What MPG's should I expect from this swap? - PeachParts Mercedes-Benz Forum

smallwwb · #1 03-12-2012, 10:33 PM

Posting a question to the ether:
What kind of fuel mileage should I expect from a 240d 4spd with a OM617.95x swapped in? I could also swap the rear axle from a 1985 300d.
My current car is said 1985 300d with 192k, vacuum leaks have been fixed, new injectors a year ago, not yet done valve adjust. Everything else stock.
My car has body damage and a salvage title, plus bad HVAC system.
I have a line on a mint 240d in perfect condition but for a bad top end on the engine. I can get the car for cheap, and figured I could sell off the parts I didn't need after the swap to recoup my investment.
I get 25mpg pretty reliably right now, so for it to be worth the time and effort, I'd want to get 35+ after the swap, keeping the a/c system.
I've read lots of posts about swaps, but no mpg numbers for this specific setup.
Thoughts?
Thanks!

ROLLGUY · #2 03-13-2012, 12:42 AM

I think if the only thing changed is the engine (keeping the 4 spd behind the 617), your MPG would not be what it was with the 4 cyl. I am not familiar with the OM617 numbers, but if it is a turbo, you would need to change the rear end ratio (higher=lower numerically) to get anything close to 30 MPG. (EDIT: just re-read that the donor is an '85, so it is turbo)
If you are close to CA, I could use a 240 bottom end!

ROLLGUY · #3 03-13-2012, 12:51 AM

If your donor engine has CA emissions (trap ox etc), I suggest you get a set of manifolds from a '78 or '79 300SD (no EGR). You can also simplify the vacuum system and only have vacuum to the trans, door locks, CC, and shutoff.

Skippy · #4 03-13-2012, 06:12 AM

With the '85 rear end you should be able to break 30 mpg, depending on how you drive.

t walgamuth · #5 03-13-2012, 06:35 AM

I agree. You should, if the engine is sound, be able to get 30 to 32 highway running 70mph on a trip on the interstate in a 123 body with the 288 diff and a turbo motor.

smallwwb · #6 03-13-2012, 11:59 AM

I drive like an old lady, never floor it, 55-60 on the highway, etc.
I have already simplified vacuum lines and blocked egr, pipe is straight from turbo-back to stock muffler. (No smog stuff)
So if I'm only going to get 32, it's probably not worth the effort, since I get 50% of my fuel for free...WVO
I thought if I used some hypermiling techniques, plus my trans is a bit tired I'm sure... The 240's are a bit lighter...
Anyone out there have this setup that can post real numbers?

JB3 · #7 03-13-2012, 12:07 PM

the 4-speed has the same final ratio as the automatic- 1-1, so that won't really get you big numbers, but having the manual will make you able to increase your hyper-miling driving techniques, which could make a pretty big difference.

I tried shifting earlier and keeping rpms low in my VW, and increased my mpg by 3-4 mpg! you could pick up some at least. The swap I think it worth it anyway for the added fun.

If you keep the 240 rear end though in the body donor and move the engine, you will probably get worse mileage.

charmalu · #8 03-13-2012, 03:21 PM

The 240D has a 3:69 Diff, the 85 300D uses a 2:88 Diff;
82 - 84 300D use the 3:07 Diff.

I have a 240D 4 spd in our 85 300D with 2:88 Diff. on the Highway we see up to 31 mpg. that swap gave us an additional 3mpg increase.

Use narrow tires aired to the Max side wall recommendations, drive slower, and the numbers might go up a bit. Don`t expect 35mpg constantly. only on E-Bay do they do better.

Our 80 240D 4-spd with the 3:58 Diff will get us 31 pluss mpg.

Dropping the 617.952 engine into a 240D will give you a simpler car overall. manual climate control. manual window winders (except for 82 & 83 have electric windows) and in some cases a manual sunroof.

I don`t know is the 240 is lighter, it is still a W123 body, but the differences in engines and transmissions have an effect. when I pulled out the auto and installed the manual, the front end came up a bit. then added 240D springs to drop it back down.

Charlie

t walgamuth · #9 06-21-2012, 05:43 AM

Quote:

Originally Posted by smallwwb

I drive like an old lady, never floor it, 55-60 on the highway, etc.
I have already simplified vacuum lines and blocked egr, pipe is straight from turbo-back to stock muffler. (No smog stuff)
So if I'm only going to get 32, it's probably not worth the effort, since I get 50% of my fuel for free...WVO
I thought if I used some hypermiling techniques, plus my trans is a bit tired I'm sure... The 240's are a bit lighter...
Anyone out there have this setup that can post real numbers?

Driving like that you may reach 35. It'll be close.

I would not worry about the extra weight. It will only matter around town and that will be so small it will be tough to measure, IMHO.

charmalu · #10 06-21-2012, 10:57 AM

A couple fat chicks in the back seat will weigh more than the difference between the two cars.

Charlie

smallwwb · #11 06-21-2012, 10:58 AM

Charlie did you pull the trans out and bolt them together then put them in as a unit? I'm still going back and forth about which body to use...

Renntag · #12 03-14-2012, 07:01 PM

Quote:

Originally Posted by smallwwb

Posting a question to the ether:

No idea who that is, but I'll give this a shot.

Quote:

Originally Posted by smallwwb

What kind of fuel mileage should I expect from a 240d 4spd with a OM617.95x swapped in?

Well there are too many unknowns here. If we make assumptions across the board and say your donor 617 is in a good state of tune and it making more power, mileage may be the same. The car will be more powerful and thus keep up with modern cars more easily.
Note that to a certain point, having more power requires a lower percentage of output to do the same work. At a point mileage will be better.

Quote:

Originally Posted by smallwwb

I could also swap the rear axle from a 1985 300d.

knowing the ratio of each is of more benefit. As mentioned above, a lower ratio will allow the car cover more distance for each revelution of the drivetrain. Thus better mileage.

Quote:

Originally Posted by smallwwb

My current car is said 1985 300d with 192k, vacuum leaks have been fixed, new injectors a year ago, not yet done valve adjust. Everything else stock.

Looking for mpg, consider EGR elimination, and adding water injection. Reducing intake temps will improve efficiency and help steam clean the intake tract.

Quote:

Originally Posted by smallwwb

My car has body damage and a salvage title, plus bad HVAC system.

Time to take it out to pasture. One bullet to the head.

Quote:

Originally Posted by smallwwb

I have a line on a mint 240d in perfect condition

If the body is good, you could swap interior pieces to eliminate the sun damaged stuff.

Quote:

Originally Posted by smallwwb

but for a bad top end on the engine.

I know what you are trying to say....but jeez.

(LOL: Is there a top end NOT on the engine?)

Quote:

Originally Posted by smallwwb

I can get the car for cheap, and figured I could sell off the parts I didn't need after the swap to recoup my investment.

Smart.

Quote:

Originally Posted by smallwwb

I get 25mpg pretty reliably right now, so for it to be worth the time and effort, I'd want to get 35+ after the swap,

I believe that is beyond what a 300D can achieve. Expecting 25-30 might be reasonable. Beyond 30mpg you will have to address greater system efficiency.
Forced inducted systems see high intake temps. Reducing these temps will increase efficiency. Inject water you can get for free and see improvement in performance and efficiency.

Quote:

Originally Posted by smallwwb

keeping the a/c system.

As you should.

Quote:

Originally Posted by smallwwb

I've read lots of posts about swaps, but no mpg numbers for this specific setup.

It is quite subjective. Typically you can expect 24-30mpg from this vintage when driven economically.

Quote:

Originally Posted by smallwwb

Thoughts?

Cant really think of anything.....

If you really want greater efficiency consider an OM603 or 606 swap. The newer more efficient motors will better reach your 35mpg+ goal. Possibly even 40mpg with a 606 in a W123.

Quote:

Originally Posted by smallwwb

So I took a look at the "mint" 240d today, and it's totally sun-rotted inside, with terrible paint, stained carpet, etc. Not mint at all.

Have pictures to share? Curious what it looks like.

Quote:

Originally Posted by smallwwb

I'm thinking it might be a better idea to find a 5spd from something else.

That might prove difficult.

aaa · #13 03-14-2012, 08:00 PM

The trans'll work, will the shifter stuff work?

Generally you don't count on finding w123 5 speeds, they're too rare.

ROLLGUY · #14 03-14-2012, 10:51 PM

Quote:

Originally Posted by aaa

The trans'll work, will the shifter stuff work?

Generally you don't count on finding w123 5 speeds, they're too rare.

Yes, you may be able to find a 5 speed, but it may cost more than the car is worth!

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