Dave,
My 124 also does much better then my 123. It shows that there is clearly an improvement in the OM603 design because usually you don't expect an engine with the same displacement but an extra cylinder to be more fuel efficent due to frictional losses from the extra cylinder. My mileage figures are consistant with yours except generally 1-2 MPG lower (California fuel I guess). City driving is definitely lower but I chalk that up to lugging 2 tons of wagon up and down all the hills here. I can just squeek out 400 miles range on a full tank of highway driving in the 124. The 123 will get 24/25 MPG highway if I'm not climbing Interstate 80 and keep the speed down. Speeds over 60-65 cost me 1-2MPG, the 123 isn't the most aerodynamic design in the world.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

Gil,

If you are using a 205/70-14 in place of the 195/70-14 you should make a math correction on mileage to account for the larger outside diameter of the 205/70-14. Assuming they are of the same brand and tire type, this difference could account for speedometer and odometer errors, on the low side, of up to 5 to 10%. From brand to brand, if you check the tire outside diameter dimensions at Tire Rack, you will see pretty significant differences between brands, for the same "size" listing. So a change from one brand to another may give you a calculated mileage change, but you need to make sure you account for the actual tire diameter. A better pickup feeling also indicates a smaller tire as this gives you a slightly different final drive ratio.

While I am sure the later Diesel engines had some fuel efficiency enhancements built in, I am much surer the drag coefficient of the W124 car (around .35 at its introduction) is far superior to the W123 (probably around .45 or higher). This will account for a very substantial mileage benefit for the W124, as well as a higher top end.

Hope this helps with the issue. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim,

Thanks for confirming my suspicions that the size of tires from different brands, although they are "listed" at the same size, do vary. I have definitely noticed better pickup and fuel economy when I swapped out my Yoko Avid H4s to the Michelin MXV4s. Don't get me wrong, the Avid H4s are great tires at a fantastic price, but I personally don't think they work best with the W123 bodies.

Also, Jim, you're right on about the W124s getting better mpg compared to the W123s. I always thought that the better mpg on the W124 was due entirely to a more efficient engine. He correctly points out that the W124 body is more aerodynamic ( less coefficient of drag) thereby saving diesel.

Happy clickity clattering!

The michelin Energy MXV4 plus is a "green" tire. It will give you better fuel economy and longer tread life than most other tires.

That is why they call it the "Energy" MXV4.

I have these tires on my VW TDI and they are great. They are quiet and are the best tires I have ever had.

This is a quote from the michelin web site...


" Creating the most obsessively engineered tires in the world is the aim of every engineer at Michelin."


Obsessively engineered, hmmmmm....?

Sounds like a certain car company that we all know.

Well, I haven't switched tires during the last several tankfuls, and my 300TD just got 20 mpg, compared with about 25 the tank before. I think these cars are very sensitive to differing driving conditions and temperatures, not to mention different fuels.

'87 300 SDL W126 Turbo

I record every fuel purchase in a three-ring binder I keep in the car (hey, I'm German, ok?!) and I check mileage every 5K, so that way I get a good all-around average, not just City or Highway. I have run Shell Rotella T 15W-40 since day one, in all seasons. Here in MI the four seasons are known as: 'Almost Winter', 'Winter', 'Still Winter', and 'Road Construction'. You get the idea.

It's always been between 29 and 30 MPG, never varies.

I went to fueleconomy.gov as suggested earlier in this thread and was I surprised! They put my Benz at 22 MPG! What fools they be. I guess I shouldn't be too surprised though, should I? We are talking about the Federal Government here, aren't we.


Gil,

You're absolutely right about that Global Warning crap. You can prove any weather or climate trend you want if you only look at a certain time period. You need to step back and look at the big picture. That's where reality lies. They give a much lower MPG rating for my car than is the truth. That way they can justify their false claims about Global Warning. Our tax dollars hard at work!

Medical Dave,

I'm just as ana... ummm, German as you and I track every tank in an Excel spreadsheet, which computes the average (per year) as well. Handy stuff to have around so you can tell if something caused a sharp drop in MPG for whatever reason.

On a side note, since you live in a cold area, why don't you use synthetic oil? It makes a HUGE difference in cold starting ability and also lubes your engine during the first couple minutes of operation, where the 15W-50 dino is basically molasses in the sump. You can extend the drain intervals to offest the cost. I use Delvac-1 and change at 10k (have oil analysis to back that up). Rotella 5W-40 Synthetic is ~$13/gallon at Wal-Mart, it's not the best stuff but would be better than the dino Rotella...




Regards,

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

gsxr,

I was a trucker before I got into medicine (logical transition, right?!) and did a study years ago on engine oils. Conclusion was that Shell Rotella T 15W-40 is the flat-out best stuff out there, period, end-of-discussion, thank you, goodbye!

Seriously, my study did not include synthetics, that's all. I guess I'm just an old fashioned sort of guy, what can I say? That, plus I've still got a drum and a half of Rotella T sitting in my garage.

Someday I'll probably do another study and just might switch to synthetics. In the meantime I'll stick with the tried and true (and paid-for!). Ha!

Interesting! There have been other threads discussing this, and Shell Rotella is consistently at the bottom of the ratings, with Delvac-1300 and Delo 400 being the top dino diesel 15W-40 oils. Hmmm. But yeah, having a drum in your garage is a great reason to stick with Rotella for a while!

As for synthetics, only 2 are officially approved by Mercedes: Mobil-1 15W-50 and 0W-40. Delvac-1 is generally regarded as THE best diesel synthetic available (along with Amsoil & RedLine). The Shell Rotella synthetic is a psuedo-synthetic, a hydrocracked dino base or something like that.

Regards,

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

gsxr and Medical Dave:

Thanks for the tips. I always wondered if there were people out there who ran spread sheets and flow charts on their gas mileage. You guys ever consider, uh, getting a hobby?

Seriously, though, I'm glad to reap the benefits of your painstakingly researched conclusions.

As far as the tire debade goes, well, we aren't talking about an enormous difference in tire size when switching from a 195 to a 205, but I beg to differ that handling is unaffected or made worse. There is definitely an improvement when switching to a slightly wider tire, not to mention variables in rubber compounds, tread patterns, etc.

My brother and I used to autocross a 74 Porsche 914 2.0, along with several people with others like it in the club. Since we ran in the stock class, we had to use either the factory Fuchs alloys ($$$) or the stock VW style steel wheels. The car didn't have the optional alloys, so we used the original steel set.

One thing nobody did was stick with the stock tire size, regardless of brand. The practice of bumping up to a wider and slightly shorter tire was (and is) de riguer for autocrosses, and most certainly does not worsen the handling by causing too much sidewall flex. The shorter stance of those tires gave better acceleration and the wider footprint increased surface area and thereby gave the car better traction. Sidewall flex would have been worse with the taller tire because of a higher center of gravity, and the skinny footprints would've sacrificed road holding. We weren't too concerned with gas mileage, however.




Gil


PS: as far as swapping wheels on the 123 goes IMOHO, putting later style wheels on an older Benz just screams "wannabe" to me. Even aftermarket wheels look so hopelessly....
...tacky?
I just couldn't do it, even if I had the extra cash.

Yeah, I have never seen any non-stock wheels on a 123 that looked good, IMO. Some were tolerable (the BBS-style honeycombs weren't bad) but most just looked wrong. The 124, on the other hand, responds very well to newer OE or aftermarket wheels. The W202 Sport wheels on my one 124 make it look 10 years newer! All highly subjective, of course. :p

On the tires, most folks go one or two sizes wider but keep the same tall aspect ratio - killing any possible performance increase. If you reduce the aspect ratio at the same time, you can pick up a smidge of handling as long as you're only going up 10-20mm in section width. I could see putting a 205/65 in place of a 195/70 stock tire. But trying a 225/60 or 235/55 would just be laughable - on the stock wheel width. The wheel would swim around so much inside the tire, the handling would be interesting to watch at an autox. I had 235/60's on a 7-inch wheel on my 70 Impala, and I could push the car side to side and watch the car+wheels swim on the tire! It looked good, though, and the Impala wasn't exactly a great handling car - even with Polygraphite bushings and massive sway bars (no matter what wheels/tires it had).

Overall I still recommend mounting stock tire sizes on stock wheels, unless you have some very special reason for doing otherwise.


Regards,

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

I thought I was the only one that remembers the 70's scientific consensus warning about the coming ICE AGE because of industrial pollution! It has been mighty cold recently.

__________________
'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.

My 81 300D with unknown miles, it's on the 3rd speedometer, got 25.5 mpg a couple months ago. I changed air filters and mileage jumped to 26.5 mpg for a couple tanks. I plugged the EGR vacuum inlet hose because it seemed to smoke to much during a dead start and mileage has steadily increased to 28.4 mpg. Have you checked the EGR valve? There was no other work done on the engine besides what was mentioned above.

Hi Guys and Ladys
For the third time in the row same road 180 Miles hygway full tank tothe rim i had 37.5 m/g with 60m/h all the way
I now sound incredible ,but i ceck the milage twice against 1 mile mark.
In the town i get for 2 mile driving back and forth around 25 m/g .I have the car from november and i do not had the chance to drive et on summer
I will have to mention i am a control freak for milege because i came from a country where the gasoline or diesel does not grow in the trees like we had here until cuplle monts ago.
The only think i did i ceck the timing and the valve play , run diesel purge 2 times and i wait for the spring to ceck the breaks
I have a book in the car full with every info or change in diesel milage The car is a 300 cd 1985 purchased from ebay whith my eyes closed and i think to change on vegie or partial
I forgat to mention every tank full i ad 8 ounze of my special oil to lift up the cetanes

Here in lovely COLD Wisconsin I have been getting 23-24mpg consistantly with Rotella T Syn. Most of my driving is my commute on the Interstate at about 70-75mph. The odometer was rebuilt by Continental Imports and checks out.

I thought it might get better after some diesel purge, but no...

I hope it picks up in the summer, if we ever get to summer.

__________________
John

1995 E320 - 115kmi+ Smoke Silver/Cream (Wife's Wagon)
1989 260E - 195kmi+ Black/Grey (My Panther)
1984 300D - 242kmi+ Black/Palomino (Retired)