i'm heading to out of town for about 30 days.
The 240d will not be driven during that time.

Is there anything I should do to her while she waits?
Doesn't seem like enough time to warrant disconnecting the battery or adding anything to the fuel, but I'd rather be thorough and find out.

And in the interest of posterity (future search strings), is there a safe upper limit on how long these diesels can be parked without being driven?

For 30 days you need do nothing. In any case, with a full fuel tank, a 240D would probably idle for 30 days and be ready to rock on your return.

I'd disconnect the battery for the heck of it. And chock the wheels rather than engage the park brake.

I would think it'll lie dormant indefinitely. It's more a matter of what you do to put it back in service depending on how long it's lain dormant.

Sixto
83 300SD
98 E320 wagon

30 days is nothing. Just park it and start it up after you're back. Betsie is parked and dormant for about 7 months each year (can't drive her in winter). When I park her I top off fuel, throw some anti gel in and take out the battery. Pump up tires to 55 psi to prevent flat spots and stuff those metal scrubber sponges down the intake and exhaust to prevent critters crawling up there. Come spring I reverse all that, turn key and go. Well, I do zip tie the stoplever and turn the engine over with the starter until I get some oil pressure, but after that it's starting and going. You'll be fine.

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)

Great advice, thank you all. I read somewhere about wheel bearings getting pitted if the car sits too long? There's a chance in a few months I'll have to garage my car for about a year. Controlled environment, shouldn't be too harsh on her. Wondering if I should put it on blocks rather than over inflate the tires.

Shern, the blocks vs. tires storage controversy comes up occasionally. My opinion is that a car's natural position is with it's weight on the wheels and suspension. It spends it's whole life in that position. To suspend it on blocks for a long period may be marginally better for the tires but it will stress the suspension and steering components.

I just woke mine up from "winter" storage yesterday. All I did when I put it away was fill up the tank and set the tires to 35 PSI. Started right up and drove yesterday with no issues. I figured it was safe to get it ready for spring a bit early since we haven't had much winter so far.

Maybe if it sits for decades? My SDL sat in a field for 10 years untouched and the wheel bearings are fine. Silent and smooth. Center bearing on the driveshaft is another story (soon to be resolved).

If your tires cost any more than $35 when new, they should be able to sit for a year or two and be fine with no ill effects. You may have a bit of a thump or wobble for the first few miles you drive it, but any decent tire will smooth right out as soon as you get some heat in it. My SL has the same tires it came home with in 1998 and despite it sitting for 6-8 months at a time (sat 4 years once), it still rides nice and smooth.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Get a set of junk wheels to sit on while stored on the chance you'll store it long enough to develop flat spots but not long enough to develop dry rot :/ Or set jack stands under the outboard ends of the control arms.

Sixto
83 300SD
98 E320 wagon

This has my vote. Very easy to do, and the suspension and springs will not know any difference for the month/s it is sitting dormant. I would also cover it if it is outside......Rich

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All Diesel Fleet
1985 R107 300SLD TURBODIESEL
2005 E320 CDI (daily)

LOTS of parts for sale!


EGR block kit
http://www.peachparts.com/shopforum/diesel-discussion/355250-sale-egr-delete-block-off-plate-kit.html

1985 CA emissions 617 owners- You Need This!
Sanden style A/C Compressor Mounting Kit for your 616/ 617 For Sale + Install Inst.

Sanden Instalation Guide (post 11):
http://www.peachparts.com/shopforum/diesel-discussion/367883-sanden-retrofit-installation-guide.html

Yeah, taking the weight off the tires for long term storage seems like a good precaution.....OTOH if the tires are damaged by the sitting they are probably in need of replacment anyhow.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Much appreciated gang!

Mothballs in the trunk & cabin to keep critters out. They repel mice/rats/bugs too

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment