Just got back from Key West - PeachParts Mercedes-Benz Forum

CHAPP · #1 11-24-2002, 06:43 AM

Just got back from a 3000 mile trip to Key West. Car ran great, and diesel was cheap some places on I-95. Ga. had fuel from $1.16-1.25 and southern Va. had it for $1.21-1.30. N.C. and S.C. were a little higher. Fl. was the highest from $1.40 on Rt. 301 to $1.80 at Key West.

I got 23-24 MPG on 75-85 MPH driving on the interstate. I checked everything out before I left...timing, brakes, new tires, diff., air filter. I had the head overhauled & valves, also the injectors. I replaced the turbo with a factory rebuilt. I had the valves adjusted and a leakdown test showed everything was tight. At 80 MPH my GPS says I am going 81.9 MPH and I guess that makes a little difference. I was hoping to get better mileage, am I asking too much for a car with 314K on it?....70K ago I was getting 27-28 MPG....any ideas?

rickjordan · #2 11-24-2002, 10:07 AM

This past summer we drove to Walt Disney World in our TD. Everything is original on the engine, we averaged 70 mph, A/C on and we avereaged 27-28 mpg. Maybe with some more miles on the engine, the head will be "broken in". There aren't too many cars that have over 300K and can do a trip like you did.

JimSmith · #3 11-24-2002, 10:10 AM

CHAPP,

When you got the higher mileage, were you driving at 80 mph? At those speeds most of the work the engine is doing is pushing the air out of the way for the car to move. The resistance goes up by the cube of the speed increase, meaning at 80 mph it takes 8 times the power from the engine to push that air out of the way than at 40 mph (twice the speed means 8 times the load).

I would think you got pretty good mileage. The W123 is a pretty boxy body, and has a drag coefficient of nearer .4 than .3 that is the standard for newer cars, and results in much higher highway speed mileage. Good luck, and thanks for the road report! Jim

Zoonhollis · #4 11-24-2002, 02:29 PM

Jim is right, but I think Chapp's car is a W126, which is only slightly less boxy than the W123...and heavier.

psfred · #5 11-24-2002, 02:50 PM

Tires, brakes, alignment, headwind?

24 is OK, but you should be able to get 27-29. Old tires, worn shocks, worn track rod bushings, and so forth can reduce milage that much by causing drag.

Peter

psfred · #6 11-24-2002, 11:11 PM

My 300D get 34-36 if I can stay at 65. 30 is more like it when I have to run 75-80.

The 280 SE is worse -- I suspect it gets more like 20 at 65 constant speed, but I imagine the milage drops dramatically going faster. Believe me, THAT beast has drag to spare, what with a huge vertical grille, stacked headlights and high fenders up front....

Peter

CHAPP · #7 11-25-2002, 12:55 AM

Thanks for the replies.... I had new tires (double checked the air) and alignment and now I want to test my tubo boost (how?), but I hear the whine. Maybe I am asking for to much...but I was doing about 80 MPH when I got 27-28 MPG before the work. I had 3K on the head before the trip. My old turbo whined a lot louder at highway speeds, and maybe the new one is not adding enough boost. Thanks for any ideas you might have.

Diesel-Lover · #8 11-25-2002, 11:33 AM

Its a drag man exponential that is robbin ya of the high mpgs. Slow er down within limits and
you will get more mpg and more life as well!

Office homest Im still above the CAFE 22MPG!

Happy Trails

jobah · #9 11-25-2002, 12:11 PM

Key west brings back good memories. I made the trip from Chicago in my "old" 190 two times, once at about 120kmi and once at about 140kmi. Many told me that the car was too old to make it and that it was too much to drive it that far.

One trip was with four people, the other with five people. The car averaged a little over 73 the first time and close to 78 the second time. It never did less than 36 mpg.

And with the "too old" comments, I would still drive the old lady to key west today with over twice the mileage!

psfred · #10 11-25-2002, 08:05 PM

Chapp:

Check your odometer, it's due to start "loosing" milage. The drive gear starts to slip when they get some milage and/or age on them, leading you to think you are getting poor milage. I've repaired three so far....

Peter

CHAPP · #11 11-26-2002, 05:00 AM

Well I was doing 80 when I checked it last and got 27 MPG...so I expect the same now.
Psfred... I like the odometer idea and will check (GPS) the miles on a 50 mile trip...going to have the tubo boost checked. I know the speedometer is 1.9 MPH slow at 80.

Ockman · #12 11-26-2002, 05:30 AM

Diesel fuel is winterized during the winter months and contains less "energy" than untreated diesel fuel. Many on this forum can get technical about, but I won't. If the last time you got 28mpg was during the summer, that may be another reason for reduced mileage among the many already posted.

barkford · #13 11-26-2002, 09:21 PM

CHAPP - I'm amazed your Celebrity is still alive. I wanted to drive my 2.5CL into a brick wall - engine rebuild twice.
btw- my 98 e300 does 600 hiway miles on a tank, 80+- mph

CHAPP · #14 11-27-2002, 12:24 AM

Both trips were in the winter & I use performance additive. My GPS says that my odometer is .1 of a mile short every 20 miles or 1 mile every 200. I just bought a K & N air filter and will change that tommorrow. Mileage was much better at 65-70 MPH, but this car loves to run. When I ran heavy equipment...the best running machines were the one's that got run the hardest...diesels like to be run.

The Celebrity's 2.5L engine is still strong but I am on the second transmission. I am the second owner and got it at 30K from a little old lady (really) that had it serviced once a month at the Chevy dealer...with records. It makes a good snow/ice car and has been a good car for me for 6 years.