Thanks folks. As always, I greatly appreciate the peace of mind that comes with having a vague idea of what's going on. The cap is indeed 1.4 bar, and looks in good order. I did notice a slight menagerie of insect species collected in the radiator ... so I'll entertain the thought of planning a cleaning session. Add that to a list of 2+ hour jobs I need to do if I ever get a block of two hours with reasonable weather, the right tools and an area in which to carry out the procedure ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)