Been there done that about 15 years ago. I had sooo much to learn, or rather "un-learn" from my days working American cars from the 70's and air cooled VWs.

Many many things are different, you've got an advantage over me because you've had some exposure to diesel engines, but like leathermang said, MB does it differently and reading the FSM will help you to understand. Almost everything is covered, and there are numbers and tests and procedures to cover whatever you are doing. FSM, Technical Data book; these two sources of info just about have it all, but keep in mind they are written for MB trained mechanics and translated from German (sometimes poorly), so some thought may be required to puzzle things out.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Amen to that also....and the pictures are often not so good .. so I supplement with the Haynes manual also... but it is really bad about leaving out Warnings which are all over the MB FSM....
Sorta like that ' it takes a village to raise a child' .. it takes a stack of reference materials to figure out what they mean is the correct way...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

You replaced the water pump, was it a stamped steel impeller? Or cast iron?

I had an endless overheating issue in a 240 related to a poor quality replacement water pump. The ones with the cast impeller move a lot more coolant. The difference in surface area on each impeller vane was something like 50% less for the crappy reman

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