i think it is always partially open by your description.if it was not there i think that pump does a short cycle by pass and engine gets hot at freeway speeds.anyway change it and all should be well.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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