is sometimes presented, and I can only take it with a grain of salt - most drivers don't keep accurate fuel consumption records over a long period of time with fairly constant driving habits, which is what is necessary to draw general conclusions.

Spark ignition engine thermal efficiency varies widely with revs and load from around 30 percent at high load near the torque peak (but less than WOT to avoid power enrichment) to zero at idle. A lot of spark ignition engine loss is the pumping loss associated with manifold vacuum, and the internal friction losses increase with the cube of revs, which means that running tall gears so steady state cruise is achieved at low revs and high load is best, however, offsetting this is the fact that most spark ignition engines have less than ideal spark advance for peak thermal efficiency at low revs and high load, either due to emission requirements or detonation considerations.

Diesel engines have little pumping loss because they are not throttled, and since detonation is not an issue, injection timing can be optimized for peak thermal efficiency at all speeds and loads if the control system is sophisticated enough to provide the required granularity, and their higher compression ratios generate inherently higher thermal efficiency.

Duke

I know that what I said at first glance may not make sense but in the real world we are not driving on level roadways --- perhaps in part - a theory -- I get better fuel economy while cruising at higher speeds because of the momentum gained at level road sections which reduces the engine load at inclines.

As a general rule, fuel consumption on level terrain is less than hilly terrain of the same average altitude.

High altitude level road fuel consumption is usually less than level road fuel consumption at lower altitudes because of the lower air density at higher altitudes reduces aero drag.

Duke

Hi Guys,

My 300CE (M103) in Ireland consistently gives around 28 to 30 mpg, with a best one time of about 32mpg on a long run at around 60-70mph.
Around Dublin, where it used to take me 1 hour to do a 5 mile trip, it was returning about 15mpg, but thats a traffic factor more than the car.
I normally drive sensitively as regards the throttle, but if i need to overtake, I dont spare the welly.

Gerard

1986 Mercedes-Benz 300E

Fuel Economy
Fuel Type Premium
MPG (city) 18 (21.6 / Imperial Gl.)
MPG (highway) 22 ( 26.4 / Imperial Gl.)
MPG (combined) 20 ( 24 / Imperial Gl.)
Annual Fuel Cost 1770

I have 1988 300e, 194ks... normal highway driving at 110kph constantly gives 10lt/100ks... never checked town driving but does use much more fuel...

I get 20 in mixed driving. Just did my first road trip..all highway, got 25 mpg

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

On average I get about 20mgp with about 40% city and 60% highway. My driving habits are not very fuel efficient.
Bruno

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1992 300TE 160 kmiles