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Old 06-20-2010, 07:36 PM   #1 (permalink)
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Help! Need specifics on MPG 300d and sd

Hello, I'm considering purchasing a 1981-1985 300d or sd but I'm not getting any solid gas mileage figures.

My commute is about to be 80 miles a day and I thought an old reliable Mercedes diesel would be the perfect vehicle for my mostly highway commute. The problem is looking through this forum I'm getting all kinds of figures. 18-35 MPG.

Any advice would be much appreciated!

Thanks.
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Old 06-20-2010, 08:06 PM   #2 (permalink)
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The weight and aerodynamics (or lack thereof) of either chassis can have a negative impact on fuel mileage. Mileage also suffers at highway speeds due to final drive ratios resulting in high engine RPM. Engine condition also contributes to mileage and can explain the wide range in figures.

123 and 126 diesels made excellent long-distance commuters due to their reliability, ease of maintenance, and comfort.

I made a 60 mile per day commute in a 300 D for years; the chassis failed before the drivetrain, which was perfect at over 410,000 miles.
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Old 06-20-2010, 08:40 PM   #3 (permalink)
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Have driven 2 300 SD's for over 300,000 miles. Still own one, an 84. With a fresh tuneup I routinely averaged 29-31 MPG on the freeway at between 55-70 MPH. This routinely gave me 600 miles with reserve on a tank of diesel, not gas. One the station slipped me $10.00 in Premium and the engine was toasted by the time I realized that something was the matter except for unusually high fuel useage. The station responsible replaced the engine with a junker engine that used excessive oil and fuel and blew in 4,000 miles. Still have car but it was replaced with an 84. Again with a new cam chain, replace timing chain every 200,000 miles and tune up every 25,000, and of course change all 8 liters of oil with a good oil, Not Chevron or Valvoline or Castrol. Keep the injector timing at 17.5-18.5 degrees after top dead center. and you will keep optimal performance for open road mileage.
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Old 06-20-2010, 09:15 PM   #4 (permalink)
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Before I retired I used to drive 140 mile round trip for work, 90% freeway. When I drive at 70+/- or with the flow of traffic, I got a pretty consistent 25 MPH. For the last year and a half before that because diesel went over $5 a gallon, I drove a consistent 55 MPH, always using Cruise Control. I averaged 30+ MPG. It can be a bit scary to drive like this. Since I no longer do that commute, it has dropped significantly. You can see it in the graph below. If you click on the graph you can read any comment, about the driving conditions, I may have made about that particular tank of fuel.

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Old 06-21-2010, 04:33 AM   #5 (permalink)
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Thanks guys, all of this is great news.

What about simple after market mods - like a K&N air filter?

This is interesting since not a single responder has mentioned sub-25 mpg.

Last edited by mrbondmi6; 06-22-2010 at 06:18 AM. Reason: typo
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Old 06-21-2010, 11:39 AM   #6 (permalink)
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how is that possible??

even at 7,500 lbs this guy gets 25 mpg.
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Old 06-21-2010, 11:43 AM   #7 (permalink)
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a realistic figure would be more in the low/mid 20 range unless you have the deathwish of driving 55mph
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Old 06-21-2010, 04:08 PM   #8 (permalink)
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Quote:
Originally Posted by mrbondmi6 View Post
Thanks guys, all of this is great news.

What about simple after market mobs - like a K&N air filter?

This is interesting since not a single responder has mentioned sub-25 mpg.
Here's your first sub-25 mpg response. I average about 22mpg combined driving in the 1982 300D Turbodiesel.

Also, K&N will not help you. Unlike other makes, your stock filtration system and stock filter is more than sufficient for your engine.
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Old 06-21-2010, 05:32 PM   #9 (permalink)
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I average around 23-24mpg combined. Fuel consumption increases when I use AC, more so when I hit 80mph on a regular basis. If I drive 60-65mph, I can get it up to 26mpg without AC. With AC, that drops to around 24.

If you want to see better MPG, check eBay
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Old 06-21-2010, 06:38 PM   #10 (permalink)
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Quote:
Originally Posted by mrbondmi6 View Post
Thanks guys, all of this is great news.

What about simple after market mobs - like a K&N air filter?

This is interesting since not a single responder has mentioned sub-25 mpg.
People say they notice a significant difference with the K&N setup yet they fail to provide real numbers before and after the changeover.

The stock air filtration setup provides more than enough air for the engine to breath so leave it as is.
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