The expansion tank cap on my E300D clearly needs to be replaced....rubber is deteriorated. BUT, I had this experience once before....replaced defective cap, and radiator sprang a leak! Temp seems relatively stable, though I do notice some fluctuation.

Shall I roll the dice?

Maybe 1.2 bar instead of 1.4 bar.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 160k miles
06 E320 CDI "Rutherford", Black on Tan, 180k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 79k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife