Coolant reservoir caps
 

Greetings! I have recently joined this list because I acquired an '85 300TD with only 310,000 miles from the estate of a very good friend who died suddenly in October. I'm very experienced with farm diesel things and also European cars in other respects (and being a language professor by trade, although soon to retire, I can cuss in Swedish, French, German, and Italian), and also, quite a few years ago, helped my friend avoid financial crises by various serious moonlighting work (install short block, head work after a broken timing chain, etc.) on several older (4 cylinder non-turbo) M-B diesels.

Upon examining in detail the car I have acquired, I am beginning to draw up a list of questions for you experts, and it's time to deal with the first: On the radiator of this car, there is a tag which says "Use only radiator cap #120" or something to that effect; the reservoir, however, is capped with one marked "140." What kind of disaster impends (I suspect that this cap has been there for many moons).

It's a 1.4 bar pressure relief as opposed to the original 1.2 bar. The 1.4 is the new recommendation. Just check your hoses for old cracked ones and you're good to go.

I figured that was the case, but
 

I wasn't sure, because other sources said the cap should be 15 psi, which, I believe, is only a hair over 1.0 bar.

Install Evans waterless coolant and you don't need any cap at all

P E H