OM617.952 fuel economy

[MBeige]

I turned back my ALDA to original spec and got 22.55MPG. With 1 full turn CCW I got 23MPG (lowest), sometimes 24, sometimes 25. I wonder how my turbodiesel fares with your turbodiesel (W123 only) in terms of fuel economy. Any other things I could do to increase fuel mileage?

Best I could do was 27MPG. I've done Diesel Purge alongside changing fuel filters, both pre and main, but didn't use up an entire can. Maybe 75% of it. Should I pour that Diesel Purge into a near empty tank and let it run until the "R" light goes on?

Will adjusting the turbo wastegate increase fuel economy? I believe I have the Garrett type. Also does the type of turbocharger affect fuel economy? Others have KKK but I heard perform differently on both city and highway.

[Hit Man X]

Drive a bit slower on the freeway if you drive 75-80mph currently, drag goes up in an exponential form as speed increases.

Make certain tire pressure is proper.

No excessive weight in the vehicle... i.e. empty trunk, no junk in it, etc.

Don't have it full throttle often.



Basically be sensible and aware.

[BruceMcC]

My mpg improved by 4 mpg from installing an an offset key on the valve timing gear and adjusting the IP timing to compensate for chain stretch. IP timing is a bit messy but not too bad. The offset key is an easy job.

I also pop-pressure-matched my injectors at the same time, which makes for a nice idle but I don't believe would improve fuel economy.

Bruce McCreary
'85 300D

[Old300D]

Originally Posted by BruceMcC

My mpg improved by 4 mpg from installing an an offset key on the valve timing gear and adjusting the IP timing to compensate for chain stretch. IP timing is a bit messy but not too bad. The offset key is an easy job.

I also pop-pressure-matched my injectors at the same time, which makes for a nice idle but I don't believe would improve fuel economy.

Bruce McCreary
'85 300D

If you can equalize the fuel delivery in the cylinders, you will improve engine efficiency at all rpms. It's a slight improvement, but it sounds good in theory.

[MBeige]

Originally Posted by Hit Man X

Drive a bit slower on the freeway if you drive 75-80mph currently, drag goes up in an exponential form as speed increases.

Make certain tire pressure is proper.

No excessive weight in the vehicle... i.e. empty trunk, no junk in it, etc.

Don't have it full throttle often.



Basically be sensible and aware.

Do you know what the drag coefficient is for the W123? Thanks, I'll try slowing down. I adjusted my ALDA back to its "tweaked" configuration, hopefully this will yield better fuel economy.

I'm sure the junk in my trunk will also have to leave should I yearn for better mileage, but I just noticed the difference between original spec ALDA and its tweaked spec -- the original spec gave less miles per gallon.

Also noticed, starting is much smoother with the tweaked ALDA.

[t walgamuth]

the mileage stated is similar to what i have experienced with the 300 turbo. i have had five. .. driving 75 on highway. weight wont affect highway mileage but can affect city but probably not measurably, unless it is really a lot of weuight, in my opinion.

[Hit Man X]

Originally Posted by MBeige

Do you know what the drag coefficient is for the W123? Thanks, I'll try slowing down. I adjusted my ALDA back to its "tweaked" configuration, hopefully this will yield better fuel economy.

I'm sure the junk in my trunk will also have to leave should I yearn for better mileage, but I just noticed the difference between original spec ALDA and its tweaked spec -- the original spec gave less miles per gallon.

Also noticed, starting is much smoother with the tweaked ALDA.

Nope sure don't. Lower RPMs make the motor run more in the torque band, a few SD owners have installed 2.47:1 diffs and picked up 3-5mpg. Drops RPMs a good deal from the 3.08:1 and 2.88:1 diffs some cars have. Since I dwell mainly on the freeway, it's no big loss to me.

I drive my SD 60-70mph on the freeway, economy is constantly low 28s to low 30 (I keep accurate records of my milage on each fillup)... it's probably 75% highway. I do also have a 2.88:1 diff currently. I use fuel from a high turn-over location too.

[MBeige]

Thanks, I don't think a differential swap is practical (financially) any time soon. I too keep records of my fuel economy on my receipts. My 300D runs 80mph at roughly 3800rpm. 75mph at roughly 3500rpm. So I'm guessing 70mph will run at 3250rpm and 65mph around 3000rpm.

Won't a drop in RPM result in a loss of power? Here goes the balance between power and fuel economy...

Thanks again

[MBeige]

Originally Posted by t walgamuth

the mileage stated is similar to what i have experienced with the 300 turbo. i have had five. .. driving 75 on highway. weight wont affect highway mileage but can affect city but probably not measurably, unless it is really a lot of weuight, in my opinion.

I would think the same about weight and city driving. I once took a trip to Zzyzx road on the way to Vegas from CA. One way was 225 miles and I had two friends, a trunkfull of bags, and windows open (no AC ). Total distance was 450 miles. I averaged 24mpg with bursts of 115mph. My first time to travel 4 hours straight. Arrived back home the next day with dirty wheels, but the car was begging for more. My oil leaks also stopped.

Even in city driving, my mileage is roughly 23-25 mpg. I guess highway and city driving make no difference for my car?

[vwbuge]

My car has the ALDA turned up and a boost controller installed. Boost is up to 13.5 psi. It seems no matter how I drive I get 22mpg.
I have a different rear ratio than most of you though.

[WANT '71 280SEL]

When I had my '79 SD, I got 25 mpg, and that was tops. I think your numbers are pretty normal. Though these cars were built for economy, 20mpg back then was miraculous. If you want better economy, step up to a 603. I get 26mpg on the highway, but I still need to have my IP timed and injectors tested.

Thanks
David

[Hit Man X]

Originally Posted by MBeige

Thanks, I don't think a differential swap is practical (financially) any time soon. I too keep records of my fuel economy on my receipts. My 300D runs 80mph at roughly 3800rpm. 75mph at roughly 3500rpm. So I'm guessing 70mph will run at 3250rpm and 65mph around 3000rpm.

Won't a drop in RPM result in a loss of power? Here goes the balance between power and fuel economy...

Thanks again

Torque drops as RPMs rise, you want to drive in the torque band.

I have a dyno plot that someone ran a 300D a while back... it was around 85rwhp/155rwtq.

It's slower at 65-70 than 80mph, but give it a shot for one tank of fuel. If it works great. If not, happy speeding. But not only are you running at higher RPMs drag is against you the fast you go, causing you to use many times more fuel than you would at slower speeds.

[Cateaux]

Originally Posted by MBeige

Thanks, I don't think a differential swap is practical (financially) any time soon. I too keep records of my fuel economy on my receipts. My 300D runs 80mph at roughly 3800rpm. 75mph at roughly 3500rpm. So I'm guessing 70mph will run at 3250rpm and 65mph around 3000rpm.

Sounds like you have a 3.07 (3.08?) differential.

Originally Posted by MBeige

Won't a drop in RPM result in a loss of power? Here goes the balance between power and fuel economy...

The OM617 turbo reaches its peak torque at 2400rpms. Though the torque band is nice and flat, the further above 2400rpms the engine spins the less torque it produces. It reaches maximum horsepower around 4300rpms, I think, but torque is what you need to push past wind resistance. It would be nice if I could find a way to cram in a Gear Vendors overdrive unit with a .69:1 ratio. This would drop engine speed to about 2500rpms at 70mph, which should result in incredible highway fuel mileage, top torque at cruising speed, and no loss in city performance.

[boneheaddoctor]

My W116 is supposed to have a 3.07 diff per its stamping...yet it turns far more rpms at 80 mph than my W123 that also has a 3.07 diff....about 800 rpms more. Why nobody can explain?

But my Heavier higher reving W116 gets 25 MPG very regularly...where my lighter lower reving W123 gets 20-22 mpg driving the very same route under identical circumstances........

[Hit Man X]

Originally Posted by boneheaddoctor

My W116 is supposed to have a 3.07 diff per its stamping...yet it turns far more rpms at 80 mph than my W123 that also has a 3.07 diff....about 800 rpms more. Why nobody can explain?

But my Heavier higher reving W116 gets 25 MPG very regularly...where my lighter lower reving W123 gets 20-22 mpg driving the very same route under identical circumstances........

Does the converter stall any higher? That could account for the higher RPM as it doesn't lockup.

Do all 722 trans have a 1:1 4th gear? I believe that 116 has a four bolt version so maybe the gearing is a tad different? Such as a 1.41:1 final gear in the trans?