Gas mileage test
 

Just took a run from South Florida to New Orleans in the 95 e320

First tank: 93 Premium 23.1 miles to the gallon

Second tank: 87 Regular 23 miles to the gallon

98 per cent of the driving was interstate. Speed probably averaged about 78 miles an hour.

I drove off the first tank, my wife the second.

Car ran the same with both grades.

This car usually gets mid grade.

hello lee,

recently took a 300mile trip with the 1993 300e 2.8L, 4passengers total + stuff,
mainly highway driving at 80mph(cruise control) and got roughly 100-105 miles per quarter tank according to the fuel gauge. i believe that the fuel tank capacity, not including reserve= 61L or 16.11US gallon, so each quarter tank is approximately 4us gallons. 100miles on 4gallons comes out to about 25miles per gallon. fuel used = 95octane.

in the past , i have noticed that when using 100octane that the miles per gallon do improve, but have never bothered to do the math and try and figure out if the improvement in mpg's is justified by the increased cost of the 100octane gas.

on a side note: my city mpg's are horrible 15-16mpg

if you'd be interested in tracking mpg's and trying to figure out if its worth using a higher octane gas let me know, i 'd be willing to contribute.

I would've expected 26 to 29, which is what I got on my 95 W124 highway. I will use my Kreskin hat to predict that you are a low tire pressure guy.

My W210 V8 gets 21-22 all the time in mixed commute driving, 26 highway. My 2011 Dodge van with the new 3.7 got over 28 Tampa-Boca with all the kids plus a dachshund (OK, averaging 67 mph). Just raising the bar.
Tom

I get 28.5 with mountain 2 lane driving.premium fuel speeds 65.

same mileage on the way home.... i will check the tire pressure and report back

Yeah, 23 mpg sounds low for that kind of a drive. You don't get better driving conditions than Florida's Turnpike/I75/I10. I did part of that trip (round trip West Palm to Pensacola) and averaged 25.2, and that's with the lower gearing on the 260E.

hmmm low MPG's can be from a lot of things.
tires, brakes, alignment, not to mention plugs, and such... oxygen sensor etc...

Octane isn't nearly as critical as people make it out to be on these cars.

Lee you are trying to cut corners with a Mercedes. They were engineered for premium fuel only! You will find out in the long run.

we've had a long run with mercedes. six 124's and a 108 with the 4.5. that needed premium.

the 124's do just fine on mid grade.

i did have very low tire pressure. change oil, tranny fluid, fan bearing bracket, etc before a long trip....and forget to check tire pressure..... oh well.

Octane is ONLY related to compression ratio. Period. If the engine calls for a certain octane, use it or it may cause engine damage. Detonation and pinging are not always heard, but the car can pick up up if it has knock sensors.

If an engine calls for 91+ octane, it will need it. But if a car calls for 87 and you "treat" it with a higher octane, you are likely not very intelligent!

Now as for milage. Of course it will be the same. On the highway your not stressing the engine, so it probably was not experiencing much, if any, detonation. I would expect broader results if done in a city with more aggressive driving.

23 mpg at 80 mph sounds about right. I drove the cabrio to CT doing about 5 over the posted limit and got 29 mpg. I also ran premium.

If you're just cruising down the highway on a moderate to cool day you don't need the octane. Stop and go traffic or climbing hills on a HOT day is where you need it. MB said 91 required because they didn't want to risk the liability. Old MBs had a switch in the EZL ignition for different octanes.