Diesel W123 MPG. Lets get real! Chime in with your MPG
 

OK. So we see these on Craigs and on Ebay with people claiming outrageous MPG.
I know the VW diesels can actually get 50MPG.
But, I've had half a dozen of these.
My 81' W123. I usually got around 24. The best I ever got on an all highway trip with over inflated tires I got 33MPG.
On my 95 W124the best I ever got was 37MPG on an all highway trip on a very cold night, other than that mid 20s.
I'm looking at a W123 Diesel wagon with a 4 spd. He claims 40-45 MPG.
I know that love can make a man do and say things that aren't quite true.

What MPG do you get?
Do you do anything special to get it? (Eco mods, synth oil/ trans fluid, air dams, smooth caps etc..)

Thats pretty good for an automatic. The problem with these threads is everyone posts their one time best tank under ideal conditions. The long term average over multiple tanks (which most people don't calculate) is far more important.

W123 300D, OM617.912, automatic - 25mpg average mixed city/highway on B99. Would be a bit higher on D2.

Last January when I drove across the country in my 1978 300D, I got above 32mpg on the freeway. My best mileage was after a fill-up at Capitol Oil in Topeka. I made it all the way to eastern Ohio. There I made the mistake of getting diesel from a mom and pop filling station and I think it was either gelled or had water or algae in it. My fuel economy went down the toilet after that.

Once I changed my injectors to newly reman'd Bosch units from Pelican, my daily commuting fuel economy went up. Before the injector swap it was low 20's in the city. Afterwards, it was mid-high 20's depending upon traffic. There were a few places there in Hudson and Bergen counties that I had to drop the car in low and floor it to merge onto route 1-9. Daily driving around there I'd get about 26-28mpg average but I had to dilligently watch my tire pressure and ensure that I go good fuel from one of the truck stops which had a high volume.

Phil Forrest

1976 300D automatic transmission (no turbo)!!!
 

1976 300D automatic transmission (no turbo)!!!

This car is totally Stock.
Up to 70 MPH, my daughter gets a solid 21 city - 25 highway MPG, even when treating it like a sports car. :D

Above 70 MPH the MPG seems to fall, roughly 1.65 MPG per 5 MPH.

Example: MPG 18 when driving 90 MPH, and the engine is NOT happy. :eek:

.

I don't have a 123 but my 87 w124 has never gotten less than 30mpg with a best of 34. The 30mpg was a tank full of 85 to 90mph drives though my 70mile one way commute. The 34 was doing 55 to 65mph depending on speed limit.

I recently started to record the mileage.

https://www.fuelly.com/driver/zorecati/300d?fu=5523902

One of these days I should really try driving that slowly for a whole tank, I've heard great things about it. Unfortunately 55-65 around here relegates you to the slow lane where the pavement is full of potholes from heavy truck traffic. Those same trucks will also be tailgating and passing you on the left.

+1 on Fuelly. Surprisingly few 300d drivers are using it. Its an excellent tool to track mileage, cost per mile and I also use it for oil change intervals.
Mercedes-Benz 300D MPG Reports | Fuelly

Here's my mileage on a recent coast-to-coast trip in October (San Diego to North Carolina) This is my 107 with a 617.952 engine, 722.3x transmission and 2.47 rear end. The 107 has about a 200# weight advantage, but with luggage and 2 passengers, some of that was likely countered.

http://www.peachparts.com/shopforum/...trip-stats.jpg

Note that my odometer reads 10% high so the mileage numbers are raw while all the other numbers have the correction factor built in.

Wind, altitude, braking, speed all have a huge impact on mileage.
The 2.47 rear end probably helps a lot- 2600 turns at 70mph. My "normal" everyday around town is usually around 29.

Would you please ask him to join the forum and post his methods as to how he gets this fuel mileage? I would love to get 40-45mpg in my '85 wagon. Heck, I'd be happy to get 30-35mpg.

It's been a while since I thought it was necessary to calculate my fuel economy. When I did I was averaging 23-24mpg all around, city and highway combined.
Now I just look at it like this: when I am putting fuel in my tank, I multiply the # of gallons by 22 and that's how far I figure I can go on that particular fill up (almost never fill all the way up, usually put in $20-$30 for around town puttering). Then again, I seldom pay much attention to the (trip) odometer and almost never reset it when I put fuel in.

My old DD was a 1985 300D Turbo, and was mostly stock. It achieved 25 MPG +/- 2 MPG consistently, and that was running either #2, WVO, or a blend. It did not matter.

My current DD is a 1983 240D with a 300D NA (non-turbo) and 5 speed Getrag 717.400, but it has a higher ratio diff. After some recalculations of my initial testing, it achieved 27 MPG consistently before mods. With mods, e.g., power steering delete, et cet, it achieves 30 -31 MPG on #2, WVO, or a blend. It does not matter. I am thinking a 2:88 will help out a little also since most of my driving is highway miles.

I know a gallon of WVO has less BTUs than a gallon of #2, but I have not seen any difference. Even a blend with RUG, I really do not see a difference and RUG has the least amount of BTUs than WVO or #2.

Once I get the car back from the paint guy, and re-install the water injection and complete deleting the mechancial water pump and vacuum pump, et cet., I will test the MPGs. My overall goal is 35 MPG, however not sure that is ultimately doable unless I shed some weight. Off my gut as well. LOL.

I would say that the folks who are hitting 40+ MPG are either mistaken, misleading, or they drive extremely frugal. There are contests where folks compete in regular cars and they hit some incredibly high numbers. However, those driving habits would be tough to keep on a daily basis, e.g., always drifting downhill, turning off the car while drifting, driving no more than 55 MPH, et cet.

A VW hit 80+ MPG New world record: 1,626 miles on one tank of gas - CSMonitor.com

Rt to Florida
 

Car is 1983 300CD. Fresh oil change with 15W-40 AMSOIL. Fresh valve adjustment. Fresh air filter and fuel filters.

Starting miles: 290788. Ending miles: 293341
Total miles driven this trip: 2553

Trip route:
Leg 1: Near Richmond VA to Tampa, FL via U.S. 1 to U.S. 301 (no interstate hwys)

Leg 2: Tampa to Ft. Lauderdale. No interstate hwys
Car parked in Ft. Lauderdale for 5 days.

Leg 3: Ft Lauderdale to Charleston, SC. No interstate.

Leg 4: Charleston SC. to Home. Interstates all the way at speed limit (65 to 70 mph).

Air conditioning most of the way, cruise control used where feasible. Ran speed limit. Did not avoid small towns.

Fueled 10 times (kept at 1/2 full).

Threw out the high mileage and the low mileage and averaging the rest provided a real world mileage of 29.456.

'83 300D, stock except for a four speed swap from a '77 240D, tires aired up to 36-40, and driven hard enough that I wore out my last set of tires in 17,000 miles. My last fill up came out to a bit over 26 mpg. I typically get 24-25, but can hit 30 on long highway trips.

My 1982 300TD wagon got a consistent 24-25MPG with mixed driving (60% HWY, 40% CTY), and topped at 31MPG on a trip from VA to RI, driving between 55 and 65 MPH. The 1987 300TD wagon was 80% HWY, 65-70MPH, and returned between 28 and 30MPG.

I emphatically disagree. Curbsiding makes vendors do and say things that aren't true.

If the car isn't too far away, and taking the time to go see it doesn't take precious minutes away from such vital functions as, say, nosehair trimming or teaching the dog to vacuum, by all means go.

If it involves major time and/or travel... don't say you weren't warned if you get there and a lot of other claims are fanciful too, like it has a floor, never seen salt, idles like a Honda, blah, blah blah.

Stupid claims in ads aren't part of the game. They are asshat alerts.

Miguel, it is nice to hear from you again (even though you are stuck in Spain). Now back to our regularly scheduled topic- Of all the 123's I have checked, (617 turbo/automatic) the average is around 24-27. I get around 30ish with the 240. This is all with WVO/RUG blend, so D2 may give higher numbers.

Not in this life time. Dropped from a crane "Mythbusters Style" maybe? Not to mention it is a wagon. Wagons get worse mileage by design aerodynamically. The person posting may have Dementia or something. My father has been diagnosed with that disease and it is funny some of the things he says sometimes regarding numbers.


This is a W123 thread... I remember clearly on the one I had. We were driving 600 to 900 miles per week at times (when I owned it). The amount of miles we were driving was part of the reason I sold it. It was just not holding up.

The 85 that I owned always returned 24 to 26 MPG. That was running a mix of B99 and #2. That is also interstate speeds around 75 MPH. I think it got 27 MPG one time? I just figured I calculated it wrong or something.

NOT an economy car to be sure...

Best- 29.4
Worst- 24.7
Average- 26.5

I love my Car Minder app.

OK. So let me get this straight... you have a diesel SL? That's pretty sick. All that stuff about the gear ratio is over my head though. Did you use the original turbo?

Yeah. I've had a half dozen of these cars and I've only seen numbers aproaching these coasting downhill in neutral.
That being said. If you all want to get better mileage the key would be to improve your aerodynamics by making several small mods that will gain you small MPG gains.
The easiest and lease obvious ones are the only ones I would do on a 123.
I've been reading alot about these aero eco-mods. Some of them are pretty over the top. But the best and easiest one I read about was from a guy who get about 30mpg from his volvo wagon: Cover the gaps between the gas tank and the rear bumper under the car. (uncovered it acts like a parachute)
Some other ones are to cover the entire underside of the car with hard plastic panels.
Have you ever looked at the underside of a 1987 300TD wagon.... panels. Block up the grill ( I wouldn't do that). Add little aero flaps in front of your wheels, these direct the airflow under your tires instead of up into yoour wheel wells where they will cause resistance.

Hi everyone!

The best mileage I've ever got out of my 240D was a consistant 36-38mpg, which baffles me because the only time I've achieved those numbers were driving round trip from Albuquerque, NM to Taos, NM. For those unfamiliar with New Mexico geography, Taos is on top of a Mountain. I used to make that drive every morning through blizzards and wind and really nice days too. Naturally, I coasted as much as I could on the way back down, but it just doesn't seem like that should make up for all the fuel burned on the way up.

On the flat, I get about 34mpg if I drive at 65, or about 30 if I'm running 75 to 80.
Cheers!
Chris

I forgot to mention. The 240 is turboed, four speed manual trans, and 3.07 gears. My only aero mod is taking off the side mirrors! :D

What year? Is that turbo and gearing stock?
Hows the pickup on the 240D?

I see 25-27mpg in my 240 4-speed. The wifes 300TD wagon gets about the same when she's driving, and worse whem I'm driving.

Gearing can do huge things to economy though. In my 89 van with an 80 240 motor, I see 27-29mpg very consistently. Its heavier and a worse aerodynamic shape by far, and It blows the doors off both 123s in the family because its got an overdrive 5th gear even though its using effectively the same engine as my DD 240

Search mach4's username, he has a fabulous thread on the conversion of his SL. Worth the read

Hi Chris!

The car is originally a 1983 240D non-turbo with an auto trans. I changed the gearing to a 3.07 diff out of a 300 turbo, which dropped my cruise rpm about 600rpm IIRC, so its turning about 3200rpm at 75mph. I'll re do the math if you would like. I also swapped in the four speed manual trans. I manufacuture an adapter plate that allows puttin a 5 cyl turbo manifold off a 617 on to the 4 cyl 616 which makes the conversion as easy as bolting together lots of junk yard parts, so thats how the turbo got on there! I have pics in my old posts. Since then a different air filter set up is used and I've improved the oil separator. I will post some new pics this weekend after the whole Thanksgiving family drama is over! :D
Cheers
chris

I forgot to mention the pickup is quite good! IP is also um......not stock. :cool:

That is pretty cool right there. I wonder why Mercedes never put a turbo on the 616.

What did you do to it? 617.95 elements?

This is gonna be kinda longwinded!
 

How I modifiy the IP:

The pump mod is dead simple. Take off the back cover of the pump. Once inside look at where the throttle shaft goes through the pump body. There is a tube that the throttle shaft goes through that I call the start/run lockout link. This link at one end engages some other parts that limit the rack travel, the other end links to the governer. How it works is that at cranking speed the rack is allowed to move to its Maximum fuel position for starting. As soon is the engine starts and the governer weights start to come out, this link limits rack travel, and the difference is Huge. The trick is to remove this link so that you can get Full Fuel all the time! Well at least till the governer pulls back due to RPM.

Removing the link is pretty easy. There is a little wedge with an 8mm nut on it that must be removed and of course the snap ring on the far side of the throttle shaft. Slide the throttle shaft out of the body untill you can remove the start/run lockout link, then slide the shaft back in. The little wedge will drive you crazy for a bit, but once everything is back together, you are set.

Stock fuel per squirt on a 240D is about 41.5 cubic mm. Stock fuel on a 617 turbo is about 51.5 cubic mm per squirt. Just this mod with stock pump elements make about 114 cubic mm per squirt! Thats nearly 3 times the fuel with one easy little mod and you don't mess up any of the governer spring balances or anything, and its easy to go back stock if you ever want to.

With this much fuel you absolutely Must have a turbo, or maybe a supercharger. I'm thinking of trying that! Sorry I dont have pics of all this. They were lost when my old computer died, but maybe this weekend I can take some more so you guys can see what the part I'm talking about looks like.

cheers
Chris

I think i need to do a little maintenance on the old girl but right now i am only getting right at 20mpg.

BJ3 i watched your videos and there is one that shows a 4cyl diesel in an astro van, what motor was used in that one? 4bt? the 4bt is not a cheap motor however finding a old Merc motor is not so tough even in you have to part out the donor car....

That's got a 1980 240D 616 in it, turbocharged just like bio240D's car. Though I have not modified the IP yet, so its not putting out the power it should.

I get around 28 Mpg in my 240D with the autotragic. I think the best was 31 the the worst was 22 back when I first got the car with a lot of deferred maintenance needed.

I'm jealous of BIO240D
I know he says that is dead simple, but I would F that up in heartbeat.
I keep my hands out of stuff like that.
Bolt on parts are as far as I go.
Although I wouldn't have a problem getting a part fabricated as I know some machinist who spend all day doing boring stuff and would enjoy making something interesting for a change.

Bio240D,
I also have a buddy who is a diesel mechanic who claims you can add a little pigtail to the turbo which will gain you 3 pounds of boost. Would you need to adjust the IP for that little increase or would it compensate.

Come on why break the habit - gorra keep your post count up!

For the record my OM617 currently does less than 1 mpg!


(0 miles and 0 gallons)

I misposted :).

Hey, our cars get the same mileage!

Come on Stretch! 0/0 is not less than 1. Sheesh!

Yeah, that's undefined! So Stretch's mileage is "undefined"! That's almost as cool as "unauthorized".

Please note I didn't quite say that - I got my less than one figure by starting out with one of the zeros and thinking => "well that's a suitable engineering approximation'!

Undefined!

Unauthorized!

That sounds terrible - like it'll never get better

82 300D, auto. Usually got around 22mpg, saw 28mpg once but that was a rarety going 50-55 the whole way

Im glad to say I get around 20 mpg ,I do alot of stop and go ,I would imagine 25mpg would be doable if I stayed in the slow lane but thats not practical,down here every lane seems to be the fastlane.

83 300d Turbo....automatic..I average 26-27 on a local 50/50 city highway circuit between home and office....on 100% highway (say on a trip from Washington, DC to North Dakota averaging between 70 and 80 mph) I averaged 31 mpg once I got past the Allegany mountains. (mountains do a job on mpg)

ROFL
 

At the moment MPG is horrible.
Weather and road conditions are forcing most driving in second with rare moments in third gear.
Eighteen miles in second gear really sucks LEMONS.
The sub-zero (-16) temperature is below road salt effective temperature range = ice covered roads..
http://www.peachparts.com/shopforum/open-discussion/349586-road-salt-effective-temperature-range.html#post3267405
High (crazy) expressway speed has been 45 MPH for several days, 20 - 30 MPH is average.


http://i21.photobucket.com/albums/b2...ps4e296fbb.jpg

.

Haha.

I can beat that. My 83 300TD gets less than 0 as well, except it has been running several times, but hasn't moved under it's own power. I've moved it about 4 feet forward. So that's...

4 ft = .00076 miles. And since I was pushing it backward... that's -.00076 miles :D

Probably has gone through a little over a gallon in fuel.

So -.00076/1 = -.00076 mpg!:cool:

Where's the like button - oh yeah that's the new thing on BW...

My 1982 240D stock avg 22-23 driving city and some 65 mph highway on good diesel. The 240D speedometer is about 10% off high on these vehicles so reality may be lower 20's.

Any idea how many rpms at 60 with stock rear end? By noise it sounds like +4000 rpm.

These results match my 77 300D (non-turbo). In town I get 21-25. 21-22 when I drive it hard and 23-25 when I drive it like the Grandpa that I am. I drove from Baton Rouge to a Pull-A-Part in Jackson, MS and got 27 by driving 50-55 on cruise control.

I now tend to drive it "like I stole it" all the time. It runs soooo much better when I do that consistently.

a couple of years ago I spent a summer driving a friends 2 w126's; an 85 & an 84, both 300SD's. Lots of miles on both (250k = 84, 500k = 85), so they were well broken in. The 84 would get 26 on the open road (70-80mph) while the 85 got 20-22. Both had new rubber at 36psi (michelins), correct alignment, same level of maintenance, same fuel source (D2 from the same tank), same route (Chicago - Joplin). Three notable differences; wheel/tire diameter (84 had 14", 85 had 15"), turbos came up to full boost differently, rear axle ratios seemed to be different. I preferred the 84 even though it accelerated slower, it just rode better at speed (both had fresh shocks & springs).

1984 & 85 300D, normally 20-22 mpg in mixed city-hwy driving 18 mi one-way commute. Measured 26 mpg on 600 mi trip to San Diego, 65 mph, mostly flat but 1 mountain range and little wind. I use the (calibrated) fuel pumps for volume and Google Maps for distance. Revised EPA rating is 19 mpg hwy, which seems low. I wonder if a Tesla could make the claimed 400 mi LA - SF drive. Probably not if running AC and any head-wind, and would be painful to fall short.

I wonder how many people really know what their mileage is. So many odometer errors and I doubt that most people really understand the wet vs dry pavement odometer errors.
I will see around 5% difference on a windy day trip vs a calm day (round trip) heavy rain, mountains, snow or slush, and of course the dreaded winter diesel will kill many people's high mileage dreams.
How many of you have checked your wet and/or dry odometer readings vs GPS?

I add about a gallon after each run so I get about 2 MPG, not including the start and stop up to the start line. So maybe 3 MPG given that the staging lanes are about another mile or so.

Can anyone top THAT!!??

Dan

I'm kind of embarrassed. I forgot a part of the return road so it's really about 4 MPG. Callin' myself a liar.

Dan