Hey folks!

before I get into the heart of the matter, I just want to offer my thanks for all the support and help from this board and from the M/B community as a whole. I jumped into owning my '82 300SD last January and have had one hell of an education. She is a fantastic car, hands down.

I bought the car in Colorado for $1000, rust free, and drove back to Maine in 36 hours, straight. I've since done my best to bring her up to snuff; new glow plugs, relay, valves properly adjusted, timing chain, radiator, water pump and so on.

The reason behind the purchase is I'm a club DJ, and I tour up and down the East Coast to make my living. I wanted something comfortable, safe, reliable and bullet proof. So far, 9 months with 35,000 miles things have been great. The one thing I can't fathom is how wildly my mileage fluctuates.

My driving is 99.9% highway; I usually set an average cruising speed of 70 MPH. I run clean diesel, filters changed regularly, same with oil, and my MPG is all over the place. This summer, with the AC on, I would see 27.7 MPG, then drop to 23, then 21, randomly. More of the same recently - on one long road trip I averaged 27.6, only to drop to an abysmal 21.1 the week later when doing a 200 mile round trip to Boston and back. Tonight on the same run I averaged 22.1 when three weeks ago it as 26 and change.

At this point, I'm stumped. I'd love to get her to run at least above 25MPG - tires are properly inflated, I think I've done all the tricks. At this point I'm eyeballing the injectors and wonder if popping for five rebuilt units would be the next thing to do (Diesel Purge was done two months ago).

Total mileage on the odo right now is 326783. Burns no oil!

Many thanks again,

-James S.

The A/C compressor takes a really big toll on economy. It is used on most every climate control setting except economy and off.

Check all your fuel lines, tank cap and tank breather for signs of leaks.

I'm betting it is a fairly simple thing. A bubble or air space in the fuel tank. I always fill up at the same station, with a high volume truck pump, and my car sits at a slight angle on the concrete pad by the pumps with the left front down. After the pump kicks off, I can put in almost another gallon by "burping" the car, i.e. shaking it gently and letting the bubbles/foam in the fuel settle. (one has to have a lot of patience to do this, especially if people are around watching you shake your car!)

If I fill up at a regular "slow" pump, with my car on a level pad, (most gas stations) I probably wind up with about 2 less gallons in the tank, and can't get any more in no matter how much burping I try.

I figured out this was happening based on big variations in fuel mileage at different gas stations - I track every single tank. You are filling up at different stations all the time, from your description.

Anyway, that's my guess!

Rgds,
Chris W.
'95 E300D, 274K, with 90 liter tank

Its been cold lately, does the thermostat let the engine get all the way to operating temp? (just above 80C on the gauge) A cold engine will use more fuel.

Oh the other thing, to get your mpg do you fill up and then divide miles driven by gallons added? The ONLY way to get reliable numbers is to always fill up the same way (hold the handle until the pump stops). The way to get super reliable numbers is to always use the same pump...

Guessing in any way will produce wildly varying numbers...

Not saying thats what you're doing but that is surely how people on eBay get their mileage numbers.

__________________
Sadly Benz-less

Assuming you're measuring MPG's correctly I'd look for three possible causes...

1) Fuel leaks

2) Dragging brake caliper

3) Intermittent odometer failure

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I'd put money on the air bubble problem also. Fillups tank to tank with the small tanks can vary quite a bit. If you were measuring mileage with a 50 gallon tank then you might have some good data. Try averaging 4 fillups at a time and seeing if you get
variation.

You may find that you are getting around 25mpg average which isn't too bad. EPA estimate was 27 when new - and that was at 55 mph. I kind of doubt that you are actually getting better than that at 70 mph. There should be at least a 10% drop in efficiency going from 55mph to 70. Which means you should be getting around 24 mpg at that speed.

Remember, any resemblence between Ebay, Craigslist and "hypermiler" claims and reality are purely a coincidence.

BTW - I was at in a discussion regarding fleet vehicle fueling a month or two ago and one member was discussing a study he did on actual fuel and mileage records versus what the drivers were claiming. He summed it up with these words: "I realized that people lie a lot."