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Old 08-28-2008, 06:16 PM
777funk's Avatar
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Originally Posted by nhdoc View Post
These fuel economy threads are getting to be like oil threads. How many of them do we have to deal with? Here's the facts again, you CANNOT ACCURATELY MEASURE FUEL ECONOMY THE WAY YOU DID IT, PERIOD.

Can we be any clearer than that? You will not consistently get 48 MPG from a 300D so don't think it will happen again. Maybe low 30's, MAYBE if you are lucky.

At some point someone will post that they filled the tank to the brim, drove a mile and it was still full so they conclude their car doesn't burn any fuel and gets infinite MPGs.

Seriously, you just can't accurately measure MPGs by doing small trips and topping off the tank, almost everyone here knows this. Even one full tank is not significant need to do several full tanks and average them to get anything that resembles an accurate measurement.
I think everyone here has said the same thing as you just did. The point has been heard. That's cool and No sweat there...

There weren't any math or major number errors in my measurements (73 miles by map) and 1.53 Gallons at a slope with the filler neck at the highest point. Topped to the brim. But of course this is a 73 mile trip. I do realize this.

The only factor that could have thrown in error, that I can think of, is what PawoSD had stated with the expansion of the fluid. And he has a good point.

But... but... but... if one person can squeak 33 miles per gallon out of a w123 300d powered by a 617, I'll still bet (not realistically, I don't bet and I might loose lol) that a 300d powered by a properly tuned 603 will do closer at least 40MPG with easy driving and staying around 60MPH. The 124/603 combo is typically known for better fuel economy and power than the 123/617.

And slightly advanced timing almost always results in better fuel economy. I don't think anyone would argue that.

Of course take my post with a grain of salt. It's not meant to be salt in a wound to anyone. I know fuel economy is a sensitive issue. It is to me! I'm not meaning to offend anyone here. Great place, Great people, and the point for me is never to start an argument.

But this is a forum and I'm posting what I've tried. I'll of course take a longer sample in the future and of course a best of 3 as in any good experiment.
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Old 08-28-2008, 07:32 PM
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nobody's offended by this, we're just trying to educate the few people left out there who think they can accurately measure fuel economy the way you did can't be done.

And, no, I don't think you can say you will be able to get 40 MPG out of your 603 consistently by tweaking it and driving 60 MPH unless it is all downhill and with a strong tailwind. It's just not doable.
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Old 08-28-2008, 11:16 PM
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Location: Milford, CT
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Originally Posted by DslBnz View Post
How slow is your commute? With me, I stop about 3 times to work over 15 miles. I accelerate pretty hard (shifting at ~ 4400 rpm minimum, sometimes stretching out to the full 6K), and coming out of corners, I hit it hard too.

I average 28 - 30 mpg, in the SDL. On the highway, it's about the same. I do have a straight pipe, though.

I averaged about 21 mpg in my old 1990 300SE. Again, highway mileage was equivalent.
My car doesn't have the Ferrari engine option so it only goes up to 4,800 or so. Not that I would want to regularly thrash a 20+ year old motor like that.

Lets see I take a left out of my street, since its a hill for the first few hundred feet I actualy just coast down it, than I make a left and accelerate to 30-40 on Pond Point since the engine is cold, no more than 2k. For about 1k feet or so. Take a left on New Haven Ave for about 200ft, again 2k. Than a quick right onto Old Gate for about a mile. All these are 40mph or less streets, never more than 2k. Than I take a quick left onto Woodmont, and jump on I95 south at Exit 40. Since the engine is warm usualy I bring it up to 2.5k, or 3k. But still everything is cold so no thrashing. I get up to 55-60, and cruise their for about 2-3 miles until exit 35. Than take a quick right and left. Opal street is the second or third right 1/5 of a mile down. Since Opal is so short and the job site is 200ft down on it, I usualy just take my foot off the throttle and let it coast down Opal.

Than I usualy add about 10-20 miles of around town running during the day, trying to keep it well below 3k. Every few days are so when its nice and warm I'll run to the stops in a few gears to blow the exhuast out.

I have been keeping track of my mileage since I bought my car in 2004; over the past now 5 years and just about 40k miles, its been between 21-23, with probably about a 22.5 average. On long trips I'll see 25-27, but those are meaningless one tank flukes.

My old broker who bought her SDL almost new drives like you, she uses the throttle as an on off switch, every single shift is over 4k. Her car when it was pretty much new only got about 20-21 seeing this type of around town service, still does, she gets about 400-425 out of a tank.

Your car must have a special engine, or the muffler sucks a lot of power.
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