Good afternoon everyone! My name is Will, first post here. I've already learned quite a bit reading around old threads here, but still looking for some advice. If this is in the wrong forum, I apologize in advance and hope someone will move it for me.

Skip down to the bottom for the TL;DR.

Before I start, just some quick info about myself. I've noticed there are lots of international people around here, so just to clarify, I'm in the 'States. North Carolina to be specific. Young guy, mechanical engineer, and plenty able to work on things myself. I've built the motor, transmission, and rear end in my supercharged Mustang. Also have rebuilt the engine in my daily driver, an '01 Honda Civic. The point of all this, is that I'm quite capable of working on something. That said, I don't like doing it all the time, and hence why I'm here.

I'm looking to replace my current daily driver, a manual transmission 2001 Civic. I've had it for many years now, but with almost 350,000 miles on the clock, it's getting to the point where it seems like I'm working on it every few weeks. Combine that with the fact that it is so unbelievably boring to drive, and that I'm no longer a broke college student, and I'm just ready to move on.

Some more info about me: I drive around 30,000 miles a year to and from work. Literally 95% of the drive is interstate, where I ride at 70 mph with the cruise control on. To keep my yearly fuel costs down, highway fuel economy is very important to me; my goal so far when looking at a new ride has been at least 30 mpg on the highway. I have been impressed with my Honda concerning fuel mileage and overall cost to operate, and after looking at lots of different cars, I decided on getting a 2006-2007 Honda Accord, 4 door, V6, with 6-speed manual. It hits the 30 mpg highway check box, pretty roomy inside, has a nice 240 horsepower, and a nice transmission. Also, at roughly a $7000 price tag, the depreciation won't kill me on it either.

Still, it's a pretty boring car, without any real 'soul', and $7000 is on the upper limit of what I'm willing to spend for a car being driven 30k-40k miles a year. Regardless, this is the baseline I'm comparing everything to.

Enter Mercedes. I hadn't considered one during my search for a couple of reasons. 1, I'm not a huge fan of German long-term quality (or at least my perception of it). And 2, (kinda related to #1), they aren't available in a manual, or at least are very rare. I plan on driving a DD until it has at least 300,000 miles, and I tend to believe that autos, on a percentage basis, don't hold up for that long nearly as well as a manual does.

BUT, after some first hand accounts and good ole internet research, I've come to decide that a W124 Mercedes may offer what I want in terms of reliability, and whatever it sacrifices in fuel mileage, it should more than make up for in terms of a sweet looking ride with a lot of soul, as well as quite a discounted entry price well below the $7000 tag of the Accord. That being said, I still want to make an educated decision.

Assuming gas averages $2.50 a gallon over the next 3-4 years (it's currently $1.50 here, but I'm assuming it'll go up a good bit), the Accord would cost $2500 a year to drive to and from work. If I got 25 mpg from an old gas-burner W124, that yearly cost would be $3000 a year. Assuming I got the Merc for a good bit less than $7000 (which seems very reasonable), that'd be a breakeven point of several years, which I'm perfectly OK with. I'd prefer to go diesel, but it is roughly 25% more expensive here, so I'd need to get roughly 32 mpg from a diesel to equal the driving cost of a gas version (assuming it got 25 on the highway).



So, the TL;DR. What is the best gas model W124 for fuel mileage? Best diesel model for fuel mileage? Are my proposed numbers above possible (25 mpg for gas, 32 for diesel)? What are reasonable numbers I can expect on the highway at 70 mph? Best for reliability (I hear they're all roughly the same, just little quirks here and there)? I'm not particularly keen on the post-facelift models, so I want to keep it prior to 1993 or whenever they changed over. While more power is virtually always better, I'm ok sacrificing some in exchange for fuel economy.

From my reading, it looks like my best gas bet is a 260E or 300E 2.6, and my best bet with a diesel is the 90-93 300D with the turbo 2.5. Opinions?

Is $3000 going to get a decent gas model? $4000 for a decent diesel? Knowing that I plan to keep this and put at least a couple hundred thousand miles on over the coming years, I don't really want anything over 150k miles. Around 100k would be preferable, but I know those are getting rare and I'd have to pay for it.

Also, is it an option / worthwhile to swap a taller geared rear diff from some other model? I'd assume that the V8 models might have taller gears, and swapping those into a I6 or diesel model would potentially help highway fuel economy out quite a bit.

Thanks in advance for the help!