In case it may be of help to anyone else doing this for the first time....

1. No need to drain coolant. With hoses clamped, I lost virtually no coolant...no flow at all from heater core.

2. With the duovalve still seated in place, I had a very difficult time removing the hoses. I found that, once I unseated it and removed the electrical connector, I had an easier time removing the hoses.

3. When installing the new one, I made the mistake of attaching the upper hose first. This made it virtually impossible to grip and maneuver the clamp for the lower hose. So I had to reverse the order. Not sure what the advantage is of that style of clamp....seems like clamps that tighten with a ratchet would be easier to work with.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife