In the couple of months I've owned my CDI, operating temp has always risen to a steady 82C. However, I notice that the stock thermostat is 92C. Given that the PO replaced the thermostat at the dealer 35k miles ago, I would assume it's rated at 92C.

Is my 82C a perfectly fine operating temperature? Or should I think about replacing the thermostat?

Of course haven't yet driven the car on a hot summer day...perhaps then it would be closer to 90.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 158k miles
06 E320 CDI "Rutherford", Black on Tan, 177k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 72k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Sherman mine operates about the same parameters as yours but in September with a/c on it reaches 90's. But lately with the cool spell it barely gets into 70's. I need to fine tune my radiator Styrofoam sheet to run a little warmer. It gets a lot better fuel economy when it runs warmer. I had the same issue with my W210 OM606 NA.

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06 MB E320 CDI 123k miles
14 Sienna (wife's DD) 36k miles
11 GL350 Bluetec 136k (Sold)
96 E300; 292k+ miles (Donated)
11 Sprinter 22K+ miles (Sold)

Now that I look at it more carefully, I notice the hash marks are 5C increments. And, if MB compensates for the downward viewing angle, I may be at 90C after all...that gauge isn't very good for precise numbers, especially with my aging eyes.

Wish I could pull actually value like I can with my W210.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 158k miles
06 E320 CDI "Rutherford", Black on Tan, 177k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 72k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife