In the W211, interval is 15 years or 143,000 miles. But that's a long time...so I'd like to test it.

I am unable to find any test strips specifically for Zerex...Valvoline certainly doesn't sell any. But there are some that work with (H)OAT so that's probably my best bet.

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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