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Old 10-21-2003, 06:17 PM
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Join Date: Dec 2002
Posts: 75
Diesel Economics - Should I really trade in my gasser for a Diesel

For the last month or so I have been seriously considering trading in my 84 380SE (98,000 miles) for a Diesel.

Primary reason for thinking of trading in (I can keep only 1 car)was the fuel economy. So I did some back of the envelope calculations based on 20,000 miles per year. Here are the numbers:

For 380SE (at 19 mpg)...1053 gal/yr......$ 1,590.03 per yr ($ 1.51 per gal in FL)
For 300SDL( at 26mpg)...769 gal/yr.......$ 1,161.54 per yr ($ 1.51 per gal for Diesel too)

Savings per yr...$ 428.49 or a mere $ 35.71 per month.

Plus, with a Diesel, I would need to do synthetic oil changes (@ $ 4.00 per quart) and add additives (lube moly purge, water sequesterer etc) more frequently than what I do in the gas engine. This further brings down the savings.

The 380SE would last me till 250,000 miles too. The diesel perhaps a little more.

Looking solely from the savings viewpoint, there does not seem much of a point in trading in. Am I missing something ?



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Old 10-21-2003, 06:35 PM
Senior Member
Join Date: Feb 2001
Location: Canton,Texas
Posts: 987
How often do you plan on oil changes? On the Diesel with synthetic you should be good at 7,500-10,000 mile changes. I think you're right though... if you have a good running car that will last why trade it for something else.
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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Old 10-21-2003, 07:44 PM
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Join Date: Jan 2003
Location: USA
Posts: 699
I'm a fan of synthetic oils, but I believe that using synthetic oils for extended periods in diesel engines is not good, because the compression ignition process produces too much soot, sludge and particulates (e.g. carbon) etc. that mix with the oil. Also, diesel (especially in the US) tends to relatively high amounts of sulfur, which will be oxidized and mixed with residual water (if you don't drive long enough to completely heat up the oil and vaporise the water) to produce sulfuric acid (H2SO4), an extremely corrosive chemical for your engine. Therefore, for diesel engines, frequent oil changes are necessary to remove soot/sludge/particulates and sulfuric acid.

I think the only 3 MAJOR reasons to consider using synthetic oils in diesel are:

1) Easier starting in very cold weather.
2) You want to treat your diesel car like a baby.
3) You have plenty of dough to spend.

However, please do not try to use synthetic oil in diesel engines for extended period of time (I think 5000-7500 Miles should be max for synthetic oils). Extended periods (with synthetic oil and 10-15 Kmiles) for gasoline cars where combustion process does not produce much dirty stuff are OK. Modern gasoline engines burn very cleanly.

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Old 10-21-2003, 07:44 PM
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Join Date: Nov 2000
Location: Vernon, CT
Posts: 1,848
For one, the additives that you add regularly would be something like Power Service. A whole bottle cost $3.47 at Walmart and is good for 100 gallons. Basicly the additives cost next to nothing, per gallon. Lubro Moly Diesel Purge should be done twice a year, costing a total of $20. Diesels have no sparkplugs, distributor caps, or rotors that require regular replacement. Using synthetic oil and the miles you drive, you would only do 2-3 oil changes a year, vs. 6. Just for basic math, look at the oil changes. A filter will cost $8 and 8 qts of oil, $32. So that is $40 per change and you do 2 changes a year, $80. Doing regular oil changes with dino oil, every 3K works out to $20 per change, times 7 works out to $140. So right there there is a savings. Actually that would apply to any Benz using synthetic.
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
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Old 10-21-2003, 07:54 PM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,552
Basically, your analysis is correct. Given current energy prices in the U.S., trading in on a diesel does not make economic sense. The fuel cost is such a small part of the overall ownership cost of an automobile that the opportunity for savings just isn't that great. It would take forever just to recover the sales tax you'd pay when registering the new diesel.

The big problem is that you'd be trading a (presumably) clean, low mile, well sorted 126 sedan for an unknown quanitity. If you budget what the 380SE will sell for, you'l be able to purchase a diesel sedan of about the same age with around twice as many miles.

Now, when looking for a new car I do somewhat prefer diesel. There are a couple of general reasons why. I find that MB diesel owners tend to take better care of their cars than gasser owners, in general. So it's easier to find a really clean old diesel than a really clean old gas car. I like all the low end torque a turbo-diesel supplies. I like the range - you can go for weeks without stopping to fillup. The savings in fuel costs is in there too, but it's pretty much bottom of the list.

Bottom line: keep your 380SE. Unless it doesn't meet your transportation needs or needs work that you are unwilling to invest in, I don't see it making sense to trade.

My $.02

- JimY
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Old 10-21-2003, 08:12 PM
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Join Date: May 2001
Location: Michigan
Posts: 1,373
I wouldn't trade even though I'm completely diesel. However, if you do decide to:

1. Search high and low for fuel savings. We have one station around here which is notoriously low. The last 2.5 months they were stuck on 1.309 compared to an average of 1.609 for gas. During that time, most of the diesel sold at other stations was 1.599. So, we're talking significant savings each tank.

2. I think diesel can be maintained cheaper. I buy the synthetic rotella at walmart for 12.88 per gallon when it goes on sale. Then, I only use it during the blizzard months. I buy oil filters by the dozen from performance products when they have their 15% off deal. $6 per filter.

However, I'd have to agree with the sales tax point made earlier. Why switch if you like your current setup. I would only consider if you were having problems with it.

'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

'82 240D 229k (Matt's - Converted-300DT w/ 4 speed
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Old 10-21-2003, 08:47 PM
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Join Date: Sep 1999
Location: SW Colorado USA
Posts: 296
I have a beef with the notion Eric extended on drain intervals for synthetics in diesels. There are a lot of trucking companies out there running 40-50 thousand miles between oil changes on heavy trucks with synthetics. Chevrolet sets the drain interval on my diesel pick-up at 10k miles, I have two Dodge diesels that reccomend 7500mile intervals. The last two use dino oil. I have done oil sampling on these trucks and the oil is still servicable at 10k miles, that includes soot and corrosives content. The bottom line, without trying to start another endless oil discussion, is that oil lasts a LOT longer than most people think, certainly longer than Jiffy Lube wants you to believe.

Back on the topic, unless you were driving a bunch more miles per year, stay with your"known quantity" 380SE. I find it doesn't really pay until you start racking up 50,000+ miles per year. I have also found that while a diesel may seem to require more attention, they really don't, it is just a different set of needs. Overall costs are very similar, fuel consumption is the major factor, and with domestic diesel trucks engine longevity is MUCH better on most diesels. As you already know,an MB gasser lasts an awefully long time
1995 G320
1984 280GE
1971 Unimog 416
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Old 10-21-2003, 09:27 PM
Registered Diesel Burner
Join Date: Aug 2001
Location: Northern Virginia
Posts: 2,911
I think you should keep your current car but budget right now for a timing chain replacement. RIGHT now.

1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles
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Old 10-21-2003, 09:36 PM
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Join Date: Sep 2003
Location: San Francisco Area
Posts: 124
A further narative with question instead of a real response to the original post. I have never had a Mercedes gasser, so I can't speak to its costs to be sure the comparison is valid,

But I've owned for years a large Audi, so maybe it approximates something of a mercedes gasser. On long distance I-80 type travelling The Audi is a pleasure to drive and gets great gas milage of 28 mpg when its running right. On the other hand, for around town driving of buying groceries, going to the bank, the kids school etc. it gets lousy gas milage and just feels too big.

Even though I've had the diesel only a couple weeks, the fuel costs are a lot less than the audi's for real city driving.

So in a sense I'm asking for confirmation heavy car for heavy car if a diesel's in city gas milage costs is much less than a gassers?
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Old 10-22-2003, 03:03 AM
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Join Date: Jan 2001
Location: oregon
Posts: 2,013
I have both a gas and diesel 126 and like them both ,but think I would keep the 380 as it has low miles and fuel is not the real cost of maintaining a car compared to insurance and general upkeep.............
William Rogers........
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Old 10-22-2003, 04:54 PM
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Join Date: Jun 2001
Location: CA
Posts: 531
That 380 is a fine engine - lazy, unstressed and long lived.

Change the rails, replace the chain and tensioner and fix any intake manifold leaks and you are set for another 100k miles @19mpg - the same mileage my wife's 1981 380SLC gets.

No speed demon, but quiet and long lived, and certainly more economical than the 560.

Others have said it well - the economic advantages are minimal. The lack of noise and smell in the gasoline version bears pointing out. I love my 300SD, but the 560SEL is a haven of peace and quiet by comparison.

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