87 300TD: 6K mls of less than 27 MPG & 1 fix got me 30.1 MPG - Here's how.
 

I replaced a bunch of cracked vacuum tube connectors. That's it! The wagon was shifting hard so I went through and checked all the vacuum connections for leaks. Some connectors broke apart in my fingers. Not only did the shifting go smoother, the mileage took a nice bump! :)

Sweet :)

I will need to do this, right now mine doesn't shut off without popping the hood open. I know it's likely bad lines causing leaks. I guess I just need a big bag full of new rubber unions.

I can help you with this.

Wow, I have never gotten more than 28 from my wagon in any driving circumstances. I average 25-26 (and that is without AC). This has been the case for 40-50k. Vacuum lines have been gone through and are intact as far as I know.

How long has it been this level? I would like to know how long it stays how many tanks you make it over. 30.1 MPG is near impossible that heavy wagon for any sustained time.

I get 25 mpg in mostly city driving and 34 mpg in mostly highway driving in an 1987 300TD. These are real, verifiable numbers over several tanks. I describe a couple of these tankfulls here in post 87:
http://www.peachparts.com/shopforum/diesel-discussion/279144-realistic-mpg-300ds-300sds-190-ds-6.html

Next, I plan to switch to synthetic oil to see if I can squeek out another mpg to get 35 mpg highway.

My last two tank fulls were 29.1 and 29.7, respectively. :-)

odo?
 

How confident are you in your odo?

The speedometer is spot on. Next long trip I'll validate the odometer, but for now I've no reason to question it.

I should also mention that I'm running 195/65-15 Michelin XVS+ with less that 2,000 miles on them, and they are properly inflated. I do not have the roof rack cross bars installed. The air conditioning is NOT charged, so there is no drag from the A/C compressor, but that means the windows and sunroof are generally open.

Finally, I replaced the leaking transmission vacuum control module just before the last two tank fills, plugging what I believe was the last vacuum leak.

Tank fills, are the only way to determine what your car's mpg is IMO.

My '06 E320 CDI's on-board computer registered; "40.1 mpg" on it's maiden voyage from San Antonio to Dallas, Texas. That's the good news. The bad news is that an RT (round trip) to the taco stand .75 miles each way from my home, yields 18 mpg in the car. The city driving is yielding 24 mpg. The moral of the mpg story is that any isolated mpg reading is just that - isolated. Real world, out-of-pocket costs to replenish your fuel tank(s), unfortunately, are not based on your best mpg reading(s). When some joker claims his '99 E300D yields; "43 mpg" here on-forum, I just laugh at it. My same car has never yielded over 32 mpg under any circumstances per tank fill-up. The car is not capable of; "43 mpg." End of story.

Likely climate control vacuum pods also.

My engine bay is running out of vacuum hoses. I only ones I have left is the engine shut off, brake booster and climate control hose.