Pulled the glow plugs on my 4sp 240d a few weeks ago and found healthy plugs but fairly coked holes. Reamed them by hand using a variety of drill bits, reinstalled and voila.
25/26 mpg has become 30mpg (after 3 tanks).

I'm inclined to believe it's a fluke but I've controlled for driving style, distances travelled, fuel type, etc. This seems to be the only variable.

Has anyone experienced similar results?
And if so, can you explain the mechanics behind the effect?

If you get winter diesel in the winter, I saw the switch a couple tanks ago. I went from 25-26 mpg to about 28 in my 300TD 4spd. Otherwise, that could be the case too. 30+/- is normal for a 240D

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My fuel economy went up the last 3 tanks as well on my diesels. It's the change of season, the fuel blend is no longer winter fuel. Reaming the glow plugs will barely impact economy, maybe 0.5mpg if anything.

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Glow plug holes? Do you mean prechamber holes?

In the pic there is a red rectangle. Glow Plug reamers ream out the Carbon between the heating element of the Glow Plug and the hole through the prechamber and mostly the cylinder head.

When carbon builds up there part of the heat gets transferred into the cylinder head and not the Air in the prechamber.

Attached Thumbnails

 

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Shern - FE is a VERY tricky thing to measure repeatably. EPA does all their FE measurements on the dyno so that variables like ambient temps, humidity, driving cycle, etc. can be mitigated. On the road you're not in charge of those variables and they all have their effects on the FE numbers.

I actually ran the EPA FE tests on a test track at TRC in Ohio with calibrated instrumentation. We ran using a highly accurate fuel meter and a 5th. wheel for speed (these were the Olden Days) hooked up to a strip chart recorder that gave the driver the same exact driving cycle as used on the dyno. We didn't run in the rain and only ran if the ambient temp was between 68-86*F (30-40*C), the lab standard. All the fuel used was lab-standard individually analyzed fuel blends as used at the Lab (Indolene HO for the gas-fueled cars). With all these requirements and more we got about the same mean FE values as the same cars got on the dyno. However, the scatter (standard deviation) was much greater.

My point in all of this is that people think FE is a simple measurement and it isn't so you can't place too much importance in these on-road values. And as the guys have pointed out, a single change such as the fuel blend throws all your carefully-gathered data out the window.

I admire your scientific curiosity and I think you gathered your data as carefully as a person can in a non-professional situation but FE is, at best, tricky. Surprisingly, the on-board fuel economy measurement systems in many modern cars are probably about as good as you can do for on-road FE data.

Dan

Thanks Dan -my methodology was incomplete to be sure =)
Figured anecdotal evidence was as good as it'd get.

Regarding the winter fuel/summer fuel transition, is this something that also occurs in warmer places of the country? I live in Los Angeles where we don't experience seasons so much as nuances.

There are just two many variables. Cleaning out the carbon is not going to be a bad thing though.


All 240ds do not seem to produce the same fuel milage. There is about a five miles per gallon varience. Many over the years have reported about 25 miles per gallon. While others reported in the 30 miles per gallon range. Just too many reports and I have never found a reason. The majority of these reports where posted by people with longer term ownerships.


Mercedes did some experimentation with the hole sizes in the pre chambers I understand. I do not know what reached production. A check of different part numbers for the pre chambers for different years may reveal something. If you can reach about thirty miles per gallon on the highway consider yourself fortunate. Many 240Ds cannot it seems. While many can.


It has bothered me for a long time as the five cylinder engines do not seem to have this issue. The non turbo charged five cylinder delivers less fuel milage than the turbo charged versions. Yet those that have added a turbo to their four cylinder 616s have not reported a milage gain. Yet on longer trips turbo or no turbo the cruise speed was probably similar. There is just something in this area with the four cylinder 616 I probably will never find if it exists.

That's really interesting. They sure are quirky machines... I've performed the most minor maintenance and everything seems to change. Maybe I'm changing

Don't overlook the temperature you're driving in either. Warmer weather will net you increased fuel economy due to less air density (richer mixture) and increased tire pressures resulting in reduced rolling resistance. In a 74hp car, that matters. Add in a better fuel blend and you're talking 3-4mpg easily.

The turbo cars are largely immune to the effects of air density since the charge pressure is regulated by the wastegate, not by atmospheric pressure.

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Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

617 na vs turbo US spec vehicles with the auto trans get lower economy due to the short diff, and the slipping torque converter.
It isn't really the turbo that gains economy in the aspirated vehicles... it's the diff change.

Put the 3.07 or 2.88 diff behind the na motor, and economy would go up... of course, it would take a month to reach 60mph... the trans gearing and shift points in the na vehicle also hinder economy in favor of spirited city driving...

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My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Graminal95 reported big mpg gains when they turboed the 616. They also put in a an intercooler and used a 5 spd too, I think. It might have just been the 5 spd. the owner of the 616 I bought said they were up around 40 mpg with the 5sp.

Blast from the past>>http://www.peachparts.com/shopforum/diesel-performance-tuning/250021-intercooler.html

I had forgotten about all the salt spilled in those days:


MTUpower MTUpower is offline
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So you agree that you were incorrect in your absolute "zero" statement? A simple yes or no will suffice.
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#24 Report Post
Old 04-25-2009, 10:19 PM
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I never made an absolute statement, you continue to make assumptions despite the simplified decription I provided for you in the post above.
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#25 Report Post
Old 04-25-2009, 10:21 PM
MTUpower MTUpower is offline
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Quote:
Originally Posted by ForcedInduction View Post
"zero power and economy difference with and without my intercooler."

Here to refresh your memory.
Brian said marginal, you said zero.

http://www.peachparts.com/shopforum/diesel-discussion/235835-5-speed-my-240dt.html

http://www.peachparts.com/shopforum/search.php?searchid=7742113





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__________________
CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?