Real-World 617.950 Fuel Economy - 1,000 Miles a Week: - PeachParts Mercedes-Benz Forum

Doktor Bert · #1 09-29-2012, 10:04 AM

I have been driving this 1978 300SD for almost 20 years now. I think I drive it harder, on a constant basis, than most of you do. Forum member 'Hammerwerfer' has ridden in the car and will attest to it's incredible acceleration and how hard I push the car on a regular basis.

The 300SD has evolved to some extent, after the rebuild/upgrade of the engine and transmission back in 2004, but it is, for the most part, a very basic engine with nothing more than increased boost pressure (14.7 psi @ WOT and roughly 10-11 psi @ Cruise) increased primary fuel pressure, upgraded compressor wheel, ported/polished head, 3.0mm of shims under the ALDA (Atmosphärische Lade-Druck Anpassun (for MBZ trivia fans) Injectors set to max discharge pressures and advanced camshaft and IP timing. I am still running the direct-drive 722.120 transmission, the original 3.07 (awful) axle and the factory optional 205/70R14 tires.

I have several videos posted that show the boost gauge going to 10 psi at about 2,000 rpm with only about 1/2 throttle. I have several You Tube videos that show the cars 0-60 and 60-105 mph acceleration, as well as the tire-screeching 1-2 shift.

For 11 years, I commuted 110 miles a day from my home to the police department where I worked. I drove the 116 frequently, because it would net between 22 and 28 mpg, depending on how it was driven and whether or not you were running the A/C. After I retired last year, I took the 116 with us to So Cal.

Although I live in Palm Springs during the week, the past two weeks have seen me home every night at our home in the High Desert, a 214 mile daily commute. To me, the drive isn't at all bad, so I really don't mind it. I guess after my recent trip to Florida and back, nothing seems that far to me anymore!

Over the past 2 weeks, I have been watching my fuel economy really closely. I have discovered a number of things about the old 116 I thought I would share with all of you.

In all the years I drove the car, the low fuel light (a red triangle on the 116) never came on. I thought it was broken. In every instance, when the fuel gauge read empty, I could fill the tank with 16 gallons of fuel. Recently, I ran the car much lower on fuel than I had ever done before and the red triangle lit up. I set my trip meter and drove the car until it ran out of fuel.

What I discovered was the car would go 110-115 miles from the time the low fuel light came on until it literally started running out of fuel. Filling the car from this dead-empty condition took a full 21 gallons, which means there is 5 gallons left when the red light comes on.

My morning commute begins about 4:15am PST and my speeds range between 70-80 on I-215 all the way to the I-15/I-10 interchange. Once I get past San Bernardino, I frequently run between 100-115 mph, when my side of the freeway has minimal traffic.

Between last week and this week, with a little over 2,000 miles driven, and running the A/C on every return trip (no A/C in the morning) the 116 has yielded an average of 25.75 mpg, with the best numbers near 30 mpg (28.7) and the worst near 23 mpg. Ironically, being stuck in stop-n-go traffic hurts my economy more than higher speeds do!!!

I am going about 525 miles on a full (20 gallon) tank, but I prefer to fill up at the 'E' which takes about 16 gallons, which gives me about 425 miles to a tank of fuel.

As far as maintenance goes, I am a true minimalist. The first secondary fuel filter went 45,000 miles before I changed it. I usually change the primary filter at every oil change, but I don't change oil very regularly either.

Ideally, I like to change the oil at 5,000 to 10,000 mile intervals. I have used a lot of different petroleum based oils, to include Chevron Delo 400 15/40, Mobil's Delvac 15/40, Shell's Rotella 15/40 and, most recently, Valvoline's 15/40 Diesel Engine Oil. I get the most consistent oil pressures with the Valvoline.

I have run the engine about 15,000 on one oil change, partly due to a maniacal schedule and sheer laziness, although I did throw in a new OX-78D filter about mid-way through the cycle. I try to adjust valves at about the 15,000 to 20,000 mile mark, although the last 2 times they were still within the .006" and .016" setting where I like to keep them.

I serviced the 722.120 after about 50,000 miles, and I only. ever use Ford 'F' Type fluid in these units. I feel the more aggressive frictional properties in the Ford (MC233-F specification, IIRC) fluid makes the bands and clutches last much, much longer. I have been using F-Type in customer rebuilds ever since the early 1990's. There was nothing at all in the pan and the fluid still smelled good at 50,000 miles of use.

I'm not starting a debate on the merits of Dexron vs. F-Type, I am just telling you what I do on this car.

I have used all kinds of things in the fuel, from 2-stroke premix, to MMO, to ATF, Cetane Improver, Lucas Upper Cylinder Lubricant and even 6 months of running on 100% VVO. The engine runs quietest and seems to make the most power on VVO. As far as additives go, it has been tough to really feel a difference, although I can see the presence of the additives in the clear primary filter. I sometimes throw in some 2-stroke premix just to put a little lubricant in the system.

I have been, for quite some time now, planning a 2.47 rear axle swap, but I cannot take the car off the road long enough to work on it. My wife has taken a liking to my 2001 Supercharged Mustang GT, so I find myself driving the 116 again daily.

I have to say I miss being able to wring 155 mph out of a car every now and then.

Interestingly, the Supercharged 4.6 Litre V8, running 7lbs of boost, laid down 27-28 mpg numbers all the way to Florida and back running the A/C 24/7!!!

I would like to be driving a more modern car, perhaps a mid-1990's 300TE, but having a kid in private school and saving up to buy a new house all mean keeping expenses at a minimum, so I keep on driving the ancient W116.

I'm not sure if these ramblings will help anyone, but perhaps the results of my fuel economy over the past two weeks may help to establish a real-world baseline for what the average 617.950 will churn out.

Regards,

Robert

pawoSD · #2 09-29-2012, 10:18 AM

So....the fuel economy?

Doktor Bert · #3 09-29-2012, 10:55 AM

Quote:

Originally Posted by pawoSD

So....the fuel economy?

Had to write a bit and then save, plus refill my coffee cup repeatedly....

Doktor Bert · #4 09-29-2012, 11:11 AM

Photos from my recent 6,300 mile trip in my Supercharged Ford Mustang GT. My average fuel economy over the entire trip was about 27 mpg.

haromaster87 · #5 09-29-2012, 12:47 PM

Wow, that's really impressive. That makes me want to look at W116 SD's! I had a W116 1974 450SE, and man I loved it. However, it got horrible fuel economy. I wanna say it did about 10mpg or so. It was rough. Granted, then engine needed some tuning and probably had some slightly better economy capabilities, but it wouldn't have been that much better.

Oh and I remember the fuel light in my car was quite different. I remember the first time it came on. I was used to driving my moms W210 which seems to have another fuel tank available when the light comes on. On the other hand, my fuel light came on and I was on the side of the road in 10 miles. lol

So you said you did a rebuild of the engine in your car? How extensive was your rebuild? Did you do it yourself? Do you mind me asking the cost, roughly?

Doktor Bert · #6 09-29-2012, 01:29 PM

Quote:

Originally Posted by haromaster87

So you said you did a rebuild of the engine in your car? How extensive was your rebuild? Did you do it yourself? Do you mind me asking the cost, roughly?

Pistons and liners were the most expensive part. I installed new valves, springs, '05' camshaft, followers, sprockets, chains, oil pump, guides, rails, turbo upgrade, injectors set to max spec, block bushings (hard to find) for the IP drive, pretty much everything that I could buy new OE I bought.

As I recall, the parts list was about $2,700....IIRC anyways.

I did all the machine work and labor myself.

funola · #7 09-29-2012, 05:34 PM

A few questions:

"6 months of running on 100% VVO"

What is VVO?

Somewhere I've read you run a 160F T-stat. What are the positives and negatives from running such a low temp stat? Have you measured you oil temperature in the sump?

Driving at 120 mph for hours on end, what was your engine oil consumption? Sounds like you have a well tuned machine to be able to go that fast for that long. Are there speed limits out there by you?

Secondaries · #8 09-29-2012, 06:46 PM

So... I get 21.5 plus or minus half an mpg running on B100, commuting 20 miles one way, mostly highway at 70-90 mph in my turbo wagon. Does that sound about right? Should i see more?

Doktor Bert · #9 09-29-2012, 11:12 PM

Quote:

Originally Posted by funola

A few questions:

"6 months of running on 100% VVO"

What is VVO?

Somewhere I've read you run a 160F T-stat. What are the positives and negatives from running such a low temp stat? Have you measured you oil temperature in the sump?

Driving at 120 mph for hours on end, what was your engine oil consumption? Sounds like you have a well tuned machine to be able to go that fast for that long. Are there speed limits out there by you?

VVO = Virgin Vegetable Oil

I burn about 1 pint every 5000 miles of use. Doesn't seem to matter how I drive the car, the oil consumption is predictable and consistent.

Yes, we have limits and I was definitely breaking the law, but I did get passed by a Mini Cooper at about 115mph....

Doktor Bert · #10 09-29-2012, 11:14 PM

Quote:

Originally Posted by funola

Somewhere I've read you run a 160F T-stat. What are the positives and negatives from running such a low temp stat? Have you measured you oil temperature in the sump?

Never bothered with oil temp readings. We ran my Dad's 617.951 over 400,000 with a 60°C thermostat and when we opened it up (because he was scared of it) everything looked like new and the ridge in the cylinder wasn't very pronounced.

I just keep doing what has worked in the past. No real science to it, just repeat results....FWIW

Doktor Bert · #11 09-29-2012, 11:15 PM

Quote:

Originally Posted by Secondaries

So... I get 21.5 plus or minus half an mpg running on B100, commuting 20 miles one way, mostly highway at 70-90 mph in my turbo wagon. Does that sound about right? Should i see more?

Sounds reasonable to me....

ROLLGUY · #12 09-29-2012, 11:35 PM

Quote:

Originally Posted by Doktor Bert

I frequently run between 100-115 mph, when my side of the freeway has minimal traffic.

I have to say I miss being able to wring 155 mph out of a car every now and then.

Don't you know that is illegal?

Doktor Bert · #13 09-29-2012, 11:39 PM

Quote:

Originally Posted by ROLLGUY

Don't you know that is illegal?

Yes. And it was also illegal to have my entire windshield in the 116 tinted today, but it looks cool....

My Mustang is so incredibly fast that it's almost impossible to physically.visually keep up with the car's velocity. It's like watching a movie while it is being fast-forwarded.

This was certainly illegal too. Filmed within 1/4 mile of a CHP staffed weigh station on Interstate 15....

http://www.youtube.com/watch?v=3HWkIOLexmw

treetrimmer · #14 09-30-2012, 12:13 PM

Quote:

Originally Posted by Doktor Bert

Never bothered with oil temp readings. We ran my Dad's 617.951 over 400,000 with a 60°C thermostat and when we opened it up (because he was scared of it) everything looked like new and the ridge in the cylinder wasn't very pronounced.

I just keep doing what has worked in the past. No real science to it, just repeat results....FWIW

Imagine how efficient it would be if you let it get up to proper operating temperature. Diesels are more efficient and run better hot, at least up until they are overheating. Why you would want a cold running diesel is beyond me.

funola · #15 09-30-2012, 12:18 PM

Quote:

Originally Posted by Doktor Bert

Never bothered with oil temp readings. We ran my Dad's 617.951 over 400,000 with a 60°C thermostat and when we opened it up (because he was scared of it) everything looked like new and the ridge in the cylinder wasn't very pronounced.

I just keep doing what has worked in the past. No real science to it, just repeat results....FWIW

Maybe if your dad ran the proper thermostat, the not very pronounced ridge in the cylinder would be no ridge instead?